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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Fri Mar 08, 2019 3:28 pm 

Joined: Wed Feb 20, 2019 3:06 am
Posts: 45
PaulEngr wrote:
Ommi wrote:
I forgot to ask about the above. I was asking what if you or a machine holds the live wire to the chassis in US residential
*continuously* without any upstream overcurrent protective device turning off. How long before it melts the wires or chassis
resulting in a 1.2cal/cm2 energy and molten metal from the melting at arms length away (without any arc flash or Hazard
category 0)?


There isn't a good formula for predicting time to melt. With fuses they basically test it. An uncontrolled experiment with vaporizing or melting wire is not nearly as predictable as a controlled environment like a fuse. And obviously current plays a role in this. Then we get to a question of arcing time. At 120 VAC it's going to self extinguish. I can't put an exact number on it but most likely it will never get there. As far as molten metal goes, try it yourself. It's not very exciting.



Last questions. When you mentioned the word "Self-Extinguish". How many cycles does it happen because
if it self-extinguishes after 30 cycles. Then it's enough to cause an injury. Or did you mean by the
word "Self-Extinguish" something that doesn't even start one cycle or two? So at arms length away it's
0 cal/cm2? Or can it reach say 4.5cal/cm2 before it self extinguishes?

Quote:
Quote:
And to repeat my question in last message:

I nearly ordered the cotton treated PPE today but learnt about "inherently flame resistant" PPE last minute so bought the following
professional suit instead.

Image

Do you know what the Oberon "inherently flame resistant" PPE fabric are made of? See:

https://www.oberoncompany.com/wp-conten ... Series.pdf

https://www.oberoncompany.com/faq/is-ob ... ed-cotton/



You can call and ask on that specific one. Obern makes both the treated cotton and the Nomex grade (considerably more expensive) stuff. The fact that it says "inherently flame resistant" is important because welding greens were first used for arc flash PPE. They lose their retardant properties after about 50 washings. At the same foundry I mentioned we had a mechanic get a severe burn because the greens he was wearing lost their fire retardancy and a piece of slag hit him and lit him up like a candle. The ammonia (Westex ammonia) process that is in use with all arc flash PPE that have been available in several years is chemically bonded to the cotton. There is no way to wash it out unlike welding greens.


I ordered this cheap flame resistant Nomex jacket initially before cancelling it and ordering the professional oberon PPE with inherently flame resistant fabric.

https://www.amazon.com/Magid-Cotton-Arc ... 6CTX3&th=1

"Nomex thread to protect from Arc flash hazards
Flame resistant
9 oz/sq yards 100 percent cotton twill fabric
Inside upper left patch pocket
Concealed front and wrist snap closures "

Is the Nomex thread just on the outside? Can't the cotton underneath still catch fire? the nomex doesn't degrade after 50 washings? It only costs $29 versus the $230 Oberon coverall so I wonder if something is wrong with this Nomex/cotton combo.


Many thanks Paul!


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Sat Mar 09, 2019 8:24 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Ommi wrote:
Last questions. When you mentioned the word "Self-Extinguish". How many cycles does it happen because
if it self-extinguishes after 30 cycles. Then it's enough to cause an injury. Or did you mean by the
word "Self-Extinguish" something that doesn't even start one cycle or two? So at arms length away it's
0 cal/cm2? Or can it reach say 4.5cal/cm2 before it self extinguishes?


One of the problems that the arc flash researchers have had is predicting self-extinguishing. USUALLY it's 1 to 2 cycles maximum. But we can sort of get there through the back door. Some tests have been done with 125 VDC (not VAC) battery systems. They were able to maintain an arc for a maximum of a little under 100 milliseconds (6 cycles) with a 20 kA available fault current. In comparison and this is where we can use your data you've only got 15 kA theoretical maximum with no impedance anywhere except in the transformer. So you can never achieve 20 kA. Also that's DC where you are working with AC. Since AC has zero crossings it won't even make it for that long. I know this is a roundabout answer but there is very, very little published 120 VAC data.

Quote:
Is the Nomex thread just on the outside? Can't the cotton underneath still catch fire? the nomex doesn't degrade after 50 washings? It only costs $29 versus the $230 Oberon coverall so I wonder if something is wrong with this Nomex/cotton combo.


Nomex is a Dupont brand name of an aramid fiber. Kevlar is another one. Whereas Kevlar is optimized for strength (it's actually a para aramid), Nomex is optimized for fire and chemical resistance. Aramids are polymers. The fire retardancy is an inherent property of the material itself. The only way it is going to degrade is if you smear it with something combustible (grease) or get holes in it. Similarly the ammonia process treated cotton is permanently chemically changed. Washing does not affect its fire retardant properties. I believe there are some warnings about bleach but some recent tests how proven that fabric softener does not affect it. It is pretty common to see aramid (Nomex or Kevlar) thread used for the PPE. The way all these are made is that a textile mill makes the special fabric and then a uniform company makes the uniforms. All the test results are on the fabric, NOT the uniform as far as shirts, pants, coveralls, etc., are concerned. But then we run into a problem that the mills don't make treated cotton thread (as far as I know) so the uniform manufacturers usually just use some kind of aramid thread (Kevlar or Nomex) for sewing the seams. The thread itself is very expensive but since so little is used it's not a very expensive item overall.

I'm trying not to discuss very specific brands just in deference to Jim Phillips rules here so here goes.

For $29, you are right to be suspicious but before we look at that, you're talking about two very different markets. Oberon makes multilayer flash suits. They contribute to a lot of the research into arc flash. They are considerably cheaper than Salisbury most of the time but it's still a premium product. Salisbury is sort of the "Fluke" of electrical PPE...you might find better quality but if you assume price = quality, you'll get the best. Oberon makes some of the lightest grade, most comfortable arc flash PPE (and other categories) on the market but it's a small market. The best prices I've gotten for this kind of stuff are from one of the "glove labs" where you send rubber voltage rated gloves, hot sticks, line hose, rubber blankets, etc., to be cleaned and tested. They get huge orders from utilities and they sell a lot of replacement materials too so they get the best discounts on electrical PPE that I've found anywhere for PPE hat is specific to the electrical market. We've been replacing a few 40 cal/cm2 arc flash suits lately. I got the best prices from one of them. They gave me prices for 3 or 4 vendors. The low price brand was only about 5-10% cheaper than Oberon and comfort was less with the cheaper brand so we went with Oberon this time around. Our older equipment is all Salisbury. If you need a multilayer flash suit, that's the direction I'd suggest.

I'd also suggest going for the "kit" route. Why? Price out a hood or a face shield and balaclava alone compared to the whole "kit". The face protection part is about 70% or more of the cost. The "kit" usually saves you a lot of money over assembling components. I have some issues with your approach of thinking you only need to protect the hands/arms. That's not the way it works. Either you need FR PPE and you protect "head to toe" as per 70E or you don't. No going halfway here. Some days when I'm in a substation wearing arc rated shirt and pants doing work on de-energized sections, I definitely feel overdressed. But watch a cutout fuse go off and dump borax everywhere or watch a piece of equipment go up in smoke close by throwing sparks everywhere and you'll quickly become a believer in the idea of FR PPE for "splash damage" even if you are never exposed to anything over 1 cal/cm2. I've been splashed multiple times with slag working in a foundry. It went right through my shirt and jacket but guess what? I didn't turn into a human torch either. It sounds like you might be looking at the 70E tables. That's a reasonable approach without benefit of IEEE 1584 calculations. If that's the case, don't try to do something that isn't in the Code. If you do and you have to answer to OSHA or worse yet, ambulance chasing lawyers, you have 0.0% chance of being able to defend yourself. If you follow 70E, you can use that to fend them off.

Now lets consider the single layer arc rated/FR PPE market. Since it is single layer, we're limited to 12 cal/cm2 or less. Forget about arc rating for a minute and concentrate on the fire retardant (FR) part. Welders need FR PPE. So do coal miners, fire fighters, and iron & steel as well as oil & gas jobs where FR PPE is necessary or at least tradition so it becomes required. We haven't even touched on race car drivers, jet pilots and mechanics, and such. With oil and gas plants in particular it's not uncommon for a contractor to fly into town, hire a crew, buy PPE from a local shop right outside the plant (they might even buy and sell used PPE), then fly back out a week or two later during a shutdown. Price and having the right label is all that matters to them. These groups have been purchasing and using FR PPE much longer than electrical workers. So it's fairly easy for the same PPE manufacturers to "dual rate" FR PPE as arc rated PPE. With a much larger market there is a lot more competition and prices are much better. And let's face it they are far more likely to destroy PPE in the normal course of their work than electrical workers are so they will be buying a lot more all else being equal. It's cheap and plentiful with dozens of brand names. Don't forget too that the rental uniform companies are all mixed up in this same business and often have to unload extra inventory, out of spec, returned (for whatever reason), used or new PPE.

Getting back to the FR vs. AR, all arc rated PPE will be fire retardant. The thing that gives it an ATPV rating is the thermal protection. Basically if you take winter insulated overalls and make them with FR materials, you get an arc rated multilayer overalls. Of course the material has to be tested (ASTM 1959) for label purposes. So as long as we have a thick enough work shirt, pants, coveralls, etc., that is FR rated it becomes arc rated if the company does the testing and adds the information to the label. So in the single layer arc flash PPE market, the same FR vendors easily "upgrade" their products to arc rated. So you can understand then why you can find very inexpensive arc rated single layer PPE on the market.

$29 for coveralls sounds very low though. Even non-FR coveralls are not usually sold that cheap at Walmart. That's about the price of a pair of non-FR budget brand brand work pants. So unless they are clearance or used, something doesn't sound right. I'd suggest maybe looking at glove vendors like I suggested, looking on EBay or Craigs List for used PPE from an oil patch or coal mining vendor or a rental company. Google for instance Rasco which is one of the low cost oil patch brands. BUT also look at Amazon reviews. Some the Rasco products are good quality and some not so much.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Sat Mar 09, 2019 5:48 pm 

Joined: Wed Feb 20, 2019 3:06 am
Posts: 45
PaulEngr wrote:
Ommi wrote:
Last questions. When you mentioned the word "Self-Extinguish". How many cycles does it happen because
if it self-extinguishes after 30 cycles. Then it's enough to cause an injury. Or did you mean by the
word "Self-Extinguish" something that doesn't even start one cycle or two? So at arms length away it's
0 cal/cm2? Or can it reach say 4.5cal/cm2 before it self extinguishes?


One of the problems that the arc flash researchers have had is predicting self-extinguishing. USUALLY it's 1 to 2 cycles maximum. But we can sort of get there through the back door. Some tests have been done with 125 VDC (not VAC) battery systems. They were able to maintain an arc for a maximum of a little under 100 milliseconds (6 cycles) with a 20 kA available fault current. In comparison and this is where we can use your data you've only got 15 kA theoretical maximum with no impedance anywhere except in the transformer. So you can never achieve 20 kA. Also that's DC where you are working with AC. Since AC has zero crossings it won't even make it for that long. I know this is a roundabout answer but there is very, very little published 120 VAC data.



To clarify something. With regards to my open delta 3 phase with 208v high leg (which was the terminal that shorted to the ground producing the primary arc flash)

Do you use the kVA for one transformer in computing for the infinite bus assumption or do you need to add them? For example in the
open delta 3 phase system:

Image

To compute for the infinite bus assumption (ignoring all conductor impedances).. do you just use one transformer kVA (or 75kVA) for 75,000/208/0.02= 18kA
value or do you use other value for the kVA (like 75kVA x 1.5x = 112.5kA)?

I saw the following web site to compute arc flash incident energy in IEEE 1584 2002 edition https://www.jcalc.net/electrical/arc-fl ... lator-ieee
(Let's ignore the latest IEEE 1584 2018 November edition as it was just a few months ago and very complicated)

I entered:

System Voltage: 208 volts
Bolted fault current: 7kA (estimating from the transformer 18kA ssc & conductor impedances)
Conductor gap: 15mm
Grounded
Working distance: 200mm (about 8" or arms length)
Arcing time: 0.016666 sec (2 zero crossings or 1/120 x 2 as it will self extinguish after this time. Say, is your "one cycle" 1/60 or 1/120?)

Result is:

arcing current: 3.549 kA
incident energy at working distance = 0.684 cal/cm2
arc flash boundary = 142.303mm

Is the data above correct? The palm would still be exposed to 1.2cal/cm2 (less than 142mm)?

Is the formula used valid for single phase since IEEE 1584 2002 edition is only for 3 phase system?

Note I don't have any motors in the building except for normal airconditoning for rooms. It's not an industrial plant but only office so I guess there should be simple arc flash formulas for office building only that uses 120/240v open delta 3 phase. BTW.. is it not for 2 phase versus 3 phase, the incident energy is the same if only two conductors are involved in the arc flash (and not three)? In my office building. The initial arc flash is between the 208v high leg and ground, then it progress a bit to phase to phase arc flash but only very minimal as only the screw heads were melted between middle 120v terminal and last 208 high leg terminal. The first terminal isn't involved in the arc flash. So can you treat 2 conductor arc flash in 3 phase as a single phase event?


Quote:
Quote:
Is the Nomex thread just on the outside? Can't the cotton underneath still catch fire? the nomex doesn't degrade after 50 washings? It only costs $29 versus the $230 Oberon coverall so I wonder if something is wrong with this Nomex/cotton combo.


Nomex is a Dupont brand name of an aramid fiber. Kevlar is another one. Whereas Kevlar is optimized for strength (it's actually a para aramid), Nomex is optimized for fire and chemical resistance. Aramids are polymers. The fire retardancy is an inherent property of the material itself. The only way it is going to degrade is if you smear it with something combustible (grease) or get holes in it. Similarly the ammonia process treated cotton is permanently chemically changed. Washing does not affect its fire retardant properties. I believe there are some warnings about bleach but some recent tests how proven that fabric softener does not affect it. It is pretty common to see aramid (Nomex or Kevlar) thread used for the PPE. The way all these are made is that a textile mill makes the special fabric and then a uniform company makes the uniforms. All the test results are on the fabric, NOT the uniform as far as shirts, pants, coveralls, etc., are concerned. But then we run into a problem that the mills don't make treated cotton thread (as far as I know) so the uniform manufacturers usually just use some kind of aramid thread (Kevlar or Nomex) for sewing the seams. The thread itself is very expensive but since so little is used it's not a very expensive item overall.

I'm trying not to discuss very specific brands just in deference to Jim Phillips rules here so here goes.

For $29, you are right to be suspicious but before we look at that, you're talking about two very different markets. Oberon makes multilayer flash suits. They contribute to a lot of the research into arc flash. They are considerably cheaper than Salisbury most of the time but it's still a premium product. Salisbury is sort of the "Fluke" of electrical PPE...you might find better quality but if you assume price = quality, you'll get the best. Oberon makes some of the lightest grade, most comfortable arc flash PPE (and other categories) on the market but it's a small market. The best prices I've gotten for this kind of stuff are from one of the "glove labs" where you send rubber voltage rated gloves, hot sticks, line hose, rubber blankets, etc., to be cleaned and tested. They get huge orders from utilities and they sell a lot of replacement materials too so they get the best discounts on electrical PPE that I've found anywhere for PPE hat is specific to the electrical market. We've been replacing a few 40 cal/cm2 arc flash suits lately. I got the best prices from one of them. They gave me prices for 3 or 4 vendors. The low price brand was only about 5-10% cheaper than Oberon and comfort was less with the cheaper brand so we went with Oberon this time around. Our older equipment is all Salisbury. If you need a multilayer flash suit, that's the direction I'd suggest.

I'd also suggest going for the "kit" route. Why? Price out a hood or a face shield and balaclava alone compared to the whole "kit". The face protection part is about 70% or more of the cost. The "kit" usually saves you a lot of money over assembling components. I have some issues with your approach of thinking you only need to protect the hands/arms. That's not the way it works. Either you need FR PPE and you protect "head to toe" as per 70E or you don't. No going halfway here. Some days when I'm in a substation wearing arc rated shirt and pants doing work on de-energized sections, I definitely feel overdressed. But watch a cutout fuse go off and dump borax everywhere or watch a piece of equipment go up in smoke close by throwing sparks everywhere and you'll quickly become a believer in the idea of FR PPE for "splash damage" even if you are never exposed to anything over 1 cal/cm2. I've been splashed multiple times with slag working in a foundry. It went right through my shirt and jacket but guess what? I didn't turn into a human torch either. It sounds like you might be looking at the 70E tables. That's a reasonable approach without benefit of IEEE 1584 calculations. If that's the case, don't try to do something that isn't in the Code. If you do and you have to answer to OSHA or worse yet, ambulance chasing lawyers, you have 0.0% chance of being able to defend yourself. If you follow 70E, you can use that to fend them off.

Now lets consider the single layer arc rated/FR PPE market. Since it is single layer, we're limited to 12 cal/cm2 or less. Forget about arc rating for a minute and concentrate on the fire retardant (FR) part. Welders need FR PPE. So do coal miners, fire fighters, and iron & steel as well as oil & gas jobs where FR PPE is necessary or at least tradition so it becomes required. We haven't even touched on race car drivers, jet pilots and mechanics, and such. With oil and gas plants in particular it's not uncommon for a contractor to fly into town, hire a crew, buy PPE from a local shop right outside the plant (they might even buy and sell used PPE), then fly back out a week or two later during a shutdown. Price and having the right label is all that matters to them. These groups have been purchasing and using FR PPE much longer than electrical workers. So it's fairly easy for the same PPE manufacturers to "dual rate" FR PPE as arc rated PPE. With a much larger market there is a lot more competition and prices are much better. And let's face it they are far more likely to destroy PPE in the normal course of their work than electrical workers are so they will be buying a lot more all else being equal. It's cheap and plentiful with dozens of brand names. Don't forget too that the rental uniform companies are all mixed up in this same business and often have to unload extra inventory, out of spec, returned (for whatever reason), used or new PPE.

Getting back to the FR vs. AR, all arc rated PPE will be fire retardant. The thing that gives it an ATPV rating is the thermal protection. Basically if you take winter insulated overalls and make them with FR materials, you get an arc rated multilayer overalls. Of course the material has to be tested (ASTM 1959) for label purposes. So as long as we have a thick enough work shirt, pants, coveralls, etc., that is FR rated it becomes arc rated if the company does the testing and adds the information to the label. So in the single layer arc flash PPE market, the same FR vendors easily "upgrade" their products to arc rated. So you can understand then why you can find very inexpensive arc rated single layer PPE on the market.

$29 for coveralls sounds very low though. Even non-FR coveralls are not usually sold that cheap at Walmart. That's about the price of a pair of non-FR budget brand brand work pants. So unless they are clearance or used, something doesn't sound right. I'd suggest maybe looking at glove vendors like I suggested, looking on EBay or Craigs List for used PPE from an oil patch or coal mining vendor or a rental company. Google for instance Rasco which is one of the low cost oil patch brands. BUT also look at Amazon reviews. Some the Rasco products are good quality and some not so much.


Many thanks for the above info.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Sat Mar 09, 2019 7:31 pm 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Ommi wrote:
To clarify something. With regards to my open delta 3 phase with 208v high leg (which was the terminal that shorted to the ground producing the primary arc flash)

Do you use the kVA for one transformer in computing for the infinite bus assumption or do you need to add them? For example in the
open delta 3 phase system:

Image

To compute for the infinite bus assumption (ignoring all conductor impedances).. do you just use one transformer kVA (or 75kVA) for 75,000/208/0.02= 18kA
value or do you use other value for the kVA (like 75kVA x 1.5x = 112.5kA)?

I saw the following web site to compute arc flash incident energy in IEEE 1584 2002 edition https://www.jcalc.net/electrical/arc-fl ... lator-ieee
(Let's ignore the latest IEEE 1584 2018 November edition as it was just a few months ago and very complicated)


I'm never good at these screwy transformer calculations but here goes. Phase-to-phase will be 240 VAC. The high leg is 208 V to ground as it shows up on the sticker but the voltage from the high leg to another phase leg is 240 VAC. The whole point of a high leg delta system (other than saving 1/3 of the cost in a two transformer broken delta) is that you get a 3 phase output (240 VAC delta) and 240/120 VAC single phase output simultaneously. On a balanced 3 phase system we don't really care where the grounded voltage reference is there as long as it's there to keep problems with transients (system capacitance) under control. The impedance is fairly high and you get lots of unbalanced loading on the transformer but this isn't a high performance solution where we'd use a traditional delta-wye.

According to test results on arc flash where they have tested single vs. three phase, there is little difference between the results. This kind of makes sense when you realize that at any given time with all three phases being about 120 degrees apart in a three phase system on average one of the phases will be close to zero while the other two have voltage on them so a three phase arc is more like a rotating single phase arc. IEEE 1584-2002 and 2018 recommend just treating it as 3 phase.

Quote:
I entered:

System Voltage: 208 volts
Bolted fault current: 7kA (estimating from the transformer 18kA ssc & conductor impedances)
Conductor gap: 15mm
Grounded
Working distance: 200mm (about 8" or arms length)
Arcing time: 0.016666 sec (2 zero crossings or 1/120 x 2 as it will self extinguish after this time. Say, is your "one cycle" 1/60 or 1/120?)


You put in one cycle (1/60th second). But I'd use the conservative best result I have which is 100 ms. PG&E only showed about 2 cycles in their tests (0.033 s) but subsequent box-barrier tests where we have vertical electrodes entering into something substantial such as a circuit breaker lasted much longer. So I'd use the worst case DC result of about 0.1 seconds if we're doing it this way. Obviously we're guessing anyways since we have no way to predict self-extinguishment.

Quote:
Result is:

arcing current: 3.549 kA
incident energy at working distance = 0.684 cal/cm2
arc flash boundary = 142.303mm


The problem is your working distance. So the arm is 8" away. But the hand is more like 3-4" away so it is roughly 2-3 cal/cm2. And the fingers will be even closer. If we have an exponent of 2 (open air) which it will be given the short distances away where the box isn't going to have much influence, it goes up by a factor of 4 every time we cut the distance in half and goes exponential at the fingers. OSHA (1910.269) states ot use 15" minimum (glove work). 70E uses 18".

Quote:
Is the data above correct? The palm would still be exposed to 1.2cal/cm2 (less than 142mm)?


Hard to say. All the data for 1584 is taken at a couple feet away so we don't have data on something this close in. We have no practical way to estimate opening time. The arcing current is way too high but we don't have a more complete model to work from so we need to be conservative on the opening time of whatever overcurrent device the utility has.

Quote:
Is the formula used valid for single phase since IEEE 1584 2002 edition is only for 3 phase system?


As per 1584, no it's not. The ArcPro and HeatFlux models are single phase but they are designed for much higher voltages. 1584 recommends just treating it as 3 phase knowing that the result will be lower but there isn't test data to say how much lower.

Quote:
Note I don't have any motors in the building except for normal airconditoning for rooms. It's not an industrial plant but only office so I guess there should be simple arc flash formulas for office building only that uses 120/240v open delta 3 phase. BTW.. is it not for 2 phase versus 3 phase, the incident energy is the same if only two conductors are involved in the arc flash (and not three)? In my office building. The initial arc flash is between the 208v high leg and ground, then it progress a bit to phase to phase arc flash but only very minimal as only the screw heads were melted between middle 120v terminal and last 208 high leg terminal. The first terminal isn't involved in the arc flash. So can you treat 2 conductor arc flash in 3 phase as a single phase event?


You can. You know that the real result will be less but we're looking to quantify a hazard here. An upper bound will do.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Sat Mar 09, 2019 8:53 pm 

Joined: Wed Feb 20, 2019 3:06 am
Posts: 45
PaulEngr wrote:
Ommi wrote:
To clarify something. With regards to my open delta 3 phase with 208v high leg (which was the terminal that shorted to the ground producing the primary arc flash)

Do you use the kVA for one transformer in computing for the infinite bus assumption or do you need to add them? For example in the
open delta 3 phase system:

Image

To compute for the infinite bus assumption (ignoring all conductor impedances).. do you just use one transformer kVA (or 75kVA) for 75,000/208/0.02= 18kA
value or do you use other value for the kVA (like 75kVA x 1.5x = 112.5kA)?

I saw the following web site to compute arc flash incident energy in IEEE 1584 2002 edition https://www.jcalc.net/electrical/arc-fl ... lator-ieee
(Let's ignore the latest IEEE 1584 2018 November edition as it was just a few months ago and very complicated)


I'm never good at these screwy transformer calculations but here goes. Phase-to-phase will be 240 VAC. The high leg is 208 V to ground as it shows up on the sticker but the voltage from the high leg to another phase leg is 240 VAC. The whole point of a high leg delta system (other than saving 1/3 of the cost in a two transformer broken delta) is that you get a 3 phase output (240 VAC delta) and 240/120 VAC single phase output simultaneously. On a balanced 3 phase system we don't really care where the grounded voltage reference is there as long as it's there to keep problems with transients (system capacitance) under control. The impedance is fairly high and you get lots of unbalanced loading on the transformer but this isn't a high performance solution where we'd use a traditional delta-wye.


I know phase to phase is 240v even if phase to neutral of the high leg is 208v because I actually measured them with a voltmeter many years ago. What I was asking was since the arc flash formed between the 208v high leg to the chassis neutral where it blew a big hole at the chassis (same intensity of damage as the lugs shown in earlier picture):

Image

before painting on chassis
Image

Then I was asking since the arc flash formed between the 208v to neutral (or ground of the chassis). And since in the illustration the 208v is between the phase of one transformer to the centertapped neutral of another (so 1.5x windings are used), whether you just use the 75kVA of one transformer only in computing for the infinite bus assumption or whether you multiply the 75kVA by 1.5x to get 112,500A to come up with 112,500/208/0.02= 27kVA short circuit current at the transformers terminals (ignoring the conductor impedances).

Quote:
According to test results on arc flash where they have tested single vs. three phase, there is little difference between the results. This kind of makes sense when you realize that at any given time with all three phases being about 120 degrees apart in a three phase system on average one of the phases will be close to zero while the other two have voltage on them so a three phase arc is more like a rotating single phase arc. IEEE 1584-2002 and 2018 recommend just treating it as 3 phase.

Quote:
I entered:

System Voltage: 208 volts
Bolted fault current: 7kA (estimating from the transformer 18kA ssc & conductor impedances)
Conductor gap: 15mm
Grounded
Working distance: 200mm (about 8" or arms length)
Arcing time: 0.016666 sec (2 zero crossings or 1/120 x 2 as it will self extinguish after this time. Say, is your "one cycle" 1/60 or 1/120?)


You put in one cycle (1/60th second). But I'd use the conservative best result I have which is 100 ms. PG&E only showed about 2 cycles in their tests (0.033 s) but subsequent box-barrier tests where we have vertical electrodes entering into something substantial such as a circuit breaker lasted much longer. So I'd use the worst case DC result of about 0.1 seconds if we're doing it this way. Obviously we're guessing anyways since we have no way to predict self-extinguishment.

Quote:
Result is:

arcing current: 3.549 kA
incident energy at working distance = 0.684 cal/cm2
arc flash boundary = 142.303mm


The problem is your working distance. So the arm is 8" away. But the hand is more like 3-4" away so it is roughly 2-3 cal/cm2. And the fingers will be even closer. If we have an exponent of 2 (open air) which it will be given the short distances away where the box isn't going to have much influence, it goes up by a factor of 4 every time we cut the distance in half and goes exponential at the fingers. OSHA (1910.269) states ot use 15" minimum (glove work). 70E uses 18".


Since most electrical staff put their hands close to the conductors like turning off breakers then during arc flashes. Don't there fingers got burned? And if arc flashed survivors no longer have fingers, how can they work again? In the above picture, note the breaker handles are very close to the terminals. So how can we turn if on or off without the hands close to it (or when inserting the live wire to the terminals in case POCO won't turn off the power due to many paperworks). Do you know of a stick plastic lever to turn the handle off or on?

Quote:
Quote:
Is the data above correct? The palm would still be exposed to 1.2cal/cm2 (less than 142mm)?


Hard to say. All the data for 1584 is taken at a couple feet away so we don't have data on something this close in. We have no practical way to estimate opening time. The arcing current is way too high but we don't have a more complete model to work from so we need to be conservative on the opening time of whatever overcurrent device the utility has.

Quote:
Is the formula used valid for single phase since IEEE 1584 2002 edition is only for 3 phase system?


As per 1584, no it's not. The ArcPro and HeatFlux models are single phase but they are designed for much higher voltages. 1584 recommends just treating it as 3 phase knowing that the result will be lower but there isn't test data to say how much lower.

Quote:
Note I don't have any motors in the building except for normal airconditoning for rooms. It's not an industrial plant but only office so I guess there should be simple arc flash formulas for office building only that uses 120/240v open delta 3 phase. BTW.. is it not for 2 phase versus 3 phase, the incident energy is the same if only two conductors are involved in the arc flash (and not three)? In my office building. The initial arc flash is between the 208v high leg and ground, then it progress a bit to phase to phase arc flash but only very minimal as only the screw heads were melted between middle 120v terminal and last 208 high leg terminal. The first terminal isn't involved in the arc flash. So can you treat 2 conductor arc flash in 3 phase as a single phase event?


You can. You know that the real result will be less but we're looking to quantify a hazard here. An upper bound will do.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Sun Mar 10, 2019 6:59 am 
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The current determines the arc energy flux (power) for the most part. The time determines the energy released. And there is one more critical factor: arc gap. Arc flash testing at 480 V usually uses arc gaps in the 1/2" to 1" range. At 208 V it is hard to get an arc to be self sustaining with an arc gap over 1/4". At 120 VAC we're starting to look at a couple millimeters at most (arc welding distances). With such a small arc length, flux (arc power) is constrained by the short arc gap. So I'm not sure what assumptions you used in your calculation but you need to be setting a reasonable arc gap, too, and 25 mm is not it.

Going a little further, the wiring used for low voltage distribution and controls is usually mostly #12 or #14. It occasionally gets to #10 for voltage drop reasons. Despite the ampacities, NEC rules actually set much more breaker sizes for smaller wiring in residential and commercial use. For instance #14 at 75 C has an ampacity of 20 A but the breaker size is specified as 15 A. Except for appliance circuits, laundry, and recently a garage circuit, residential breakers and receptacles are all 15 A. Magnetic trips are usually set at most to 10 times the thermal trip setting or 150 A. And you were just calculating short circuits into the thousands of amps. So clearly we are going to trip "instantaneously" for the vast majority of commercial/residential loads. With miniature breakers they usually trip in under 1 cycle (0.016 s). Both dual element and fast blow fuses are going to trip in 1/4 cycle (0.004 seconds) under these conditions.

In addition at 480 V most of the arc flash testing is done with 1/2" to 1" arc gaps, venturing into longer arc gaps only with extremely high fault currents because arc flash testing is done with stable arcs (arc instability is hard to predict). But the original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result. All the other 208 V results failed because they never got to a stable arc. The original testing used 1/2" arc gaps. The new test data set used to develop IEEE 1584-2018 includes 1/4" gaps and used much thinner "fuse" wires to get stable arcing to occur down to 208 VAC. The obvious consequence here is that it is nearly impossible to have a stable arc at 1/2" (12 mm). Stable 208 V arcs are very short, closer to 10-15 mm at most. But going back to our arc flash energy this also means greatly reduced arcing energy. Try it with the web site you used. You'll see a dramatic reduction with a 4 mm arc gap, never mind a 2 mm arc gap.

So I'm telling you that most of the time and almost all circumstances when working with low voltage (<300 V) systems, arc flash is simply not a serious issue. In fact it is so minor of an issue that the IEEE 1584-2002 standard actually stated that for UNDER 240 VAC (probably should have been AT) fed by a single transformer rated 125 kVA or less, arc flash "need not be considered". In fact that describes your scenario. And some testing done at PG&E (a utility) published back then even showed that arcs would extinguish at those voltages in 1 to 2 cycles. They only got a single test case at 208 VAC with the highest available fault current to work in the tests that were used to develop the original IEEE 1584-2002 equations. In fact with around 15 years of active research on arc flash, it took until 2009 before there was even a recorded fatality. Think about that...15-20 years straight with more electricians working on 240/120 and 208/120 systems without a single arc flash fatality. With all the engineering above you can probably see why this is an almost impossible situation.

Now let's consider human behavior a little bit at this point. Have you ever observed residential and controls technicians working on distribution panels? They scare those of us that work industrial and large commercial operations. They just open everything up and start moving energized wires around, leaving them hanging out exposed, never shut off a breaker, you name it. How about disconnecting a load? Just yank the plug out of the receptacle, energized or not. On a breaker, same thing. Just lift the hot. LOTO? What are you talking about? Have you actually seen what passes for a "lockout device" on a distribution panel? It's a joke. But there's a reason for it. The slowest breaker in the panel is going to be the main distribution panel breaker and that one is still going to be in the 1-2 cycle trip speed range. It has to trip slower than the 15 and 20 A breakers that it is feeding but that's it. It might still trip as fast as the smaller breakers but something called dynamic resistance comes into play which allows breakers to trip almost at the same speed and still coordinate properly. Want to know what happens if an "arc flash" happens in this environment? Ask around. You'll get the guy that tells you about the time that he accidentally touched a hot wire to the neutral or ground bar energized when he wasn't supposed to. So he used the standard electrician's first aid kit...wrapping his fingers in electrical tape so that the foreman wouldn't see the blisters. Is this going to be the extent of the injury? I think you should know by now that I can't guarantee it but trust me. My grandfather was an electrician for the telephone company, back when there was only one. My dad and grandfather did all kinds of electrical work on the farm where I grew up. I know what goes on because I've done it myself. I know exactly how many guys have gotten injured or killed doing this. Because when we started getting serious about arc flash it was thought that there was no risk at the voltages you are dealing with. In fact it took decades for someone to get killed doing it. I know because I've gone through hundreds of OSHA reports doing some research on subjects like this for a former employer. We had the same kinds of questions about low voltage. That's when I uncovered the 2009 OSHA case. And that's where we're going to next.

Lets step up to the utility side of things. The utility fuse or breaker must trip slower than the main in the distribution panel. AND the utility fuse or breaker is not seeing the 15 kA worth of fault current you calculated on the secondary side. It's seeing the fault current on the primary side. So even with a very low 480 V distribution voltage, it is seeing less than half the fault current. At higher voltages (say 4160 V), the fault current is less than 10% of what you calculated. On top of that, the inrush on your 2% impedance transformer is extremely high. So the cutout fuse out of necessity must be designed to either operate slowly or sized to be so large that it only reacts to short circuits. So it offers you almost no protection whatsoever on the secondary side except for removing dead shorted services from the system. Linemen know this. That's why they operate the cutout with a hot stick and work at glove distance on everything even if it's "only" 208/120. So going back to our assumptions, IF we can get a stable arc, we can certainly get a significant arc flash. They finally demonstrated that it can happen in laboratory conditions in the last 10 years, and an electrician in Georgia "proved" it can happen in 2009. Two electricians were assigned to remove a temporary construction panel. They were dressed in standard work attire for summer work in Georgia for residential electricians, flip flops, shorts, and tank tops (this was actually mentioned in the OSHA report). They decided that they didn't want to wait for the lineman to arrive so they began disassembling the live distribution panel. Something happened (not documented in OSHA's summary) that caused an arc flash. I don't know what happened for sure but I can guess that it is probably something very much like the incident that happened twice at your facility. Both electricians went to the hospital and one of them died from injuries a couple days later. Can I be any more clear about the consequences than this?

Quote:
Since most electrical staff put their hands close to the conductors like turning off breakers then during arc flashes. Don't there fingers got burned? And if arc flashed survivors no longer have fingers, how can they work again? In the above picture, note the breaker handles are very close to the terminals. So how can we turn if on or off without the hands close to it (or when inserting the live wire to the terminals in case POCO won't turn off the power due to many paperworks). Do you know of a stick plastic lever to turn the handle off or on?


If you really want to go there, CBS (Circuit Breaker Sales) sells a "chicken switch"...remote operator. But before you do, please review the informational note in 70E:

130.(7)(a) Informational Note #2: “It is the collective experience of the Technical Committee on Electrical Safety in the Workplace that normal operation of enclosed electrical equipment, operating at 600 volts or less, that has been properly installed and maintained by qualified persons is not likely to expose the employee to an electrical hazard.”

They are not saying that it CAN'T happen but that it is highly unlikely that it will. In fact there is an OSHA case of an improper repair at a parking garage where the parking garage attendant flipped the breakers (hopefully SWD rated) at the end of the night and the panel exploded. An electrician had previously just jammed a piece of sheet metal between the breakers and the inner cover to blank off an unused slot. The piece of sheet metal fell out and hit the bus in the distribution panel. The attendant was burned, not killed. But this sort of activity happens thousands of times every day without any injury whatsoever. Which is why for almost the one and only time the 70E Technical Committee actually stuck their necks out.

What I'm trying to get across here and that's also what 70E is stating is that under normal circumstances electrical equipment is safe to operate. The CPSC would never allow electrical equipment in residential applications if it wasn't safe to operate. The exact same equipment is used in commercial systems all the time. Industrial and utility equipment is really not that much different except the sizes and designs change, and we shift from unqualified to qualified workers. Put simply what the 70E Committee is saying in another way is that at least low voltage electrical equipment is not inherently dangerous.

What makes this stuff dangerous is not the equipment itself, nor normal operation of it. It becomes dangerous under two circumstances. As stated either it isn't properly installed or maintained. As it degrades it becomes dangerous to operate. So the first thing you have to do before putting it back into service (NEMA AB-4 speaking here) is to do the inspections and maintenance necessary to put it back safely into service. On miniature and molded case breakers, that's about a 1 minute task. If it's defective you replace it which takes minutes, not hours. And I don't think anyone would have any intention or desire to ever put a molded case breaker back into service that is defective if they know what can happen.

The second circumstance is doing stupid things. Working live when you don't have to. Working live especially when it is obvious that the equipment is already damaged so you should expect the unexpected...when the statement from the 70E Technical Committee no longer applies. Working live without proper protection and training in doing so, particularly when the equipment was never designed and intended for energized work in the first place. And doing a half assed repair. Linemen land cables onto energized lines all the time. They use a "hot line clamp" (google this) to do it. They do it with a hot stick and/or rubber gloves and they do it safely all the time. They do it almost every time they go to de-energize a line too because their work rules require them to install temporary grounding on the line to short all the phases to ground before they perform de-energized work. Often when you remove it, it will draw a pretty impressive looking (but harmless) arc caused by residual voltages that we cannot easily remove. They wear arc flash PPE as well as rubber gloves and leather protectors for doing energized work, sometimes including sleeves that go up to your arm pits. I know because I am trained to do this and I have the same equipment on my truck right now. I do medium voltage (1000 - 35,400 V) work. I have sticks, gloves, sleeves, and ground cluster. I maintain it and I'm trained to use all of it. This is very different from say attempting to land a live service connection on top of an open molded case breaker. You ride the bull bare back, expect to get the horn! Ride 'em cowboy!

Finally when it comes to repairs, this is the actual requirement for ALL electrical repairs whether field or shop: you restore the equipment back to it's original condition.

A rule of thumb for dielectric testing is twice the maximum voltage plus 1,000 V. So for your breaker if it is actually 300 V class (doubtful) we'd apply a 1600 VAC test voltage to it and look for no more than a 1 mA leakage. Or 1.6 megaohms as insulation resistance. If it is 600 V class (most of them are) then this goes up to 2400 VAC and we're looking for 2.4 megaohms or again 1 mA leakage maximum. Motor specs are actually quite a bit higher than this. With molded case breakers the breaker has to be at least 2500 A or larger before repairing it will be less expensive than replacement. But for the equipment that we repair in our shop first we would use dry ice abrasive blasting to remove any and all soot and smoke damage. Depending on circumstances we use denatured alcohol and breaker cleaner to scrub it off in the field or dry ice blasting for larger areas. We'd also replace anything that is structurally damaged. Possibly including welding, grinding, machining, etc., if we can't replace it. Coils get vacuum impregnated with varnish or epoxy (we mostly epoxy these days) then baked to cure. Finally we'd paint metal surfaces with an insulating paint and then test everything to verify it meets standards before sending it back out or energizing it. The acids in smoke often degrade critical items like breakers from the acids in the smoke. The damage often doesn't show up until days or weeks later so when it doubt, replace.

As to what is "enough" insulation or enough clearance...the specifications are testing or performance specifications. There is computer software (again costing thousands) that can estimate clearances but it is really best for testing out ideas, not final results. It reduces the cost of experimental testing for manufacturers but you can't expect it to generate precision results (too many unknowns and variables). So manufacturers build mockups and test them. Then finally they submit samples to the third party testing labs for final certification. You can't possibly do that in the field. So field work relies on one of two approaches. Either we restore back to factory original conditions, or else we use practical rules of thumb that are extremes. For instance a common rule of thumb for 600 V systems is to maintain a separation of at least 3/4" in air, or a minimum of 3/8" with fully insulated barriers. I think you will notice that this is exactly the spacing that the manufacturers also use for the lug spacing on most breakers.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Sun Mar 10, 2019 4:13 pm 

Joined: Wed Feb 20, 2019 3:06 am
Posts: 45
PaulEngr wrote:
The current determines the arc energy flux (power) for the most part. The time determines the energy released. And there is one more critical factor: arc gap. Arc flash testing at 480 V usually uses arc gaps in the 1/2" to 1" range. At 208 V it is hard to get an arc to be self sustaining with an arc gap over 1/4". At 120 VAC we're starting to look at a couple millimeters at most (arc welding distances). With such a small arc length, flux (arc power) is constrained by the short arc gap. So I'm not sure what assumptions you used in your calculation but you need to be setting a reasonable arc gap, too, and 25 mm is not it.

Going a little further, the wiring used for low voltage distribution and controls is usually mostly #12 or #14. It occasionally gets to #10 for voltage drop reasons. Despite the ampacities, NEC rules actually set much more breaker sizes for smaller wiring in residential and commercial use. For instance #14 at 75 C has an ampacity of 20 A but the breaker size is specified as 15 A. Except for appliance circuits, laundry, and recently a garage circuit, residential breakers and receptacles are all 15 A. Magnetic trips are usually set at most to 10 times the thermal trip setting or 150 A. And you were just calculating short circuits into the thousands of amps. So clearly we are going to trip "instantaneously" for the vast majority of commercial/residential loads. With miniature breakers they usually trip in under 1 cycle (0.016 s). Both dual element and fast blow fuses are going to trip in 1/4 cycle (0.004 seconds) under these conditions.

In addition at 480 V most of the arc flash testing is done with 1/2" to 1" arc gaps, venturing into longer arc gaps only with extremely high fault currents because arc flash testing is done with stable arcs (arc instability is hard to predict). But the original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result. All the other 208 V results failed because they never got to a stable arc. The original testing used 1/2" arc gaps. The new test data set used to develop IEEE 1584-2018 includes 1/4" gaps and used much thinner "fuse" wires to get stable arcing to occur down to 208 VAC. The obvious consequence here is that it is nearly impossible to have a stable arc at 1/2" (12 mm). Stable 208 V arcs are very short, closer to 10-15 mm at most. But going back to our arc flash energy this also means greatly reduced arcing energy. Try it with the web site you used. You'll see a dramatic reduction with a 4 mm arc gap, never mind a 2 mm arc gap.

So I'm telling you that most of the time and almost all circumstances when working with low voltage (<300 V) systems, arc flash is simply not a serious issue. In fact it is so minor of an issue that the IEEE 1584-2002 standard actually stated that for UNDER 240 VAC (probably should have been AT) fed by a single transformer rated 125 kVA or less, arc flash "need not be considered". In fact that describes your scenario. And some testing done at PG&E (a utility) published back then even showed that arcs would extinguish at those voltages in 1 to 2 cycles. They only got a single test case at 208 VAC with the highest available fault current to work in the tests that were used to develop the original IEEE 1584-2002 equations. In fact with around 15 years of active research on arc flash, it took until 2009 before there was even a recorded fatality. Think about that...15-20 years straight with more electricians working on 240/120 and 208/120 systems without a single arc flash fatality. With all the engineering above you can probably see why this is an almost impossible situation.

Now let's consider human behavior a little bit at this point. Have you ever observed residential and controls technicians working on distribution panels? They scare those of us that work industrial and large commercial operations. They just open everything up and start moving energized wires around, leaving them hanging out exposed, never shut off a breaker, you name it. How about disconnecting a load? Just yank the plug out of the receptacle, energized or not. On a breaker, same thing. Just lift the hot. LOTO? What are you talking about? Have you actually seen what passes for a "lockout device" on a distribution panel? It's a joke. But there's a reason for it. The slowest breaker in the panel is going to be the main distribution panel breaker and that one is still going to be in the 1-2 cycle trip speed range. It has to trip slower than the 15 and 20 A breakers that it is feeding but that's it. It might still trip as fast as the smaller breakers but something called dynamic resistance comes into play which allows breakers to trip almost at the same speed and still coordinate properly. Want to know what happens if an "arc flash" happens in this environment? Ask around. You'll get the guy that tells you about the time that he accidentally touched a hot wire to the neutral or ground bar energized when he wasn't supposed to. So he used the standard electrician's first aid kit...wrapping his fingers in electrical tape so that the foreman wouldn't see the blisters. Is this going to be the extent of the injury? I think you should know by now that I can't guarantee it but trust me. My grandfather was an electrician for the telephone company, back when there was only one. My dad and grandfather did all kinds of electrical work on the farm where I grew up. I know what goes on because I've done it myself. I know exactly how many guys have gotten injured or killed doing this. Because when we started getting serious about arc flash it was thought that there was no risk at the voltages you are dealing with. In fact it took decades for someone to get killed doing it. I know because I've gone through hundreds of OSHA reports doing some research on subjects like this for a former employer. We had the same kinds of questions about low voltage. That's when I uncovered the 2009 OSHA case. And that's where we're going to next.

Lets step up to the utility side of things. The utility fuse or breaker must trip slower than the main in the distribution panel. AND the utility fuse or breaker is not seeing the 15 kA worth of fault current you calculated on the secondary side. It's seeing the fault current on the primary side. So even with a very low 480 V distribution voltage, it is seeing less than half the fault current. At higher voltages (say 4160 V), the fault current is less than 10% of what you calculated. On top of that, the inrush on your 2% impedance transformer is extremely high. So the cutout fuse out of necessity must be designed to either operate slowly or sized to be so large that it only reacts to short circuits. So it offers you almost no protection whatsoever on the secondary side except for removing dead shorted services from the system. Linemen know this. That's why they operate the cutout with a hot stick and work at glove distance on everything even if it's "only" 208/120. So going back to our assumptions, IF we can get a stable arc, we can certainly get a significant arc flash. They finally demonstrated that it can happen in laboratory conditions in the last 10 years, and an electrician in Georgia "proved" it can happen in 2009. Two electricians were assigned to remove a temporary construction panel. They were dressed in standard work attire for summer work in Georgia for residential electricians, flip flops, shorts, and tank tops (this was actually mentioned in the OSHA report). They decided that they didn't want to wait for the lineman to arrive so they began disassembling the live distribution panel. Something happened (not documented in OSHA's summary) that caused an arc flash. I don't know what happened for sure but I can guess that it is probably something very much like the incident that happened twice at your facility. Both electricians went to the hospital and one of them died from injuries a couple days later. Can I be any more clear about the consequences than this?


First of all. When you mentioned earlier that for arc flash that can self-extinguish and it can do that in 1 to 2 cycles. I'm assuming that within the 1 to 2 cycles before it self-extinguishes, it can already vaporize metals and cause injury to the fingers or hands fo the electrician. You seem to be saying above that for arc flash that self extinguishes in 1 to 2 cycle. It can't produce any damage? This is important as I was assuming it could cause damage already. So you are basically saying only arc flash that is stable can do damage?

Second. You mentioned in first part of the paragraphs above that arc flash can't sustain below 300v and safe so arc flash needn't be considered, yet the last part you mentioned about the electrician killed in Georgia by arc flash working in 120/240v. It's confusing. I've actually thought of the above the entire day. You are saying only stable arc flash can injure or cause damage. And it can't occur below 300v. So what conditions was able to create stable arc enough to killed the electrician in Georgia?

Third, I was asking you earlier video of how short circuit without arc flash look like. And you said it just jerked around. But you mentioned about electricians getting injured or killed in your younger days even working with panels that don't have arc flashes. Besides electrocution, how else can the electrician get injured if there is short circuit when arc flash didn't occur?

Combining all the above:

1. Based on the pictures of the arc flashed breakers in my panel. Do you think it was just short circuit without arc flash or short circuit with arc flash?

2. If there was arc flash, was it stable arc flash or not? I was assuming before I read this message that arc flashed that self-extinguishes in 1 to 2 cycle can already vaporize metals and cause 2nd degree burn.

3. If it was not arc flash. Then for working under 300v, how do you simulate or repeat the damage in my breakers. Are you saying any dead short or short circuit without arc flash can vaporize metals and injure people? But earlier you said the wire just jerked around in short circuit.

4. If it (my melted breaker lugs and hole in chassis) was caused by arc flash. That means it was stable arc flash that can vaporize and injure people. Why did it happen when it was not supposed to happen below 300V. Maybe it was just very rare bad luck where at the instant the electrician lowered the live wire, there was a transient that increased the voltage and current enough to cause stable arc flash that shouldn't have occurred.

5. If it was arc flash and can be repeated by just shorting the 208v high leg and chassis, then the statement by IEEE 1584-2002 standard actually stating that for UNDER 240 VAC (probably should have been AT) fed by a single transformer rated 125 kVA or less, arc flash "need not be considered" is wrong. This was because
what happened to my 208v to neutral short circuit can be considered as single transformers effect since the other terminals didn't encounter short or "arc flash". This was also why I was asking for open delta transformers with two 75kVA transformers, whether you need to add like 75kVA + 35kVA = 110kVA to get the short circuit current of the 208v to neutral short. Because if it does, it can explain why the arc flash occurred because of the huge source short circuit current and after taking the conductor impedances into account, cause the arc flashed. And remember I was sure the third leg is 208v because I had measured with voltmeter between it and neutral and it reads 208v, while others read 120v for first and second terminals to neutral. And in between them 240 volts. BTW.. in USA 208/120v system. It measured 208v between phases. So my 208/120v open delta is not the same as the average US 208/120v system.

The following picture was just reminder of the damage to the breaker lugs. Was it caused by stable arc flash,
unstable arc flash, or just short circuit without arc flash?

Image

Quote:
Quote:
Since most electrical staff put their hands close to the conductors like turning off breakers then during arc flashes. Don't there fingers got burned? And if arc flashed survivors no longer have fingers, how can they work again? In the above picture, note the breaker handles are very close to the terminals. So how can we turn if on or off without the hands close to it (or when inserting the live wire to the terminals in case POCO won't turn off the power due to many paperworks). Do you know of a stick plastic lever to turn the handle off or on?


If you really want to go there, CBS (Circuit Breaker Sales) sells a "chicken switch"...remote operator. But before you do, please review the informational note in 70E:

130.(7)(a) Informational Note #2: “It is the collective experience of the Technical Committee on Electrical Safety in the Workplace that normal operation of enclosed electrical equipment, operating at 600 volts or less, that has been properly installed and maintained by qualified persons is not likely to expose the employee to an electrical hazard.”

They are not saying that it CAN'T happen but that it is highly unlikely that it will. In fact there is an OSHA case of an improper repair at a parking garage where the parking garage attendant flipped the breakers (hopefully SWD rated) at the end of the night and the panel exploded. An electrician had previously just jammed a piece of sheet metal between the breakers and the inner cover to blank off an unused slot. The piece of sheet metal fell out and hit the bus in the distribution panel. The attendant was burned, not killed. But this sort of activity happens thousands of times every day without any injury whatsoever. Which is why for almost the one and only time the 70E Technical Committee actually stuck their necks out.

What I'm trying to get across here and that's also what 70E is stating is that under normal circumstances electrical equipment is safe to operate. The CPSC would never allow electrical equipment in residential applications if it wasn't safe to operate. The exact same equipment is used in commercial systems all the time. Industrial and utility equipment is really not that much different except the sizes and designs change, and we shift from unqualified to qualified workers. Put simply what the 70E Committee is saying in another way is that at least low voltage electrical equipment is not inherently dangerous.

What makes this stuff dangerous is not the equipment itself, nor normal operation of it. It becomes dangerous under two circumstances. As stated either it isn't properly installed or maintained. As it degrades it becomes dangerous to operate. So the first thing you have to do before putting it back into service (NEMA AB-4 speaking here) is to do the inspections and maintenance necessary to put it back safely into service. On miniature and molded case breakers, that's about a 1 minute task. If it's defective you replace it which takes minutes, not hours. And I don't think anyone would have any intention or desire to ever put a molded case breaker back into service that is defective if they know what can happen.

The second circumstance is doing stupid things. Working live when you don't have to. Working live especially when it is obvious that the equipment is already damaged so you should expect the unexpected...when the statement from the 70E Technical Committee no longer applies. Working live without proper protection and training in doing so, particularly when the equipment was never designed and intended for energized work in the first place. And doing a half assed repair. Linemen land cables onto energized lines all the time. They use a "hot line clamp" (google this) to do it. They do it with a hot stick and/or rubber gloves and they do it safely all the time. They do it almost every time they go to de-energize a line too because their work rules require them to install temporary grounding on the line to short all the phases to ground before they perform de-energized work. Often when you remove it, it will draw a pretty impressive looking (but harmless) arc caused by residual voltages that we cannot easily remove. They wear arc flash PPE as well as rubber gloves and leather protectors for doing energized work, sometimes including sleeves that go up to your arm pits. I know because I am trained to do this and I have the same equipment on my truck right now. I do medium voltage (1000 - 35,400 V) work. I have sticks, gloves, sleeves, and ground cluster. I maintain it and I'm trained to use all of it. This is very different from say attempting to land a live service connection on top of an open molded case breaker. You ride the bull bare back, expect to get the horn! Ride 'em cowboy!

Finally when it comes to repairs, this is the actual requirement for ALL electrical repairs whether field or shop: you restore the equipment back to it's original condition.

A rule of thumb for dielectric testing is twice the maximum voltage plus 1,000 V. So for your breaker if it is actually 300 V class (doubtful) we'd apply a 1600 VAC test voltage to it and look for no more than a 1 mA leakage. Or 1.6 megaohms as insulation resistance. If it is 600 V class (most of them are) then this goes up to 2400 VAC and we're looking for 2.4 megaohms or again 1 mA leakage maximum. Motor specs are actually quite a bit higher than this. With molded case breakers the breaker has to be at least 2500 A or larger before repairing it will be less expensive than replacement. But for the equipment that we repair in our shop first we would use dry ice abrasive blasting to remove any and all soot and smoke damage. Depending on circumstances we use denatured alcohol and breaker cleaner to scrub it off in the field or dry ice blasting for larger areas. We'd also replace anything that is structurally damaged. Possibly including welding, grinding, machining, etc., if we can't replace it. Coils get vacuum impregnated with varnish or epoxy (we mostly epoxy these days) then baked to cure. Finally we'd paint metal surfaces with an insulating paint and then test everything to verify it meets standards before sending it back out or energizing it. The acids in smoke often degrade critical items like breakers from the acids in the smoke. The damage often doesn't show up until days or weeks later so when it doubt, replace.

As to what is "enough" insulation or enough clearance...the specifications are testing or performance specifications. There is computer software (again costing thousands) that can estimate clearances but it is really best for testing out ideas, not final results. It reduces the cost of experimental testing for manufacturers but you can't expect it to generate precision results (too many unknowns and variables). So manufacturers build mockups and test them. Then finally they submit samples to the third party testing labs for final certification. You can't possibly do that in the field. So field work relies on one of two approaches. Either we restore back to factory original conditions, or else we use practical rules of thumb that are extremes. For instance a common rule of thumb for 600 V systems is to maintain a separation of at least 3/4" in air, or a minimum of 3/8" with fully insulated barriers. I think you will notice that this is exactly the spacing that the manufacturers also use for the lug spacing on most breakers.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Mon Mar 11, 2019 4:16 pm 

Joined: Wed Feb 20, 2019 3:06 am
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PaulEngr wrote:
Ommi wrote:
These are separate from the vapors, isn't it? Usually vapor only expand for Arc Flash categority 3 or higher?


Don't worry about categories unless you are using the table method for determining PPE in 70E. The key metric is incident energy for electrical calculations or ATPV for PPE ratings.

A piece of textile 12 oz/yard thickness cannot get above ATPV 12. Above that point requires a multilayer approach. PPE Level 3 is 25 cal/cm2 so it has to be multilayer. That's the only difference. Nothing to do with the thermal energy that it is exposed to.

Quote:
PPE is just mostly cotton coverall.


Not true. It's just that treated cotton is about 1/3 of the cost of the next best option so that's mostly what you see.

Kevlar is a brand name of an aramid fiber. Others are Spectra and Nomex. It is optimized for strength and often used for the thread in the cotton PPE (no seam busting). Nomex is a relatively well known brand optimized for flame resistance and that's the main competitor to treated cotton. In recent years there have been some others. For instance Glenguard is a patented modacrylic blend that holds color (hi viz and arc resistant is possible) as well as more chemical resistant.

Quote:
You have mentioned "arc shield". is there small version of this that one can hold and put against the opening of the panel? Theoretically in the industry. What materials are as strong as iron but not conductive and don't melt like plastic. Something that is stronger than leather. Perhaps some kind of fiberglass or kelvar? i just need something to insert in the panel like hand shield for purposes of turning on and off and breakers only for services in the units or room they power. Not for live work. It should be insulator and not a conductor. Hence iron shield and titanium doesn't count. Note this will be used in addition to the normal PPE outfit with long sleeved cotton and head shield, etc.


Arc flash blankets but this is a totally different purpose. These are for containing an arc flash enough to be used in conjunction with 8 cal/cm2 PPE, balaclava and face shield. These are intended for use when escape is impossible (2 second rule doesn't apply) such as down a manhole in a vault. This does not apply to your case.

Quote:
The panel was so full of dusts so just taking precautions in case there would be spontaneous arc flash.


70E does not apply if you do not maintain the equipment properly. In a coal prep plant for instance we routinely have to go in and clean everything top to bottom annually.

But on top of that, read the definition of an arc flash hazard carefully. Arc flash protection is not an ABSOLUTE standard. Spontaneous flash overs do not require PPE which means normal operation of the equipment is not included such as switching tasks. Just walking by isn't included either. As an example did you know that if you are struck by a meteor, you are pretty much dead on the spot? But since this is such a rare event we do not erect meteor shields over parking lots to protect employees as they walk to the buildings. Similarly electrical equipment is generally safe for normal use. It's only when there is something wrong with it or we go to do a task which is inherently dangerous like attempting to land a wire live that we get into a situation where PPE becomes necessary.

Quote:
Also in my last message I was asking about the difference between short circuit with and without arc flash.


That's because short circuits are boring. You will see a jerk of the conductors as they get hit by the high magnetic forces but that's it. Cooper Bussmann's fuseology handbook (free PDF's on their web site) has several videos showing the effects of overduty (exceeding AIC rating) and short circuits. I like using the one with about a 50 foot long cable laying loosely on the floor hit with a very high short current as it goes whipping across the floor.

Quote:
I couldn't find video in youtube where there is continuous short between 120v wire and the chassis. How does it look like?


Uhh, it jerks in a fraction of a second then you usually hear transformer buzzing. That's about it.

Quote:
Would the appearance be like localized welding or does even this simple short can send slug to the hands? Then why is it called Arc Flash Categority 0 (for US residental) when the arms can be injured too. Or this doesn't occur? This is also to tell if what happened in the panel
was just a simple short without any involvement of arc flash. That's why I need to see video what's it like to short circuit 120v to panel in US home setup and doing it continuously. But couldn't find even one video like this. So kindly share one if you have seen one. Thank you.


If you expose some popular synthetic fibers to even the heat of an incandescent light bulb, they will melt onto your skin. We all learned that in the 1970's disco days when this type of material first became popular. Or at least those of us over 40 did. The heat source (light bulb, cigarette lighter, or minor electrical arcing or sparking) itself is relatively harmless...maybe a 1st degree burn, that's it. BUT when the synthetic fibers melt into your skin you will receive a much more severe burn. Natural fibers char instead of melting. Also PPE is designed to keep your skin from exceeding the Stoll curve (at the face/chest area) which is generally considered around 1.2 cal/cm2. The underlayers will see that amount of heat. So what we want to do is to avoid the "work-dry" shirts, hi viz shirts, polypropylene long underwear, and other clothing underneath the PPE that can melt into the skin and do a lot more damage even if we are dressed in the correct PPE.


Finally received the Oberon PPE Cat 2 12cal/cm2 set. The face shield and cap look bigger than the 3M WP96 faceshield (which doesn't have any cap):

Image

Why didn't they make arc flash face shield clearer? It's kinda tinted. You are not looking at welding at all and normal panel. It can diminish the lights and you may need another head mounted lights.

Image

I forgot to ask what are rated Arc Flash PPE underwear or what are you supposed to wear inside the PPE? Can you wear jeans? What do you personally wear underneath Paul? Or must it be worn without any shirt underneath?

Image

Nomex is only aramid, while the above has 65% Modacrylic. Is putting Modacrylic better? Why has it got so many warning about washing with soap, would it affect the "inherently flame resistant" rating, in what way?

Hope you can reply the previous message whether 1 to 2 cycle unstable arc flash can cause injury or vaporize lugs, etc. because I was confused by your last message and just need last clarifications. Thanks a million Paul.



Quote:
As an extreme example Mattisse who is a coworker and all around nice guy I worked with in Philadelphia was wearing a full aluminized fire suit including the gloves. ALSO this was against company rules about meltable materials but since the iron melting area was very dirty, Mattisse wore nitrile gloves underneath the aluminized gloves. One day unknown to him there was a leak in an oxygen line which blew pure oxygen down inside his aluminized fire glove. This lowered the flash point of the nitrile glove until it caught fire essentially at room temperature severely burning his hand inside the aluminized glove. Similar incidents have happened where sleeves catch fire and travel up inside PPE (not wearing head-to-toe) when guys do things like cut the sleeves out in summer time or because they wear their underarmor stuff to stay cool and then get burned inside the PPE.

Level 0 has been deleted as of 2015. As Al Havens who put in the public input that changed it put it, clothing is not PPE.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Mon Mar 11, 2019 5:36 pm 
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Ommi wrote:
Why didn't they make arc flash face shield clearer? It's kinda tinted. You are not looking at welding at all and normal panel. It can diminish the lights and you may need another head mounted lights.

It's an arc FLASH. The light coming off the arc has a lot of UV and can cause retinal damage. The tint protects against that.

Quote:
I forgot to ask what are rated Arc Flash PPE underwear or what are you supposed to wear inside the PPE? Can you wear jeans? What do you personally wear underneath Paul? Or must it be worn without any shirt underneath?


Nonmeltable fibers. Anything you want. You wouldn't for instance want to wear "Under Armour" underneath because it could melt to you from inside the PPE.

Quote:
Nomex is only aramid, while the above has 65% Modacrylic. Is putting Modacrylic better? Why has it got so many warning about washing with soap, would it affect the "inherently flame resistant" rating, in what way?


Nomex is really heavy and hot. Modacrylic is kind of the latest, newest fire retardant textile. I don't know much about it except that it can accept dyes so they can now make for instance arc rated hi viz stuff with it.

Quote:
Hope you can reply the previous message whether 1 to 2 cycle unstable arc flash can cause injury or vaporize lugs, etc. because I was confused by your last message and just need last clarifications.


If the available fault current is high enough, arc gap long enough, or distance is low enough, yes. But that's more of a theoretical question you can answer with IEEE 1584.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Mon Mar 11, 2019 11:40 pm 

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Posts: 45
PaulEngr wrote:
Ommi wrote:
These are separate from the vapors, isn't it? Usually vapor only expand for Arc Flash categority 3 or higher?


Don't worry about categories unless you are using the table method for determining PPE in 70E. The key metric is incident energy for electrical calculations or ATPV for PPE ratings.

A piece of textile 12 oz/yard thickness cannot get above ATPV 12. Above that point requires a multilayer approach. PPE Level 3 is 25 cal/cm2 so it has to be multilayer. That's the only difference. Nothing to do with the thermal energy that it is exposed to.

Quote:
PPE is just mostly cotton coverall.


Not true. It's just that treated cotton is about 1/3 of the cost of the next best option so that's mostly what you see.

Kevlar is a brand name of an aramid fiber. Others are Spectra and Nomex. It is optimized for strength and often used for the thread in the cotton PPE (no seam busting). Nomex is a relatively well known brand optimized for flame resistance and that's the main competitor to treated cotton. In recent years there have been some others. For instance Glenguard is a patented modacrylic blend that holds color (hi viz and arc resistant is possible) as well as more chemical resistant.

Quote:
You have mentioned "arc shield". is there small version of this that one can hold and put against the opening of the panel? Theoretically in the industry. What materials are as strong as iron but not conductive and don't melt like plastic. Something that is stronger than leather. Perhaps some kind of fiberglass or kelvar? i just need something to insert in the panel like hand shield for purposes of turning on and off and breakers only for services in the units or room they power. Not for live work. It should be insulator and not a conductor. Hence iron shield and titanium doesn't count. Note this will be used in addition to the normal PPE outfit with long sleeved cotton and head shield, etc.


Arc flash blankets but this is a totally different purpose. These are for containing an arc flash enough to be used in conjunction with 8 cal/cm2 PPE, balaclava and face shield. These are intended for use when escape is impossible (2 second rule doesn't apply) such as down a manhole in a vault. This does not apply to your case.

Quote:
The panel was so full of dusts so just taking precautions in case there would be spontaneous arc flash.


70E does not apply if you do not maintain the equipment properly. In a coal prep plant for instance we routinely have to go in and clean everything top to bottom annually.

But on top of that, read the definition of an arc flash hazard carefully. Arc flash protection is not an ABSOLUTE standard. Spontaneous flash overs do not require PPE which means normal operation of the equipment is not included such as switching tasks. Just walking by isn't included either. As an example did you know that if you are struck by a meteor, you are pretty much dead on the spot? But since this is such a rare event we do not erect meteor shields over parking lots to protect employees as they walk to the buildings. Similarly electrical equipment is generally safe for normal use. It's only when there is something wrong with it or we go to do a task which is inherently dangerous like attempting to land a wire live that we get into a situation where PPE becomes necessary.

Quote:
Also in my last message I was asking about the difference between short circuit with and without arc flash.


That's because short circuits are boring. You will see a jerk of the conductors as they get hit by the high magnetic forces but that's it. Cooper Bussmann's fuseology handbook (free PDF's on their web site) has several videos showing the effects of overduty (exceeding AIC rating) and short circuits. I like using the one with about a 50 foot long cable laying loosely on the floor hit with a very high short current as it goes whipping across the floor.

Quote:
I couldn't find video in youtube where there is continuous short between 120v wire and the chassis. How does it look like?


Uhh, it jerks in a fraction of a second then you usually hear transformer buzzing. That's about it.

Quote:
Would the appearance be like localized welding or does even this simple short can send slug to the hands? Then why is it called Arc Flash Categority 0 (for US residental) when the arms can be injured too. Or this doesn't occur? This is also to tell if what happened in the panel
was just a simple short without any involvement of arc flash. That's why I need to see video what's it like to short circuit 120v to panel in US home setup and doing it continuously. But couldn't find even one video like this. So kindly share one if you have seen one. Thank you.


If you expose some popular synthetic fibers to even the heat of an incandescent light bulb, they will melt onto your skin. We all learned that in the 1970's disco days when this type of material first became popular. Or at least those of us over 40 did. The heat source (light bulb, cigarette lighter, or minor electrical arcing or sparking) itself is relatively harmless...maybe a 1st degree burn, that's it. BUT when the synthetic fibers melt into your skin you will receive a much more severe burn. Natural fibers char instead of melting. Also PPE is designed to keep your skin from exceeding the Stoll curve (at the face/chest area) which is generally considered around 1.2 cal/cm2. The underlayers will see that amount of heat. So what we want to do is to avoid the "work-dry" shirts, hi viz shirts, polypropylene long underwear, and other clothing underneath the PPE that can melt into the skin and do a lot more damage even if we are dressed in the correct PPE.


I have been researching about this undergarments things for hours and even reading many references such as:

https://www.plantengineering.com/articl ... sh-issues/

Your statements puzzled me. You stated: "Also PPE is designed to keep your skin from exceeding the Stoll curve (at the face/chest area) which is generally considered around 1.2 cal/cm2. The underlayers will see that amount of heat.".

Well. Let's say your PPE has rating of 12cal/m2. And there is an arc flash with incident energy of 12cal/m2. Won't the PPE block the heat? Isn't blocking the heat the quality of the "thermal" protection? If the incident energy is say 6cal/m2. Won't the 12cal/m2 PPE totally blocked it? But you made this puzzling statement: "The underlayers will see that amount of heat.". Then what is the purpose of the PPE when the undergarments can still feel 12cal/m2? It means if you don't wear any undergarments. Then your skin can still feel the 12cal/m2 (which should go to the undergarments)? Or what you are describing where the heat can go to the undergarments only valid when the incident energy is more than the rating of the PPE.. for example 12cal/m2 PPE exposing to 13cal/m2 incident energy where the excess 1cal/m2 will go to the undergarments? Or does 6cal/m2 still go to the undergarments with a 12cal/cm2 PPE and 12cal/cm2 incident energy? If so then the 6cal/m2 into the undergarments or skin can cause 2nd if not 3rd degree burn isn't it? Then how could the 12cal/m2 PPE protect against 12cal/m2 incident energy at all?

Also I read the above url that mentioned: "One of my favorites is that “You don’t have to worry about arc flash below 240 volts.” While it may be true that an arc is more difficult to sustain at lower voltages, there have been some well-documented incidents at 208 V that have resulted in large, sustained arc flashes. This usually requires a very large short circuit available current to sustain the arc.
These types of short circuit currents may be seen in high rise buildings or older commercial buildings where 208 V is used instead of 480 V. Florida Power and Light has a video of one such accident titled, “Once the Arc Begins.” It’s a real eye-opener for people who think there’s no arc flash hazard below 240 V."

Do you know where to find this video "Once the Arc Begins"?

Btw.. my country is the Philippines, we used the same ac system and transformers as the US with the neutral in the centertapped terminals. Hence 120v can be measured between the phases and neutral, and 240v phase to phase in residental homes. While in office or commercial 3 phase open delta, 208v between the high leg delta to neutral and 240v between the phases. We just use phase to phase and never used 120v because we wanted to promote local products and avoided getting 120v appliances in the US (this occurred many decades ago). I heard open delta 3-phase are no longer used in the US? Your 3 phase 208v is between phase to phase, right? Again Our 3 phase 208v is between one phase to neutral and phase to phase is 240v. I'm so aware of this.

Image

The distance between the 3 phase open delta transformers (75kVA) and my building service entrance is about 20 feet. There is no main breaker or overcurrent protection device between the transformers and the arc flashed breakers (one of the 4 disconnects in the panel. The POCO wires go to the gutter first, then 4 service meters then 4 disconnect/breakers (where one of them arc flashed)). This could increase the incident energy, isn't it. The wiring used by the pole is about 1/0 AWG. My service entrance conductor size is bigger.

But the big puzzle is the research that arc flash can't sustain for 208v. You stated:

Quote:

In addition at 480 V most of the arc flash testing is done with 1/2" to 1" arc gaps, venturing into longer arc gaps only with extremely high fault currents because arc flash testing is done with stable arcs (arc instability is hard to predict). But the original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result. All the other 208 V results failed because they never got to a stable arc. The original testing used 1/2" arc gaps. The new test data set used to develop IEEE 1584-2018 includes 1/4" gaps and used much thinner "fuse" wires to get stable arcing to occur down to 208 VAC. The obvious consequence here is that it is nearly impossible to have a stable arc at 1/2" (12 mm). Stable 208 V arcs are very short, closer to 10-15 mm at most. But going back to our arc flash energy this also means greatly reduced arcing energy. Try it with the web site you used. You'll see a dramatic reduction with a 4 mm arc gap, never mind a 2 mm arc gap.


Let's focus on this in our conclusion (I know this thread is very long so need to conclude it asap). You said "original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result.". Any reference or paper about this I can read. At what bolted short circuit current was the test done? I want to know if the stable 208v arc with 1/2" gap can cause the following damage. Do you think the following is really arc flash damage or just short circuit where conductor and lugs melted from the over current without any arc flash (can this really happen at all?? Kindly answer this as this is the last thing I wanna know before I move on. So many thanks to you Paul!)?

Image

Quote:

As an extreme example Mattisse who is a coworker and all around nice guy I worked with in Philadelphia was wearing a full aluminized fire suit including the gloves. ALSO this was against company rules about meltable materials but since the iron melting area was very dirty, Mattisse wore nitrile gloves underneath the aluminized gloves. One day unknown to him there was a leak in an oxygen line which blew pure oxygen down inside his aluminized fire glove. This lowered the flash point of the nitrile glove until it caught fire essentially at room temperature severely burning his hand inside the aluminized glove. Similar incidents have happened where sleeves catch fire and travel up inside PPE (not wearing head-to-toe) when guys do things like cut the sleeves out in summer time or because they wear their underarmor stuff to stay cool and then get burned inside the PPE.

Level 0 has been deleted as of 2015. As Al Havens who put in the public input that changed it put it, clothing is not PPE.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Tue Mar 12, 2019 3:44 am 
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Ommi wrote:
I have been researching about this undergarments things for hours and even reading many references such as:

https://www.plantengineering.com/articl ... sh-issues/

Your statements puzzled me. You stated: "Also PPE is designed to keep your skin from exceeding the Stoll curve (at the face/chest area) which is generally considered around 1.2 cal/cm2. The underlayers will see that amount of heat.".

Well. Let's say your PPE has rating of 12cal/m2. And there is an arc flash with incident energy of 12cal/m2. Won't the PPE block the heat? Isn't blocking the heat the quality of the "thermal" protection? If the incident energy is say 6cal/m2. Won't the 12cal/m2 PPE totally blocked it? But you made this puzzling statement: "The underlayers will see that amount of heat.". Then what is the purpose of the PPE when the undergarments can still feel 12cal/m2? It means if you don't wear any undergarments. Then your skin can still feel the 12cal/m2 (which should go to the undergarments)? Or what you are describing where the heat can go to the undergarments only valid when the incident energy is more than the rating of the PPE.. for example 12cal/m2 PPE exposing to 13cal/m2 incident energy where the excess 1cal/m2 will go to the undergarments? Or does 6cal/m2 still go to the undergarments with a 12cal/cm2 PPE and 12cal/cm2 incident energy? If so then the 6cal/m2 into the undergarments or skin can cause 2nd if not 3rd degree burn isn't it? Then how could the 12cal/m2 PPE protect against 12cal/m2 incident energy at all?


Not sure about 12 cal/m2. I know cal/cm2 is a very strange mixed English/SI unit. It's historical. IEEE 1584 uses J/cm2 to be 100% SI.

First off Alicia Stoll is famous because she did a series of experiments where she exposed volunteers to undergo an experiment in which she exposed a small 1 cm round circle (roughly a cigarette burn) to a calibrated heat source and also to a copper bomb calorimeter and examined the result. She was able to determine the threshold heat necessary to cause a second degree burn. Her experiment was run at different time intervals down to 1 second. The great thing about her experiment is that because of what she did we can now predict the onset of a second degree burn by simply measuring it with a copper bomb calorimeter rather than testing it with live subjects. The result is 1.2 cal/cm2 at 1 second and slowly increases to about 2 cal/cm2 at extended times. For the purposes of NFPA 70E we just use a flat 1.2 cal/cm2 rather than adjusting for time for considering protection without PPE.

ASTM 1959 is used to test the fabric, not the whole PPE. This is something of a technicality but when they actually test the fabric they cut squares of test material and place it in front of a series of copper calorimeters mounted at various distances from the arc source as well as a control (unprotected). The cloth samples are essentially protecting the calorimeters. I think there are about 30 samples used. Then they set off the arc and record the arc current as well as the measurements of heat seen by each of the calorimeters. Then they physically examine each piece of fabric to see if it broke open. Then they take the measured heat as seen by the copper calorimeters and compare it to the Stoll curve. If the heat crosses the Stoll curve at any point (the test is run for several seconds) it fails. If it is under the Stoll curve, it passes. Then the combined pass/fail results are plotted (incident energy vs. pass/fail) and some math is applied to calculate the threshold at which it fails. The combined ATPV rating is the lower of the two results. Generally rainwear fails the breakopen test first and uniform type material fails the thermal test first.

Moving forward to your question then essentially we want to dress as "PPE Level 0" which means nonmeltable clothing. Realistically based on Stoll's tests you could be naked inside the PPE and still come away with no more than a second degree burn but actual testing has shown much better results than the test would predict in reality. Some relatively minor injuries on the hands and arms like we would expect but effectively victims walk away. There are MANY details about both the ASTM 1959 and IEEE 1584 standards as well as the NFPA 70E implementation of it that basically make the whole thing extremely contrived. If you look or think about it long enough you can poke giant gaping holes in the theory. But we can also be assured that after over 2 decades of "field testing", it works, even if the theory that it rests on is extremely weak.

As to the issue of calculating something "underneath", don't try that. It doesn't work very well. The problem is that ATPV is not additive. If I wear say an ATPV 8 shirt and pants and then another ATPV 8 coveralls over that, I won't just get ATPV 16. Actually it usually turns out far better because the trapped air layer between the two layers of PPE contributes to the ATPV rating. This is similar to why layering works much better with winter clothing than it does with a single much thicker layer.

Arcwear does a lot of 2 layer testing. Utilities like this because it allows their employees to wear their standard (usually 8-12 ATPV) work uniforms and then simply throw on a much lighter pair of coveralls or winter jackets and overalls to achieve higher ratings. They also ask them if they would volunteer to release the data publicly and many agree to this. You can see the data here:

https://www.arcwear.com/resources/2-lay ... esults.php

Arcwear uses the manufacturer of the fabric in the table. So you need to know for instance that "Carhartt" uses Milliken Mills fabric. PPE suppliers have their own layering charts you can use, too. This doesn't say much with your base layer question except to say that you won't exceed the Stoll curve if you are naked under an ATPV 12 PPE and it gets exposed to a 12 cal/cm2 incident energy. If you add a nonmeltable underlayer of clothing under that the final result will be higher than ATPV 12. Ignition of the underlayers doesn't seem to be an issue at the Stoll curve but we don't consider whether or not the underlayers are contributing to the final ATPV rating if they are not arc rated. The big concern though is that meltable fabrics like polypropylene WILL melt under the PPE so you want to stay away from that.

Quote:
Do you know where to find this video "Once the Arc Begins"?


No.

Quote:
Btw.. my country is the Philippines, we used the same ac system and transformers as the US with the neutral in the centertapped terminals. Hence 120v can be measured between the phases and neutral, and 240v phase to phase in residental homes. While in office or commercial 3 phase open delta, 208v between the high leg delta to neutral and 240v between the phases. We just use phase to phase and never used 120v because we wanted to promote local products and avoided getting 120v appliances in the US (this occurred many decades ago). I heard open delta 3-phase are no longer used in the US? Your 3 phase 208v is between phase to phase, right? Again Our 3 phase 208v is between one phase to neutral and phase to phase is 240v. I'm so aware of this.


It is very common to use a single phase center tapped 120/240 V transformer and a second 240 V transformer in a broken delta as a cheap 3 phase source for small loads such as HVAC. Or for better efficiency and larger loads the utility might use 3 pole mounted transformers either in a wye (208/120) or corner grounded delta (240 V). What has fallen out of favor is two things. First, ungrounded deltas have fallen out of favor due to problems with transients EXCEPT that U.S. Navy requires it and sometimes in instrumentation in switchgear. Second corner grounded deltas with 120 V taps are a real issue too because the common Edison style 120/240 single phase sources have only one 120 V source and a neutral so they lead to really unbalanced loads and confused electricians. Utilities love wye-wye because it's cheaper than delta-wye. Industrials love delta-wye because they don't like to be the ground source for the utilities.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Tue Mar 12, 2019 7:45 am 

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Posts: 45
PaulEngr wrote:
The current determines the arc energy flux (power) for the most part. The time determines the energy released. And there is one more critical factor: arc gap. Arc flash testing at 480 V usually uses arc gaps in the 1/2" to 1" range. At 208 V it is hard to get an arc to be self sustaining with an arc gap over 1/4". At 120 VAC we're starting to look at a couple millimeters at most (arc welding distances). With such a small arc length, flux (arc power) is constrained by the short arc gap. So I'm not sure what assumptions you used in your calculation but you need to be setting a reasonable arc gap, too, and 25 mm is not it.

Going a little further, the wiring used for low voltage distribution and controls is usually mostly #12 or #14. It occasionally gets to #10 for voltage drop reasons. Despite the ampacities, NEC rules actually set much more breaker sizes for smaller wiring in residential and commercial use. For instance #14 at 75 C has an ampacity of 20 A but the breaker size is specified as 15 A. Except for appliance circuits, laundry, and recently a garage circuit, residential breakers and receptacles are all 15 A. Magnetic trips are usually set at most to 10 times the thermal trip setting or 150 A. And you were just calculating short circuits into the thousands of amps. So clearly we are going to trip "instantaneously" for the vast majority of commercial/residential loads. With miniature breakers they usually trip in under 1 cycle (0.016 s). Both dual element and fast blow fuses are going to trip in 1/4 cycle (0.004 seconds) under these conditions.

In addition at 480 V most of the arc flash testing is done with 1/2" to 1" arc gaps, venturing into longer arc gaps only with extremely high fault currents because arc flash testing is done with stable arcs (arc instability is hard to predict). But the original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result. All the other 208 V results failed because they never got to a stable arc. The original testing used 1/2" arc gaps. The new test data set used to develop IEEE 1584-2018 includes 1/4" gaps and used much thinner "fuse" wires to get stable arcing to occur down to 208 VAC. The obvious consequence here is that it is nearly impossible to have a stable arc at 1/2" (12 mm). Stable 208 V arcs are very short, closer to 10-15 mm at most. But going back to our arc flash energy this also means greatly reduced arcing energy. Try it with the web site you used. You'll see a dramatic reduction with a 4 mm arc gap, never mind a 2 mm arc gap.

So I'm telling you that most of the time and almost all circumstances when working with low voltage (<300 V) systems, arc flash is simply not a serious issue. In fact it is so minor of an issue that the IEEE 1584-2002 standard actually stated that for UNDER 240 VAC (probably should have been AT) fed by a single transformer rated 125 kVA or less, arc flash "need not be considered". In fact that describes your scenario. And some testing done at PG&E (a utility) published back then even showed that arcs would extinguish at those voltages in 1 to 2 cycles. They only got a single test case at 208 VAC with the highest available fault current to work in the tests that were used to develop the original IEEE 1584-2002 equations. In fact with around 15 years of active research on arc flash, it took until 2009 before there was even a recorded fatality. Think about that...15-20 years straight with more electricians working on 240/120 and 208/120 systems without a single arc flash fatality. With all the engineering above you can probably see why this is an almost impossible situation.

Now let's consider human behavior a little bit at this point. Have you ever observed residential and controls technicians working on distribution panels? They scare those of us that work industrial and large commercial operations. They just open everything up and start moving energized wires around, leaving them hanging out exposed, never shut off a breaker, you name it. How about disconnecting a load? Just yank the plug out of the receptacle, energized or not. On a breaker, same thing. Just lift the hot. LOTO? What are you talking about? Have you actually seen what passes for a "lockout device" on a distribution panel? It's a joke. But there's a reason for it. The slowest breaker in the panel is going to be the main distribution panel breaker and that one is still going to be in the 1-2 cycle trip speed range. It has to trip slower than the 15 and 20 A breakers that it is feeding but that's it. It might still trip as fast as the smaller breakers but something called dynamic resistance comes into play which allows breakers to trip almost at the same speed and still coordinate properly. Want to know what happens if an "arc flash" happens in this environment? Ask around. You'll get the guy that tells you about the time that he accidentally touched a hot wire to the neutral or ground bar energized when he wasn't supposed to. So he used the standard electrician's first aid kit...wrapping his fingers in electrical tape so that the foreman wouldn't see the blisters. Is this going to be the extent of the injury? I think you should know by now that I can't guarantee it but trust me. My grandfather was an electrician for the telephone company, back when there was only one. My dad and grandfather did all kinds of electrical work on the farm where I grew up. I know what goes on because I've done it myself. I know exactly how many guys have gotten injured or killed doing this. Because when we started getting serious about arc flash it was thought that there was no risk at the voltages you are dealing with. In fact it took decades for someone to get killed doing it. I know because I've gone through hundreds of OSHA reports doing some research on subjects like this for a former employer. We had the same kinds of questions about low voltage. That's when I uncovered the 2009 OSHA case. And that's where we're going to next.

Lets step up to the utility side of things. The utility fuse or breaker must trip slower than the main in the distribution panel. AND the utility fuse or breaker is not seeing the 15 kA worth of fault current you calculated on the secondary side. It's seeing the fault current on the primary side. So even with a very low 480 V distribution voltage, it is seeing less than half the fault current. At higher voltages (say 4160 V), the fault current is less than 10% of what you calculated. On top of that, the inrush on your 2% impedance transformer is extremely high. So the cutout fuse out of necessity must be designed to either operate slowly or sized to be so large that it only reacts to short circuits. So it offers you almost no protection whatsoever on the secondary side except for removing dead shorted services from the system. Linemen know this. That's why they operate the cutout with a hot stick and work at glove distance on everything even if it's "only" 208/120. So going back to our assumptions, IF we can get a stable arc, we can certainly get a significant arc flash. They finally demonstrated that it can happen in laboratory conditions in the last 10 years, and an electrician in Georgia "proved" it can happen in 2009. Two electricians were assigned to remove a temporary construction panel. They were dressed in standard work attire for summer work in Georgia for residential electricians, flip flops, shorts, and tank tops (this was actually mentioned in the OSHA report). They decided that they didn't want to wait for the lineman to arrive so they began disassembling the live distribution panel. Something happened (not documented in OSHA's summary) that caused an arc flash. I don't know what happened for sure but I can guess that it is probably something very much like the incident that happened twice at your facility. Both electricians went to the hospital and one of them died from injuries a couple days later. Can I be any more clear about the consequences than this?



Well. 208v arc flash is so rare even for IEEE (they had only 1 case) so hope they can take my case as example of low voltage 208v arc flash.

After looking at more pictures. I think it is 3 phase arc flash that involves all 3 phases (the other 2 just minor):

This was taken a day after the incident in 2015 inside my car:

Image

Even the 1st lugs were affected. What could have happened was there was first a major arc flash between the
208v high leg and chassis (which even put a hole at chassis (drawn in green below) then it enveloped the area with so much heat, it progressed into 3 phase arc flash injuring the electrician arms sending him to the burn clinic:

Image

The following with cardboard removed showing the chassis at back of first terminal was affected suggesting a 3 phase arc flash. The right chassis portion was painted.

Image

How does one contact the IEEE committee? Do they accept 208v arc flash cases in other countries (especially one where the USA has duplicate power system they created nearly 50 years ago)? Who is IEEE committee here. Let it become an example of a 3-phase open delta arc flash case involving 208v (in which they had only one case so far only (?)).

An EE confirmed it was arc flashed. He told me:

"If you see blackening on surfaces above the destruction, it can be caused by long burning, by smoke-soot which lasted many seconds/minutes, without any plasma-explosion.
But if you see blackening on surfaces to the side and/or below, that's caused by "metal-black," pure metal-powder which was condensed out of a blazing bright plasma of arcflash.
Didn't the electrician report a huge flash of light and a loud buzz sound? If they were burned but not electrically shocked, that was from skin contacting the plasma in the arcflash, which is usually far hotter than any flame. (The arc-plasma mostly made of metal-vapor, incandescent gas heated far above the boiling point of molten copper or aluminum.)
In your top picture, the blackening is to the side (so not caused by many minutes of rising smoke,) and it has radial lines from explosive trajectory of gas and metal particles. Almost certainly there was a large plasma (arc flash,) many inches across if not larger. Where it touched cold metal, the vaporized metal inside the flash would condense, forming pure-metal "soot."
Metal nano-powder is typically colored black. Copper, aluminum, even etc., creates a light-absorbing black soot when its particles are fine enough. No carbon needed, the black stuff is pure copper or aluminum. You can buy "platinum black" or "copper black" from chemistry suppliers, which is simply ultra-fine pure metal powder."


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Tue Mar 12, 2019 8:41 am 
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Ommi wrote:
Do you know where to find this video "Once the Arc Begins"?


I can guess. I believe at least part of FP&L was purchased by Progress Energy which was subsequently purchased by Duke Energy. I would try with them. It's not easy. It's a huge organization. Most of my contacts (former Progress Energy) have retired or left the company after the merger.

Quote:
Let's focus on this in our conclusion (I know this thread is very long so need to conclude it asap). You said "original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result.". Any reference or paper about this I can read. At what bolted short circuit current was the test done? I want to know if the stable 208v arc with 1/2" gap can cause the following damage. Do you think the following is really arc flash damage or just short circuit where conductor and lugs melted from the over current without any arc flash (can this really happen at all?? Kindly answer this as this is the last thing I wanna know before I move on. So many thanks to you Paul!)?


Try this one:

https://drive.google.com/open?id=0B6mGR ... Dl5VzlDSWM

It's getting a little old but it's still just about everything that's out there. I believe a more recent Battcon paper got published (DC only) but that's the only significant one. There are several papers referenced in there. I tried to use the more "public" (not IEEE owned) papers when possible.

As I understand it there was a strong belief early on that arc flash below 250-300 VAC simply wasn't significant enough to worry about. I don't think I included the PG&E test data in the paper above and you don't really need it but suffice to say that the PG&E test showed that arcs extinguished below 250 VAC in 1 to 2 cycles under almost all conditions and led to the original IEEE 1584-2002 statement about 208 V and below and fed by a transformer sized under 125 kVA. Then evidence started to show up in other cases. For instance some barrier tests (paper is in the article above) showed something different. In other words if you watched the video Jim Philips put out about the IEEE 1584-2018 edition, they were wrong. As he stated, testing done by the joint IEEE/NFPA task force revealed that arc flash above 1.2 cal/cm2 was possible below 240 VAC. The testing they did largely duplicated the tests that are in the papers linked above so even though IEEE hasn't published all the test data, you don't really need it. So the IEEE 1584 committee revised the 2018 standard to state that the new cutoff is 2 kA. They switched from a transformer size to short circuit to get away from arguments about impedance, different configurations, etc. The tests that reveal a problem are of course extreme examples such as a VCBB configuration which means that you have vertical bus bars terminating into a solid insulating barrier, kind of like what you get on top of a circuit breaker.

The best solution of course would be if we could also predict when arcs are unstable and self-extinguish. So that for instance if I have all the inputs for the IEEE 1584-2018 model, I could then calculate that under certain circumstances an arc would be unstable. No such formula exists. From all the data I've been able to assemble I don't see any pattern to it either. Marcia Eblen published some new material where she made a stab at it and I can honestly say it really isn't much more than a "stab at it" either. She has been intimately involved in a lot of the testing for utilities and I have a lot of respect for her abilities. At best we can upper bound some things and that's what the above paper tried to do using existing standards. Obviously in light of the updated IEEE 1584, the "PPE Level 0" category has shrank considerably which means that the PPE Level 1 category which depends on the NESC standard has grown considerably downward.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Tue Mar 12, 2019 6:19 pm 

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Posts: 45
PaulEngr wrote:
Ommi wrote:
Do you know where to find this video "Once the Arc Begins"?


I can guess. I believe at least part of FP&L was purchased by Progress Energy which was subsequently purchased by Duke Energy. I would try with them. It's not easy. It's a huge organization. Most of my contacts (former Progress Energy) have retired or left the company after the merger.

Quote:
Let's focus on this in our conclusion (I know this thread is very long so need to conclude it asap). You said "original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result.". Any reference or paper about this I can read. At what bolted short circuit current was the test done? I want to know if the stable 208v arc with 1/2" gap can cause the following damage. Do you think the following is really arc flash damage or just short circuit where conductor and lugs melted from the over current without any arc flash (can this really happen at all?? Kindly answer this as this is the last thing I wanna know before I move on. So many thanks to you Paul!)?


Try this one:

https://drive.google.com/open?id=0B6mGR ... Dl5VzlDSWM

It's getting a little old but it's still just about everything that's out there. I believe a more recent Battcon paper got published (DC only) but that's the only significant one. There are several papers referenced in there. I tried to use the more "public" (not IEEE owned) papers when possible.

As I understand it there was a strong belief early on that arc flash below 250-300 VAC simply wasn't significant enough to worry about. I don't think I included the PG&E test data in the paper above and you don't really need it but suffice to say that the PG&E test showed that arcs extinguished below 250 VAC in 1 to 2 cycles under almost all conditions and led to the original IEEE 1584-2002 statement about 208 V and below and fed by a transformer sized under 125 kVA. Then evidence started to show up in other cases. For instance some barrier tests (paper is in the article above) showed something different. In other words if you watched the video Jim Philips put out about the IEEE 1584-2018 edition, they were wrong. As he stated, testing done by the joint IEEE/NFPA task force revealed that arc flash above 1.2 cal/cm2 was possible below 240 VAC. The testing they did largely duplicated the tests that are in the papers linked above so even though IEEE hasn't published all the test data, you don't really need it. So the IEEE 1584 committee revised the 2018 standard to state that the new cutoff is 2 kA. They switched from a transformer size to short circuit to get away from arguments about impedance, different configurations, etc. The tests that reveal a problem are of course extreme examples such as a VCBB configuration which means that you have vertical bus bars terminating into a solid insulating barrier, kind of like what you get on top of a circuit breaker.

The best solution of course would be if we could also predict when arcs are unstable and self-extinguish. So that for instance if I have all the inputs for the IEEE 1584-2018 model, I could then calculate that under certain circumstances an arc would be unstable. No such formula exists. From all the data I've been able to assemble I don't see any pattern to it either. Marcia Eblen published some new material where she made a stab at it and I can honestly say it really isn't much more than a "stab at it" either. She has been intimately involved in a lot of the testing for utilities and I have a lot of respect for her abilities. At best we can upper bound some things and that's what the above paper tried to do using existing standards. Obviously in light of the updated IEEE 1584, the "PPE Level 0" category has shrank considerably which means that the PPE Level 1 category which depends on the NESC standard has grown considerably downward.


Thanks for the paper above. Everything finally started to make sense. My arc flash breakers was enclosed in small panel with the vertical not even more than one foot:

Image

It was photo taken before the arc flash breaker was put at the back where the live line wires were transferred to it. The third wire was at back of the first wire so it was not visible in the picture.

It fulfilled this passage in the paper:

"In their testing without a barrier at 208 V, “arcing could not be sustained at 10 kA or less, even with the shortest (12.7
mm) gap.” A 250 V test with 13 kA of arcing current and a 12.7 mm gap extinguished at 21 ms. With a barrier, arcs were sustained down to 4.5 kA at 208 V with a 12.7 mm gap. At 32 mm arcs could not be sustained below 10 kA. Measured incident energies with the 12.7 mm gap with a 0.1 second arc and 22 kA bolted current were 2.7 cal/cm2 and it increased to 3.2 cal/cm2 for the 32 mm gap case at 22 kA. In these tests a breaker was set to open at 0.1 s so whether arcing could be sustained beyond 6 cycles is unknown."

Remember I don't have any breaker upstream of it that can decrease the incident energy:

I read https://brainfiller.com/2018/12/19/2018 ... n-deleted/

"125 kVA – Going, going, gone!
After much speculation about the fate of the 125 kVA transformer “exception”, the 2018 Edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has finally been published and made it official. The 125 kVA transformer exception has been deleted!
In its place is the new language:
“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”
What Happened?
The original language is from the 2002 Edition of IEEE 1584. It was based on a few tests that indicated sustaining an arc flash at lower levels of short circuit current and lower voltage would be unlikely due to a limited conducting plasma and limited voltage to support the arc. The original 2002 language stated:
“Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply”"

Well. Instead of just “Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A” in the new 1584-2018.

The following must be added:

"Unless the panel is small in which case arcs can sustain enough to cause injury in the arms (at least) with higher incident energy"

IEEE 1584-2018 was just created 4 months ago. How could we let them add the above passage (or kinda like it)??


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Tue Mar 12, 2019 10:10 pm 

Joined: Wed Feb 20, 2019 3:06 am
Posts: 45
Ommi wrote:
PaulEngr wrote:
Ommi wrote:
Do you know where to find this video "Once the Arc Begins"?


I can guess. I believe at least part of FP&L was purchased by Progress Energy which was subsequently purchased by Duke Energy. I would try with them. It's not easy. It's a huge organization. Most of my contacts (former Progress Energy) have retired or left the company after the merger.

Quote:
Let's focus on this in our conclusion (I know this thread is very long so need to conclude it asap). You said "original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result.". Any reference or paper about this I can read. At what bolted short circuit current was the test done? I want to know if the stable 208v arc with 1/2" gap can cause the following damage. Do you think the following is really arc flash damage or just short circuit where conductor and lugs melted from the over current without any arc flash (can this really happen at all?? Kindly answer this as this is the last thing I wanna know before I move on. So many thanks to you Paul!)?


Try this one:

https://drive.google.com/open?id=0B6mGR ... Dl5VzlDSWM

It's getting a little old but it's still just about everything that's out there. I believe a more recent Battcon paper got published (DC only) but that's the only significant one. There are several papers referenced in there. I tried to use the more "public" (not IEEE owned) papers when possible.

As I understand it there was a strong belief early on that arc flash below 250-300 VAC simply wasn't significant enough to worry about. I don't think I included the PG&E test data in the paper above and you don't really need it but suffice to say that the PG&E test showed that arcs extinguished below 250 VAC in 1 to 2 cycles under almost all conditions and led to the original IEEE 1584-2002 statement about 208 V and below and fed by a transformer sized under 125 kVA. Then evidence started to show up in other cases. For instance some barrier tests (paper is in the article above) showed something different. In other words if you watched the video Jim Philips put out about the IEEE 1584-2018 edition, they were wrong. As he stated, testing done by the joint IEEE/NFPA task force revealed that arc flash above 1.2 cal/cm2 was possible below 240 VAC. The testing they did largely duplicated the tests that are in the papers linked above so even though IEEE hasn't published all the test data, you don't really need it. So the IEEE 1584 committee revised the 2018 standard to state that the new cutoff is 2 kA. They switched from a transformer size to short circuit to get away from arguments about impedance, different configurations, etc. The tests that reveal a problem are of course extreme examples such as a VCBB configuration which means that you have vertical bus bars terminating into a solid insulating barrier, kind of like what you get on top of a circuit breaker.

The best solution of course would be if we could also predict when arcs are unstable and self-extinguish. So that for instance if I have all the inputs for the IEEE 1584-2018 model, I could then calculate that under certain circumstances an arc would be unstable. No such formula exists. From all the data I've been able to assemble I don't see any pattern to it either. Marcia Eblen published some new material where she made a stab at it and I can honestly say it really isn't much more than a "stab at it" either. She has been intimately involved in a lot of the testing for utilities and I have a lot of respect for her abilities. At best we can upper bound some things and that's what the above paper tried to do using existing standards. Obviously in light of the updated IEEE 1584, the "PPE Level 0" category has shrank considerably which means that the PPE Level 1 category which depends on the NESC standard has grown considerably downward.


Thanks for the paper above. Everything finally started to make sense. My arc flash breakers was enclosed in small panel with the vertical not even more than one foot:

Image

It was photo taken before the arc flash breaker was put at the back where the live line wires were transferred to it. The third wire was at back of the first wire so it was not visible in the picture.

It fulfilled this passage in the paper:

"In their testing without a barrier at 208 V, “arcing could not be sustained at 10 kA or less, even with the shortest (12.7
mm) gap.” A 250 V test with 13 kA of arcing current and a 12.7 mm gap extinguished at 21 ms. With a barrier, arcs were sustained down to 4.5 kA at 208 V with a 12.7 mm gap. At 32 mm arcs could not be sustained below 10 kA. Measured incident energies with the 12.7 mm gap with a 0.1 second arc and 22 kA bolted current were 2.7 cal/cm2 and it increased to 3.2 cal/cm2 for the 32 mm gap case at 22 kA. In these tests a breaker was set to open at 0.1 s so whether arcing could be sustained beyond 6 cycles is unknown."

Remember I don't have any breaker upstream of it that can decrease the incident energy:

I read https://brainfiller.com/2018/12/19/2018 ... n-deleted/

"125 kVA – Going, going, gone!
After much speculation about the fate of the 125 kVA transformer “exception”, the 2018 Edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has finally been published and made it official. The 125 kVA transformer exception has been deleted!
In its place is the new language:
“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”
What Happened?
The original language is from the 2002 Edition of IEEE 1584. It was based on a few tests that indicated sustaining an arc flash at lower levels of short circuit current and lower voltage would be unlikely due to a limited conducting plasma and limited voltage to support the arc. The original 2002 language stated:
“Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply”"

Well. Instead of just “Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A” in the new 1584-2018.

The following must be added:

"Unless the panel is small in which case arcs can sustain enough to cause injury in the arms (at least) with higher incident energy"

IEEE 1584-2018 was just created 4 months ago. How could we let them add the above passage (or kinda like it)??


To add to the above comments. Reading the paper on 2nd and 3rd time and pondering on it. It was not really the panel sizes that were the factor (unless using meter enclosure that is so small because in the open tests it used one like my panel size) but whether the rods were suspended in open air without any barrier (or breakers). Why did IEEE do the 300 tests by leaving the cooper rods or wires floating in open space which were not representative of real panel with real breakers (with the top acting like barriers). What were they thinking? The IEEE tests done were flawed when taking low voltage arc flash into account (Say, do switch gears or high voltage panels have empty spaces where the cooper tend to be hanging? How?) The paper described the barrier configuration which made so much sense as the barrier focuses the arc and incident energy to injuring proportions. Here it was described so well:

"This test uses two additional equipment configurations compared to the IEEE “standard”
configurations. The first configuration is called a barrier. Rather than leaving the copper bus bars
floating in open space like previous tests, the bus bars are “terminated” into a block of solid insulating
material such as phenolic. This is representative of the lugs on the line side of many types of equipment
such as molded case circuit breakers, and also representative of enclosures where the bus bars are
secured at one end by solid material. In this configuration the arc “plasma” tends to pool at the barrier
and jet outward, strongly increasing the incident energy as well as helping to stabilize low voltage arcs.
The second configuration is a “chamber” where part of the bus bar is enclosed in a small box within the
larger standard IEEE enclosure that is open on one side. Chambers simulate congested wireways such
as conditions where bus bars are mounted inside a lighting panel behind the circuit breakers. A chamber
both partly reflects thermal radiation as well as constraining air flow so that arcing is more stable than a
more open condition.

Arcs were not sustained at 2 kA under any conditions at a gap of 25.4 mm or up to 7 kA using IEEE
standard test conditions (copper rods mounted veritcally hanging in a “chamber” or a box within a
box). Terminating the rods into a phenolic barrier allowed sustained arcing at 4 kA and using aluminum
or bars instead of rods allowed sustained arcing at 4 kA. Tests at 218 V and 250 V also showed much
more stable arcing, indicating that 208 V may be something of a limiting factor."

Therefore instead of the new IEEE 1584-2018 edition using this statement:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”

The "barrier" data must be integrated to the above.

How do you properly rephrase it?

Or could the barrier experiments be flawed in some way too?


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Wed Mar 13, 2019 4:56 am 

Joined: Wed Feb 20, 2019 3:06 am
Posts: 45
Quote:
To add to the above comments. Reading the paper on 2nd and 3rd time and pondering on it. It was not really the panel sizes that were the factor (unless using meter enclosure that is so small because in the open tests it used one like my panel size) but whether the rods were suspended in open air without any barrier (or breakers). Why did IEEE do the 300 tests by leaving the cooper rods or wires floating in open space which were not representative of real panel with real breakers (with the top acting like barriers). What were they thinking? The IEEE tests done were flawed when taking low voltage arc flash into account (Say, do switch gears or high voltage panels have empty spaces where the cooper tend to be hanging? How?) The paper described the barrier configuration which made so much sense as the barrier focuses the arc and incident energy to injuring proportions. Here it was described so well:

"This test uses two additional equipment configurations compared to the IEEE “standard”
configurations. The first configuration is called a barrier. Rather than leaving the copper bus bars
floating in open space like previous tests, the bus bars are “terminated” into a block of solid insulating
material such as phenolic. This is representative of the lugs on the line side of many types of equipment
such as molded case circuit breakers, and also representative of enclosures where the bus bars are
secured at one end by solid material. In this configuration the arc “plasma” tends to pool at the barrier
and jet outward, strongly increasing the incident energy as well as helping to stabilize low voltage arcs.
The second configuration is a “chamber” where part of the bus bar is enclosed in a small box within the
larger standard IEEE enclosure that is open on one side. Chambers simulate congested wireways such
as conditions where bus bars are mounted inside a lighting panel behind the circuit breakers. A chamber
both partly reflects thermal radiation as well as constraining air flow so that arcing is more stable than a
more open condition.

Arcs were not sustained at 2 kA under any conditions at a gap of 25.4 mm or up to 7 kA using IEEE
standard test conditions (copper rods mounted veritcally hanging in a “chamber” or a box within a
box). Terminating the rods into a phenolic barrier allowed sustained arcing at 4 kA and using aluminum
or bars instead of rods allowed sustained arcing at 4 kA. Tests at 218 V and 250 V also showed much
more stable arcing, indicating that 208 V may be something of a limiting factor."

Therefore instead of the new IEEE 1584-2018 edition using this statement:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A”

The "barrier" data must be integrated to the above.

How do you properly rephrase it?

Or could the barrier experiments be flawed in some way too?


Image

Btw.. how did IEEE 1584-2018 test the above in their 300 testing experiments. Any reference of how they exactly did it? Like did they short the 3 conductors and then turn on the main breaker to initiate the arc flash?

With 208v tests. 1 out of 300. One IEEE 1584 test case achieved a sustained arcing fault at 87 kA with a 12.7 mm gap. The rest fizzled.
When barrier (or akin to breaker) was put. arcs were sustained down to 4.5 kA at 208 V with a 12.7 mm gap. This was quite low and likely what happened to my electrician arc flash incident in 2015.

In IEEE 1584-2018. Have they officially acknowledged the barrier tests and the data, or is there still some controversy or uncertainty about it.

208v arc flash is said to be rare in the US. How come. In office or commercial. How often do you use 208v 3 phase. Does the open delta configuration produce more short circuit current than integrated 3 phase transformers? What kind of panels were the breakers installed. Maybe no one was stupid to land any live wire to the breaker input terminal like what my electrician did in 2015, isn't it? Was my panel configuration not common in the US? In the Philippines. It's widespread.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Wed Mar 13, 2019 12:47 pm 
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Ommi wrote:
Well. 208v arc flash is so rare even for IEEE (they had only 1 case) so hope they can take my case as example of low voltage 208v arc flash.


The problem with your example is that based on the burn effects (arms only) it's under 1.2 cal/cm2 at the face/chest area. Again we're talking survival, not an absolute protection from injury. No arc flash standard out there guarantees that. So your case would be an example of what would be considered acceptable...the victim survived. One of the issues that we have to consider when it comes to safety standards is the Heinrich risk triangle and relative risk. The concept is that we want to treat risk equally. While we can treat likelihood very easily as a numerical exercise, we have to make a value judgement when we talk about the severity of an injury and the Heinrich risk triangle provides the basis for that judgement. So we would want say at least 10 serious injuries requiring hospitalization for every fatality, and 10 cases involving a doctor's care for every hospitalization case, and 10 first aids for every doctor's visit. That's make a value judgement. Once we have this we can very simply use the "factor of 10" to judge likelihood. In other words, we want to take steps to reduce the likelihood of a fatality to the point where a first aid case is 1000 times more likely. This is how the current probabilistic approach to risk is done. So 70E basically defines a serious injury in this context as a 2nd degree or more severe burn to the face or chest area. Naturally as mentioned earlier, fatalities are already 5-10% of those cases. So your case would be 10 times more likely than that. So we need to take steps to avoid injury in the first place (don't work energized if not necessary for instance) but once we've cleared those conditions then when it comes to the PPE evaluation, if the calculated incident energy does not exceed 1.2 cal/cm2 at the face/chest area (no second degree or more severe burns) which the injury case you have described does not exceed this threshold, PPE would not be required.

Quote:
After looking at more pictures. I think it is 3 phase arc flash that involves all 3 phases (the other 2 just minor):

This was taken a day after the incident in 2015 inside my car:

Image


This is typical for 3 phase arc flash. The A and C phases are quite far distant from each other. So quite often when the A-B arc or the B-C arc extinguishes, you get an arc from A to the enclosure and then from the enclosure to the C phase. This is one of those unusual things that researchers have noticed from high speed video of testing arc flash. It happens even with ungrounded systems and it is simply a consequence of the fact that a double line to ground arcing fault may be the lowest resistance path compared to line to line from the two outside phases. Knowing that you have all 3 phases melted plus two spots on the grounded surface kind of throws out the single phase theories...or at least we can't tell enough to see what is going on.

Quote:
How does one contact the IEEE committee? Do they accept 208v arc flash cases in other countries (especially one where the USA has duplicate power system they created nearly 50 years ago)? Who is IEEE committee here. Let it become an example of a 3-phase open delta arc flash case involving 208v (in which they had only one case so far only (?)).


Slow down there. First off you're in the right spot. The chairman of the IEEE 1584 draft committee is none other than Jim Phillips, the guy that started this forum. I'm reasonably certain that Jim reads almost every post, if not every one. So you've already communicated it to the committee chair. There isn't any higher position you could contact.

Second bear in mind what I'm saying. The original 2002 test data set was about 300 cases of laboratory created tests. At that time PG&E did a preliminary experiment that showed that serious arc flash below 240 VAC was essentially impossible. Subsequently we have found that the experimental procedure developed originally by IEEE had some issues. As a result the wire "fuse" size was reduced, the minimum arc gaps tested were reduced, and new models including box-barrier were introduced. The results were used in the new test data that has now expanded to thousands of tests that were used to develop the new 2018 edition of IEEE 1584. And my previous paper on low voltage arcs was written a couple years ago, BEFORE IEEE 1584-2018 was released. As I mentioned earlier they have actually found conditions under laboratory tests where they have exceeded 1.2 cal/cm2 for 208 VAC. The "barrier" paper I referenced talks about the "single case" (as in single laboratory test) and for the first time showed several laboratory tests that easily exceeded the IEEE 1584-2002 empirical equation and test cases as it existed at that (2002) time. This is also what drove the "<240 VAC, <125 kVA transformer" rule in the 2002 edition down to only 2 kA maximum fault current that is in the 2018 edition. Finally there is at least one US OSHA documented case in 2009 in which a fatal injury occurred from a 208 or 240 V arc flash in Georgia. So cases far worse than your example have already been documented. At least your electrician is still alive.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Wed Mar 13, 2019 3:56 pm 

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PaulEngr wrote:
Ommi wrote:
Well. 208v arc flash is so rare even for IEEE (they had only 1 case) so hope they can take my case as example of low voltage 208v arc flash.


The problem with your example is that based on the burn effects (arms only) it's under 1.2 cal/cm2 at the face/chest area. Again we're talking survival, not an absolute protection from injury. No arc flash standard out there guarantees that. So your case would be an example of what would be considered acceptable...the victim survived. One of the issues that we have to consider when it comes to safety standards is the Heinrich risk triangle and relative risk. The concept is that we want to treat risk equally. While we can treat likelihood very easily as a numerical exercise, we have to make a value judgement when we talk about the severity of an injury and the Heinrich risk triangle provides the basis for that judgement. So we would want say at least 10 serious injuries requiring hospitalization for every fatality, and 10 cases involving a doctor's care for every hospitalization case, and 10 first aids for every doctor's visit. That's make a value judgement. Once we have this we can very simply use the "factor of 10" to judge likelihood. In other words, we want to take steps to reduce the likelihood of a fatality to the point where a first aid case is 1000 times more likely. This is how the current probabilistic approach to risk is done. So 70E basically defines a serious injury in this context as a 2nd degree or more severe burn to the face or chest area. Naturally as mentioned earlier, fatalities are already 5-10% of those cases. So your case would be 10 times more likely than that. So we need to take steps to avoid injury in the first place (don't work energized if not necessary for instance) but once we've cleared those conditions then when it comes to the PPE evaluation, if the calculated incident energy does not exceed 1.2 cal/cm2 at the face/chest area (no second degree or more severe burns) which the injury case you have described does not exceed this threshold, PPE would not be required.

Quote:
After looking at more pictures. I think it is 3 phase arc flash that involves all 3 phases (the other 2 just minor):

This was taken a day after the incident in 2015 inside my car:

Image


This is typical for 3 phase arc flash. The A and C phases are quite far distant from each other. So quite often when the A-B arc or the B-C arc extinguishes, you get an arc from A to the enclosure and then from the enclosure to the C phase. This is one of those unusual things that researchers have noticed from high speed video of testing arc flash. It happens even with ungrounded systems and it is simply a consequence of the fact that a double line to ground arcing fault may be the lowest resistance path compared to line to line from the two outside phases. Knowing that you have all 3 phases melted plus two spots on the grounded surface kind of throws out the single phase theories...or at least we can't tell enough to see what is going on.

Quote:
How does one contact the IEEE committee? Do they accept 208v arc flash cases in other countries (especially one where the USA has duplicate power system they created nearly 50 years ago)? Who is IEEE committee here. Let it become an example of a 3-phase open delta arc flash case involving 208v (in which they had only one case so far only (?)).


Slow down there. First off you're in the right spot. The chairman of the IEEE 1584 draft committee is none other than Jim Phillips, the guy that started this forum. I'm reasonably certain that Jim reads almost every post, if not every one. So you've already communicated it to the committee chair. There isn't any higher position you could contact.

Second bear in mind what I'm saying. The original 2002 test data set was about 300 cases of laboratory created tests. At that time PG&E did a preliminary experiment that showed that serious arc flash below 240 VAC was essentially impossible. Subsequently we have found that the experimental procedure developed originally by IEEE had some issues. As a result the wire "fuse" size was reduced, the minimum arc gaps tested were reduced, and new models including box-barrier were introduced. The results were used in the new test data that has now expanded to thousands of tests that were used to develop the new 2018 edition of IEEE 1584. And my previous paper on low voltage arcs was written a couple years ago, BEFORE IEEE 1584-2018 was released. As I mentioned earlier they have actually found conditions under laboratory tests where they have exceeded 1.2 cal/cm2 for 208 VAC. The "barrier" paper I referenced talks about the "single case" (as in single laboratory test) and for the first time showed several laboratory tests that easily exceeded the IEEE 1584-2002 empirical equation and test cases as it existed at that (2002) time. This is also what drove the "<240 VAC, <125 kVA transformer" rule in the 2002 edition down to only 2 kA maximum fault current that is in the 2018 edition. Finally there is at least one US OSHA documented case in 2009 in which a fatal injury occurred from a 208 or 240 V arc flash in Georgia. So cases far worse than your example have already been documented. At least your electrician is still alive.



You mean many cases like mine with 208v to neutral arc flashed occurred but the incident energy was only less than 1.2cal/cm2 at the chest/face area yet 19.2 cal/cm2 at at 1/4 the distance (I know it quadruples every half distance) injuring just the arm and fingers causing 2nd degree burn, but IEEE ignored this because they just want to focus at the chest face area? Or are cases like it where arm got burn from 208v to neutral arc flash is not common? If it is not common, then my example is proof the barrier theory is correct. If it is common, then it makes sense and everything tallies (with no illogic that bewilders me) and I can move on already. Please let me know the case. Thank you.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Thu Mar 14, 2019 12:45 pm 
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Quote:
208v arc flash is said to be rare in the US. How come. In office or commercial. How often do you use 208v 3 phase. Does the open delta configuration produce more short circuit current than integrated 3 phase transformers? What kind of panels were the breakers installed. Maybe no one was stupid to land any live wire to the breaker input terminal like what my electrician did in 2015, isn't it? Was my panel configuration not common in the US? In the Philippines. It's widespread.


Open delta is a higher impedance which results in lower short circuit current. I'd say 99% of the arc flash incidents that OSHA has documented at least though were 480 V and above. ESFI has some pretty good documentation on it. It's pretty even across the voltages with no one voltage prominent over any other except that 240 VAC and below is much less prevalent. Not that there isn't a lot of it but that it takes the right circumstances.

Second missed it but your comment about 3 bus bars in an open box not being representative...well at the time they were looking for repeatable tests that could be used for laboratory purposes so an artificial scenario was a necessity. And at the time the impact of things like horizontal barriers as well as phase barriers and many similar items was essentially unknown. The model they chose was substantial enough that it would survive more than a single test so it worked out pretty good and got a lot of good data in a short period of time. High current testing lab time is definitely not cheap and the entire effort for the most part came from voluntary donations of time and money, and still does. The barrier paper you have the reference for is now pretty old but prior to that we didn't even have a starting point...no IEEE 1584 empirical model so we didn't even know that it was worse than the "normal" test case. So it was very revolutionary at the time. But if you read the paper the conclusion is also that it's obvious that it's a problem but not enough data to know what to do about it.

Quote:
You mean many cases like mine with 208v to neutral arc flashed occurred but the incident energy was only less than 1.2cal/cm2 at the chest/face area yet 19.2 cal/cm2 at at 1/4 the distance (I know it quadruples every half distance) injuring just the arm and fingers causing 2nd degree burn, but IEEE ignored this because they just want to focus at the chest face area? Or are cases like it where arm got burn from 208v to neutral arc flash is not common? If it is not common, then my example is proof the barrier theory is correct. If it is common, then it makes sense and everything tallies (with no illogic that bewilders me) and I can move on already. Please let me know the case. Thank you.


Need to go back and look at the theories behind this. It's not that it's being ignored but let's step back for a moment and look at this. What do you propose we do about it? This is a Xeno's bridge problem...at least in theory arc flash gets exponentially worse as the distance decreases. We can't build protection against that short of avoiding the problem in the first place. At some point it's not an arc flash anymore...it's outright shock. You can't prevent ALL injuries except if you move the people far enough away to be safe or work in such a way that you don't cause an arcing fault in the first place. Expecting PPE as a solution is completely unrealistic at this point. Arcs can burn through solid metal with enough time. That's what arc gouging is all about. So there's no way to stop it. So you need to recognize ways to prevent the hazard in the first place. Failing that ways to minimize injury to something less than death or serious injury. That's the point of the standards.


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 Post subject: Re: Quantity of carbonized particles before Arc Flash Initia
PostPosted: Thu Mar 14, 2019 1:40 pm 
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There are two fallacies out there when it comes to hazards in general and electrical hazards in particular.

Fallacy #1 is let's just call it the Eurofallacy. This is the belief that we can simply design away hazards. That all problems with shock and arc flash are simply because of poor equipment design, that it's a manufacturer problem. In the mean time we'll just stick our heads in the sand and ignore work practices and PPE solutions.

Fallacy #2 is prevalent with a lot of "the most safe organizations in the world". These are primarily chemical and other large industries that persist in the idea that they can bureaucratize their way out of any injury. That if we just have enough paperwork and procedures, injuries will never happen. Or better yet we can simply blame the employee for not properly filling out all 25 pages of paperwork and procedures before they begin a job. That they didn't take the paperwork seriously. This is the group that came up with the JHA/JSA paperwork that 70E added to every electrical task thinking that this will make the problem go away. Well I can tell you for sure that there is ZERO documented evidence that this does anything at all. If anything there is strong empirical evidence that it does just the opposite, reducing rather than improving safety. Because as we add more and more layers of bureaucracy that have absolutely nothing to do with positive actions taken to actually prevent injuries from occurring, the tendency is towards ignoring them, "pencil whipping", and the like. And once you condone/validate/approve of employees doing this tacitly or explicitly then you give them permission to ignore still yet other safety rules, ones that really do matter. So we end up with decreasing safety rather than improving it.

Fallacy #3 let's call it the American fallacy is thinking that there should be a product out there that provides a quick fix. Just wear these special gloves or that special hood and all your problems go away. That PPE is the quickest, easiest, and best solution to all safety problems. There is a reason why PPE is the last ditch effort and the lowest priority on the list of priorities whether you subscribe to ANSI Z10 ("hierarchy of controls") or to the European version known as ALARP or ALARA. The result is the same. PPE fails. Employees can fail to wear it properly, cut the sleeves out in hot climates, wear it out, get it soaked in oil or grease, get holes torn in it, you name it. And that's even before we get into the fact that it can be defective on it's own. PPE is just about the least reliable of all the things I've stated in this post. So the key is not to rely on it as the first and foremost solution. This is over and above the fact that you cannot stop all arc flash. There comes a point where the amount of heat exceeds the technology to contain it. That's why plasma torches, arc gouging, and electron discharge machining (EDM) function.

Taken together yes there is equipment that can help. For instance there is arc resistant switchgear. This isn't available for all situations and all cases. It does great at protecting production people when the doors are closed and latched. Once you open the doors for maintenance purposes, all the fancy arc resistant features disappear and it does nothing for the maintenance worker. Knowing that 70E for instance has stated that normal operation is safe, arc resistant switchgear is really a solution looking for a problem. It is popular in Europe and Australia for instance but knowing what it does and doesn't do, it's kind of a huge expense for nothing. You can also have remote operated switches and breakers as a more obvious and good solution BUT those only work as long as they are working. Once the coil burns up for instance, someone has to fix it. So the fancy remote control no longer works at all. Similarly for switchgear there are retrofit remote motor operators. They fail too. Sometimes they even damage the equipment. So it helps sometimes but not always.

When it comes to work procedures, you can drastically cut down on the incidents if you just approach electrical work with the intent to never work energized or at least that you will only work energized when there is physically and not just conveniently no other choice. And when you do have to do it, if you use the proper PPE and look at ways to minimize exposure if at all possible in the situation. Minimizing exposure and failing that minimizing the risk all contribute to lowering the risk (severity and/or likelihood) of injury in the first place. I know this sounds too simplistic but it works.

In the U.S. the first real attempts at addressing arc flash came about in the late 1990's. It was first really introduced to "the world" in 2002 in the National Electrical Code for the first time. That's when most of us first heard about it. By 2006 OSHA issued the first fines to a large corporation. At that point anyone on the fence about whether or not to take it seriously started taking it seriously. Over the last couple decades electrical injuries have decreased by 60%. There is a clear and dramatic step change in the number of injuries even as the population in this country and the total number of workers continues to increase dramatically over the same time period. So realistically we're seeing a 60% decline in the numbers but the decline relative to the number of workers is even larger.

The last ESFI report that I saw stated (and again I disagree with the way that the guy who does the number crunching actually counts arc flash vs. shock) that the number of shock injuries is currently at around 2 workers per 100,000 per year. Arc flash is about 1 worker per 100,000 per year, and these numbers are less than half of what they were a couple decades ago. How low? So among workplace hazards if we lump electrical injuries all together given the concern over it do you think that they would be in the top 10 injury causes? No. They are 40th, and dropping. As a percentage it's under 1% of all injuries, far, far behind slips, trips, and falls for instance. So without even addressing whether or not <250 VAC arc flash is a very rare event (which it is) arc flash is a very rare event.

Personally, I think IEEE and NFPA and ASTM has done a pretty good job with this. If I could do better, I would submit things to make that happen. I would suggest though that you need to offer solutions rather than throw up roadblocks. One thing to keep in mind though particularly with IEEE is that it only took 16 years to update from the last version. It is a VERY slow process. The IEEE standards committees are full of both academic purists and very pragmatic people. The purists would have us study the problem for another 200 years until we have perfected the science to the 10th decimal. The pragmatists would have us do something very practical but so oversimplified that it does not address the problem. And both groups need to agree to the point where we can achieve a consensus opinion and thus move on to publishing a standard. That's why it took 16 years. NFPA procedures on the other hand have a much simpler process that does not quite build consensus in the same way but virtually guarantees that we will get something out of the process, even if it's not something everyone can agree on. So we get an update from NFPA every 3 years. Oh and by the way, the IEEE and NFPA organizations are rivals. They compete with and don't really like each other.


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