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 Post subject: To label or not to label. That is the question.
PostPosted: Tue Oct 14, 2008 12:32 pm 

Joined: Tue Mar 25, 2008 1:00 pm
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Alright, so NFPA 70E: 2009 states an arc flash hazard analysis is not required is circuit is <240V, supplied by on transformer, and transformer is rated less than 125kVA. NEC 2008 states equipment that is likely to require energized work shall be labeled.

So what if the panel nor requiring an analysis per NFPA 70E will require energized work? And if you did put a label on it, NFPA 70E requires that label to state the incident energy or PPE required. What then?


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PostPosted: Tue Oct 14, 2008 6:41 pm 
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Are you implying that there are flaws in the code?
What I do is affix a label anyway and list the minimum ppe we allow for any live work and the IE associated with it. So for us, we would put a label on it, Level 1 PPE, 4.0 cal/cm2 and then list the phase to phase voltage. My interpretation is that the exemption does not require an analysis, ie, calculating the bolted fault current, the arcing current, looking up the breaker clearing time, etc, etc. The exemption from the analysis does not mean you are exempt from labeling. If you compared this to the 70E PPE task matrix table you will see PPE is required for panelboards under 240v for voltage checking, inserting breakers, etc. Sometimes that PPE is Level 0 other times its 1. I would speculate you could make it -1 if you desire since it is exempt from analysis. 2009 is when we have to list the PPE on the label. But since 2009 also permits use of the Table, I suppose the PPE Level will read " PPE as per NFPA 70E (x)(x) Table. (sorry, don't remember the table ID number).


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PostPosted: Wed Oct 15, 2008 7:27 am 

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Having thought about this some more, I like your idea. On another matter though, does the difference in results between IEEE1584 and NFPA70E worry anyone? I have a panel with an AFB of 11 inches in NFPA70E result in an AFB of 111" based on IEEE1584 equations. Shouldn't we have some sort of consensus?

Which of the two sets of equations are most people using for their analyses?


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PostPosted: Wed Oct 15, 2008 9:55 am 
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The NFPA70E PPE matrix is a poorly thought out and very dangerous "attempt" to simplify the way to determine general ppe levels without conducting a accurate short circuit study and IEEE 1584-2002 arc flash evaluation. I don't use or agree with the NFPA PPE matrix for a number of reasons. First and foremost, it allows exposing workers to dangerous if not fatal arc blast situations by specifying the wrong ppe. As example: I recently did a large facility study for a customer that has 10 substations, all with 26.7kV pri/480 V sec - a mixture of 1500 & 2500 kva AO transformers, feeding 480 volt LVPB switchgear feeding MCC's. One of the transformers in the survey, a 1500 kva, 5.55 %Z, delta - delta ungrounded type with 480 volt secondary feeders consisting of 5 each, 3C/500 mcm cables, over head cable tray - 100 foot runs to the switchgear main bus. No PD at the xfmr secondary terminals. Ok... The NEC states the 25 foot secondary tap protection rule doesn't apply to delta - delta xfmrs. So technically the installation met NEC standards. The NFPA 70E PPE matrix for switchgear and panelboards lists, "Working on energized parts including voltage testing >240 volt but < 600 volts is a classified as Cat 2*" (Anyone pick up on the what's wrong yet?). Joe Middle Manager crows... "See good ol' NFPA has done all the work. I don't need to spend money for a stink'in professional study. Slap on a few generic stickers and I can save the company a bundle. That will look really good on my next review." Although in reality the short circuit study show a much different result for this substation xfmr switchgear. The arc flash incident energy calculated out to 54.5 cal/cm2, 11 foot FPB and exceeded max PPE levels. The only protection is the xfmr's 26.7kV primary side, consisting of medium speed 40E fuses. The fuse melting TCC at 85% Ia is a real flame thrower. Sooo.... an electrician voltage testing wearing only 2* ppe as listed by NFPA would have been critically burned if not killed if an arc flash event occurred. Incident energy blasts above 40 cal/cm2 is not considered survivable. Now lets talk law suits, lawyers, OSHA fines and workmens comp claims that can cost a company millions. Now Mr. Money saving Joe Middle Manager... NFPA PPE matrix in hand... is sitting on the witness stand being chopped to pieces by the attorney of the dead electrician's family. Lawyers live for this stuff! This is why smart companies pay electrical professionals to do detailed analysis. It's not just crunching numbers to come up with a cal/cm number, any half-wit bozzo can buy software to do that. It's about having the electrical experience, training and knowledge to interpret the data and do a total electrical system evaluation. In the case I listed above, the electrical engineer of this company never picked up on the NEC delta - delta tap rule vs. the arc fault incident energy levels. Not because he isn't intelligent... but didn't have the experience to evaluate the data and correlate the two standards. This isn't the first time I've run across this type of situation. Companies looking to cut $$ corners by doing arc fault on the cheap by only relying on a generalized NFPA PPE table is dangerous and IMHO fool hardy. Would you be comfortable with your doctor using a generalized "fits all" chart to diagnose if you needed major surgery?? This is a typical situation of NFPA trying to over simplify a complex problem. Sorry NFPA70E it isn't working very well. Sorry for getting long winded but the PPE matrix should be removed for NFPA70E. I'm sure I will get flack about this!


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PostPosted: Wed Oct 15, 2008 5:27 pm 
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Not from me, all valid points.


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PostPosted: Wed Oct 15, 2008 6:16 pm 
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GEH,

What you should have done was explain the footnotes in the table and educate the person that you can only use the Table if it is within the dynamics from which the Table was developed, ie, in this case 25KAIC and 2 cycle. Transformers that large are going to have more than 25K fault current and since they only have primary protection on the transformer you know its more than 2 cycles.

I would have to disagree with you about the value of the Table. Just because NFPA didn't implement it correctly doesn't mean it was a bad idea. Square D is quoting prices of $50 to $70 thousand to do analysis of a typical chem plant. Maybe a 100,000sq ft single building manufacturing site would cost about $13,000. Is it really reasonable to expect this small of a manufacturer to spend this amount of money, plus buy all the arc flash PPE. The Table helps to minimize this financial burden. NFPA just did a poor job in implementation. They were so much in a rush to collect their sale price, they didn't even bother to correct the footnotes of the Table, they did that on the next page with a TIA. Then they don't even layout the corrections in a way that is easy to understand, they list the notes 1,2,3,4 with reference to footnotes 1,2,4,5. How many people miss that one.

NFPA needed to realize that the TABLE would be the principle implementation tool for small business. Their original fault current values were okay but there clearing times were way to fast to simulate typical installs. They should have went for 10 cycles at least. Then their PPE results are about one level higher than what you would expect if you used the IEEE formulas at that Ibf and t. I guess there built in safety margin. They should have kept the Ibf where it was and then calculated IE at 10 cycles and then posted that ppe level without any safety margin. Further the guide needed to provide more documentation and guidance in the Table use.

The 2009 is just as bad. I have no idea why the felt they needed to change the limits for the 4ft default AFB. One thing NFPA needs to learn is to not rush to publish until they have their facts, and once published don't change unless their is a gross misapplication. All they do is confuse more people by changing this tolerances constantly. Plus, how could NFPA make a 100% error when they published 300KACycles and now need to revise it to 166KAcycles. If I did that at my job my boss would have me cleaning toilets - if I was lucky enough to keep my job.

Regarding AFB discrepancies, I have seen doubles and halves from NFPA versus IEEE, but never 10 times. Something may be wrong there and I would recheck the math. Post the values and we can all run them. They are different and most people will use the IEEE values if they are performing and IEEE based analysis, and the Ralph LEE or Default of 4ft if they are using the Table.

Another point I would make similar to my recommendation for a universal minimum of PPE and IE on the labels is - try to create a universal AFB for under 600V and another for over 601V. In my site I performed the calcs and built my spreadsheet, for under 600V the largest AFB was 50", so now all my labels say 60" on all labels under 600V and over 601 I have a universal 15ft. Now at my safety meetings when I ask the electricians if they know the proper AFB they all say in unison, 5feet and 15feet. The best program is one that is easy to understand, and easy to implement.

Remember the labels are minimums, they are NOT to show how scientific we can be or how much math we can manipulate. The label does NOT have portray the exact values from the calculations, the values can be that or higher to maintain a common standard.


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PostPosted: Wed Oct 15, 2008 6:59 pm 
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Haze,

Tables are good when when they are statically proven based on sound data... not bottom loaded table with fine print foot notes. I agree in most cases the 4 foot rule for the typical 300 kva, less than 25KAIC system, mom & pop machine shops works but it's the "one offs" that get ya every time. Dealing with 3000, 4000 kva and larger units is another ball game. As in the case study I listed in the last posting it was one odd ball delta-delta xfmr that was the "got ya". The rest are delta-wye, high Z grounded center tap systems. Mostly cat 1 stuff. Yes, detailed studies can be costly but law suits cost millions to litigate. I do my surveys from the "witness stand back" theory. You have to prove what you are saying with facts... not based on a generalized table or assumptions. The company with the no PD on the delta-delta xfmr secondary corrected the situation by installing 2500 amp fuses at the xfmr secondary terminals and replacing the medium speed 40E primary fuses with high speed fuses. Total cost: $15,000 parts and labor. This also protects a $95,000 transformer from damage along with all the assoicated lost production down time.


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PostPosted: Mon Nov 17, 2008 10:11 am 
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Even within the allowances of the footnotes to the tables, we have calculated exposure that exceeds the prescriptive tables (and also many that are lesser). For the small transformers, we adopted a minimum RC of "1", but because we found surprises we did perform calculations to verify that was conservative. We then put generic labels on all the panels that were below risk category 1.

Regarding the cost of doing these studies, our greatest time has been spent gathering system information. That can take seemingly forever and then field checking what was provided indicated many corrections. It is time consuming expensive work. But what we found was a 50year legacy of inconsistent circuit breaker settings and random sizing criteria. It seemed like every engineer had his own philosophy and there was no consistency. Simply tabulating the settings for 30 substations made many errors apparent and I hope the customer recovers much of our engineering fee in provided greater reliability. Design guidelines were developed from what started as an arc flash analysis. If these are continuous process plants, unscheduled shutdowns might be expensive. I know of a momentary outage that cost $850K, that makes a study seem economical. The alternative is that these systems may be worked cold.


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 Post subject: Re: To label or not to label. That is the question.
PostPosted: Sun Dec 21, 2014 9:40 pm 

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If you compared this to the 70E PPE task matrix table you will see PPE is required for panelboards under 240v for voltage checking, inserting breakers, etc. Sometimes that PPE is Level 0 other times its 1. I would speculate you could make it -1 if you desire since it is exempt from analysis. 2009 is when we have to list the PPE on the label.

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 Post subject: Re: To label or not to label. That is the question.
PostPosted: Wed Jan 21, 2015 12:13 pm 
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deprico wrote:
Alright, so NFPA 70E: 2009 states an arc flash hazard analysis is not required is circuit is <240V, supplied by on transformer, and transformer is rated less than 125kVA. NEC 2008 states equipment that is likely to require energized work shall be labeled.

So what if the panel nor requiring an analysis per NFPA 70E will require energized work? And if you did put a label on it, NFPA 70E requires that label to state the incident energy or PPE required. What then?


First off it is saying that it doesn't require analysis because it is estimated that the incident energy is less than 1.2 cal/cm^2. So we can certainly label it. There are debates going on as to whether the cutoff is the right number or not but then again, there are also debates as to whether the calculated incident energy even for the "normal" cases is correct.

To meet NEC, it has to have a "label" warning of arc flash. It can be a simple "Warning! Arc flash hazard may be present". This is of course useless but complies with the mandatory Code. It violates the voluntary Code (70E) but then again, 70E gives very little guidance for the low hazard cases. Then there is the practical issue. Most operations are now requiring non-melting clothing as standard workwear for electricians. Some have gone further either due to overlapping requirements (plants with molten metal or petrochemical typically require FR clothing) have a higher standard. Thus most electricians more or less "automatically" meet either 1.2 or 4 cal/cm^2 as the required standard workwear. And although this is a Code violation rather than spend the money and time marking panels with a warning that is basically meaningless because no additional precautions need to be taken, many are also stating in plant rules that unmarked panels other than new construction are automatically either 1.2 or less or 4 or less cal/cm^2. And the only practical time that NEC is ever enforced that I've ever seen is if you have to pull permits for a construction job. Most large industrial plants don't do that for most jobs. So nobody is inspecting and they are self-policing. Plus, 70E is voluntary, and the current label requirement has not exactly been universally applauded.


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