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 Post subject: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Wed Jun 18, 2014 5:43 pm 
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At work we have no real rhyme or reason with our arc flash policy. We were issued Category 1 shirt and pants while not being issued any other safety equipment. The work is on HVAC equipment ranging from 40 hp drives to window shaker air conditioners. While I can get across the idea of a lot of current and voltage making a big bang I am at a loss how to get across the magnitude of an arc flash event from a small panel feeding a wall outlet in an office. Does anyone have a relatively simple way of explaining the amount of danger in terms that a non-technical person could understand?


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 Post subject: Re: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Thu Jun 19, 2014 8:00 am 
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Quote:
At work we have no real rhyme or reason with our arc flash policy. We were issued Category 1 shirt and pants while not being issued any other safety equipment.


A couple of thoughts on that statement:
1. Sounds like a salesman got in and convinced management that some FR clothing was needed and no one really investigated the type of work being done.
2. No other safety equipment??? No safety glasses? No rubber gloves? No insulated tools?

Your subject title states 15A, 120V but no way will a 40hp motor run on that. So I guess need more information about what are the voltage levels you working on. The basis of calculating arc flash hazards is IEEE 1584 which is only for 3 phase systems up to 15kV. Single phase is usually considered to be a low arc flash hazard.

It also seems like you are a service technician that goes to customer sites to troubleshoot/repair equipment. As such the employer (site owner where you are working) needs to provide you with the hazards at his facility including arc flash hazards (OSHA). That way you can wear the appropriate PPE for the hazards at the site.


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 Post subject: Re: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Thu Jun 19, 2014 7:26 pm 
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We are a campus of about 20 buildings ranging from 100 years old to just a couple years old. Most of the electrical is up to date so not much worry about old wiring or faulty equipment. Well that is not including a speed drive project where we put in about 100 of them from one manufacturer and about 1/3 have already failed, replacing them with another manufacturers product that we had a good track record with. We do have a separate electrical shop and they have all the safety gear, ours takes care of the HVAC and some building controls. Safety glasses, yes but not specifically for electrical hazards, no rubber gloves, tools insulated in that side cutters, needle nose pliers, and screwdrivers all have some sort of plastic coating. I would not trust my life to them.

Exhaust fans up to 1/2 hp could be on 120V otherwise most motors on 600V. In Canada not in the U.S. so no OSHA. Suppose to have a copy of CSA Z462 around somewhere but when I raise questions on our policies I get stonewalled. They know that they just pulled this out of somebody's hat without spending any time looking into what is necessary. Rumor has it that they will hire an engineer to tell us what we need but a year and a half has gone by so far, still looking for funding I guess.

Back to the 120V. The reason I am asking is I know their is practically no arc flash danger but when dealing with HR types if you get too technical their eyes roll back and they just say nothing trumps safety and that is that. We have a position dealing with fire alarm systems that we would like to fill with a person that has medical issues. All the equipment is 24V other than the odd relay that switches a relay with 120V fed by a 15A breaker. They can not seem to understand he does not need to be wearing Category 1 shirt and pants 8 hours a day especially when he would rarely be in a panel with the offending relay.


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 Post subject: Re: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Sat Jun 28, 2014 6:10 am 
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Would suggest that you and perhaps some HR folks get training. ESPS is a training company in Canada that offers online training (no need to pay someone to come out) for aroung $60 per person last I knew, or about the price of one pair of FR pants. The training is good enough that a major potash mine in Saskatchewan uses them.

Z462 is identical to 70E verbiage. There formatting is different to meet CSA format rules instead of NFPA and there are some different annexes. But the meat is word for word identical. I realize that even though 462 sets a 50 volt rule, some provincial regulations do strange things with the rule without any technical reason (NB, ON).

24 V systems are relatively safe for 2 reasons. First the arc will not sustain itself. Second I know of no recorded cases anywhere of a fatality.

120 V is another matter. It is certainly a shock hazard. There was an accident in Georgia in 2009 in a 240/120 temporary construction/ lighting panel that resulted in one hospitalization and one fatality. So you can't say the hazard is categorically low. IEEE 1584 suggests that if the transformer is under 125 kva and the circuit is 208 v or less, that the hazard is less than 1.2 cal. However more recent research has shown that the limit should be dropped to around 45 kVA or less. Also based on testing in the utility industry IEEE C2 has set a standard of 4 cal for 250 V or less panels. So without doing any kind of engineering analysis at all, it seems like the 4 cal stuff you were issued is very reasonable for 120 V. Keep in mind...the testing and calculations for 120 V systems are guesses. It is very difficult to get repeatable results because arc stability is borderline...it tends to self extinguish.

The rule for 1.2 cal is nonmeltable clothing which usually means cotton, wool, silk, or other natural fibers. Synthetics like almost all the winter linings tend to melt and create more injuries. That being said, even up to 10-12 cal shirts and pants have been proven to be thermally the same or less insulating than standard industrial cotton 12 oz shirts and pants. There is no heat exhaustion hazard here. It feels different no doubt, and it will not be "work dry" unless you buy the super expensive drifire or dragonwear shirts. But its no worse. Some companies are mandating 4 cal uniforms just to eliminate any arguments with guys about the clothes they bring in from home.

As to the shock hazard that you are touching on, Z462 guidance is basically not to touch it or work deenergized. I have no problems with my guys using a meter with probes that have the tip covers so they can't drop one and get an arc and also with the flared part that prevents your hand from slipping past the insulated handle. This is acceptable under IEEE standards for energized work methods for "no contact" but would not be necessarily acceptable above 250 V. I do not allow live work at all on 250 Volt or less beyond diagnostics except some HVAC and some pole lights the only way to deenergize is to pull fuses. Also landing circuits in an energized lighting panel is sometimes necessary and can be done safely and is less of a hazard but there are dozens of cases in OSHA accident investigations of guys trying to drill and tap live lighting panel bus work with predictable results. And if you are near 600 volt equipment that is exposed, you use the 600 volt rules for shock protection or cover it. Rubber voltage rated blankets and clothes pins (lineman "cover up") is cheap and easily available, and you can cut it to fit anything. In Canada as in the US authorities take a dim view on the idea of working live vs. deenerigzing.

It sounds though to me that you have a lot of questions, concerns, and fears of the unknown. The above training is pretty good and Terry does a decent job of staying away from the scare tactic stuff that some trainers use. The fact that as an HVAC guy you are genuinely concerned for safety and doing things right is very refreshing. The above potash mines truly struggle with outside service contractors that don't have the same view. Even though I'm an American I've sat across the table from SK provincial labor authorities and even Sask Power struggling with the same issue. However based on your description even though you'd like someone to side with you and clearly your HR folks are having some concerns about what they no nothing about either, I can also say that they are not too far off track. If you go for the 4 cal requirement, the rest of the required PPE is leather boots, all leather or voltage rated or arc rated gloves, class E hard hat, safety glasses, and ear plugs.. It says leather boots and this is an obvious issue around water or in the winter. We've tested some boots (not cheap). I don't have any good answers other than to say that the standard is based on keeping you alive, not to totally prevent injury and definitely is not intended to keep from major injuries to your limbs. I know the glove thing can be a struggle. While offering no electrical properties, TIG welding gloves are fire retardant and just about the thinnest all leather glove on the market. Just be sure to get the kind with a bit of a cuff so that it does not leave your wrist exposed. Special insulated tools (pliers, wire cutters, wrenches, screwdrivers) are available. But as I said, I am not in favor of working live. Z462 is also very restrictive about this. You should only be working live if you are doing diagnostics where it is impossible not to work live (can't test for voltage if power is off), under 50 volts (mjnimal hazard), or when your company (should be a safety person or other manager/supervisor involved that could go to jail if an accident were to happen and OH&S made criminal charges) determines that there is a greater hazard to deenergizing than not. For HVAC this would have to be a pretty extraordinary case. Final case is when working deenerigzed is not possible, but I have never found one. OSHA says that loss of production, inconvenience, etc. does not count. Hospitals used to do some vague hand waving with regards to operating rooms and people on life support but after an accident that killed one and sent 4 others to a burn unit, many have been more accepting of deenergizing.


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 Post subject: Re: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Thu Oct 02, 2014 12:46 pm 
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Hi Paul,
Thanks for mentioning the IEEE C2 requirements for 120V, I assume that this is only in the 2012 version of this standard and not earlier versions. Could you confirm?

cm


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 Post subject: Re: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Mon Oct 06, 2014 5:37 am 
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Hi,
I was able to find the reference to the language in Section 41 of the 2012 NESC regarding the General requirements for arc flash hazard assessments.

Thanks again for mentioning them, since we do work for both utilities and industry, it is always helpful to know if there is another set of guidelines in existence.

CM


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 Post subject: Re: Almost not worth mentioning, 120V 15A circuit...
PostPosted: Tue Oct 07, 2014 8:07 am 
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I can confirm that the "low voltage" tables were added to IEEE C2 (NESC) in 2012 edition only, not in the previous edition.

The previous edition had a cutoff of 2.0 cal/cm^2 for arc flash hazards. This is also used in the new OSHA 1910.269 rules. It is at odds with the 70E 1.2 cal/cm^2 minimum.

Also in the verbiage (over 1000 pages) leading up to the revised 1910.269 rules there is a lot of discussion about a "4 cal/cm^2" minimum. OSHA takes the stance that if everything is under 2.0 cal/cm^2, then an FR clothing requirement can be dropped. Otherwise, they adopt a 4 cal minimum. When several queries were asked about why this would be required for <1.2 cal/cm^2 work, the response was that the FR clothing does more than just protect against thermal burns. It also protects against spalshes from molten metal and similar things that may cause injury from equipment further away, even if arc flash is not directly involved.

Some recent papers at Battcon show a maximum measured incident energy of right at 1.2 cal/cm^2 when corrected for working distance and maximum measured arcing time for a 130 VDC arc with an available short circuit current of 20 kA. This is not AC. I can't really find much over a cycle or two for 120 VAC, and even EPRI data at 208 VAC (3 phase) is pretty low as well. IEEE 1584 was only able to sustain an arc for a single test case. IEEE 1584 gives a suggestion (not a "rule") of <1.2 cal/cm^2 for a single transformer feed of 125 kVA or less at 208 VAC or less. Recent test work suggests this should be lowered to around 45 kVA and more specifically it corresponds to a fault current of around 4.5 kA with a reasonable X/R ratio. With most 120/240 VAC circuits having almost 1.0 X/R this almost makes it impossible to sustain an arc based on the same test data and is mostly the case for lighting panels.

Then we get into the issue of "lab" vs. "real world" data. I can confirm (but can't reveal sources) that it is even possible to create an arc at least at around 240 VAC, 3 phase, with high X/R, high available fault current, and very short gaps that exceeds even 4 cal/cm^2. However we then get into the argument about whether or not this represents a laboratory case or a "real world" case. At low voltages even the "fuse" wire becomes an issue because the wire has to melt/vaporize and have a low enough resistance to actually create enough heat and plasma to form a sustainable arc. This may in fact be further indirect evidence that low voltage arc flash is pretty unlikely in the first place. Some of EPRI's testing is moving towards trying to simulate "real world" scenarios by doing things like jamming a screwdriver into triplex conductors or clamping a pair of vice grips onto a bus rather than using the standard "fuse wire" which is a #10 wire shorted across all 3 buses.


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