Is it ever ok to work on exposed live parts per 70E?

[hillbilly1]

Again, a wrong old teaching based on scare tactics.

The 70e instructor said that, anything needed above a 40 cal suit was worthless because the compression blast would kill you by crushing, not the burn.

 

[jim dungar]

The 70e instructor said that, anything needed above a 40 cal suit was worthless because the compression blast would kill you by crushing, not the burn.

But most 40cal events are caused by too much exposure, not too much fault current.

Your instructor was hinting at an arc blast effect which is caused likely by very high fault currents. However there is no industry standard method for calculating arc blast or its effects. Arc blast is what blows doors off of equipment. 20 years of NFPA 70 has shown there is no direct correlation between cal/cm² and explosive force.

 

[garbo]

NFPA 70E allows for energized work under three specific conditions:

De-energizing would pose a greater hazard (e.g. hospital)
De-energizing is not feasible (testing, troubleshooting)
Less than 50 V.

If the work doesn't fall into one of these 3 categories, energized work is not permitted.

The "incident energy" is a calculated at a specific "working distance". This is an assumed distance from the likely source of the arc to the worker's chest or head, whichever is closer. At 600 V and below, it's generally assumed to be 18 inches. It's always been recognized that hands and arms could be exposed to higher incident energy if closer than the assumed working distance. IIRC, 70E says that additional protective measures may be required in some situations. As others have noted, the energized work procedures in 70E are intended to prevent serious injuries and fatalities.

Years ago it took us over five years to locate the two 277 volt circuits that feed luminares in our 10,000 square foot maintenance shop so we had to work it energised while moving one of the shops double doors. One Saturday night we turned off hundreds of 277 & 480 volt circuit breakers trying to locate it. Company was too cheap to purchase a circuit tracer for the six electricians. Conduit went thru several large ceiling pull boxes where two of them had duct working blocking access. When we opened up a 600 amp 480 panel that only had three pole circuit breakers all 40 Amps & higher found some hack installed a 250 volt fuse block that had 20 amp 250 rated fuses directly tied to 600 amp panel buss with #10 guage wire. This was during the annual summer shutdown so we removed the fuse block and installed two single pole 20 amp circuit breakers. Over the years we did less & less hot work.

 

[garbo]

All the arc flash stickers we make include the safe-working distance (18") and the glove class. It's never your bare hands or a short sleeve shirt.

Just curious. When they build a building is thier a certain time line that Arc Flash labels have to be installed. My thinking is they should never pass final inspection until Arc Flash labels are installed. A year before I retired JCI (Johnson Control ) installed two 1,750 HP Chillers. Each were feed by 13,200 volt line and had a step down transformer to 4,160 volts that feed a VFD all in a maybe 18' long enclosure. I asked them several times over my last year when are they going to install Arc Flash labeling and was told they are working in it. If I was in charge no contractor would receive final payment until labels are installed. When they installed a dozen LIM panels during OR work I asked the company during a meeting about Arc Flash labels. They did not have a clue and never supplied them.

 

[hillbilly1]

Years ago it took us over five years to locate the two 277 volt circuits that feed luminares in our 10,000 square foot maintenance shop so we had to work it energised while moving one of the shops double doors. One Saturday night we turned off hundreds of 277 & 480 volt circuit breakers trying to locate it. Company was too cheap to purchase a circuit tracer for the six electricians. Conduit went thru several large ceiling pull boxes where two of them had duct working blocking access. When we opened up a 600 amp 480 panel that only had three pole circuit breakers all 40 Amps & higher found some hack installed a 250 volt fuse block that had 20 amp 250 rated fuses directly tied to 600 amp panel buss with #10 guage wire. This was during the annual summer shutdown so we removed the fuse block and installed two single pole 20 amp circuit breakers. Over the years we did less & less hot work.

When I was starting the safety program for my previous employer, I told the VP, if you want the guys to quit working it hot, you need to buy tracers. He agreed and bought $50,000 worth of tracers in the first year. The worst problem was the new hires would get the tracer “stolen” right before they quit or fired.

 

[ggunn]

Depends on if you're talking about asking real electricians...

I am, of course. I know, for example, of cases where real electricians have switched out residential service equipment without pulling the meter because the POCO would not allow them to break their seal, and scheduling a shutdown with the POCO was impaired by bureaucratic red tape..

 

[jim dungar]

Just curious. When they build a building is thier a certain time line that Arc Flash labels have to be installed. My thinking is they should never pass final inspection until Arc Flash labels are installed.

Arc flash incident energy labels are not a requirement of any enforceable code which is part of a permitting process.

Arc Flash labels are one option, and the most popular one, companies can use to satisfy OSHA and insurance worker safety requirements.

 

[don_resqcapt19]

Arc flash incident energy labels are not a requirement of any enforceable code which is part of a permitting process.

Arc Flash labels are one option, and the most popular one, companies can use to satisfy OSHA and insurance worker safety requirements.

They are somewhat enforceable with the new language in 110.16(B) in the 2023 code.(B) Service Equipment and Feeder Supplied Equipment.

In other than dwelling units, in addition to the requirements in 110.16(A), a permanent arc flash label shall be field or factory applied to service equipment and feeder supplied equipment rated 1000 amperes or more. The arc flash label shall be in accordance with applicable industry practice and include the date the label was applied. The label shall meet the requirements of 110.21(B).

Informational Note No. 1:
See ANSI Z535.4-2011 (R2017), Product Safety Signs and Labels, for guidelines for the design of safety signs and labels for application to products.

Informational Note No. 2:
See NFPA 70E-2021, Standard for Electrical Safety in the Workplace, for applicable industry practices for equipment labeling. This standard provides specific criteria for developing arc-flash labels for equipment that provides nominal system voltage, incident energy levels, arc-flash boundaries, minimum required levels of personal protective equipment, and so forth.

[/QUOTE]

While informational notes are not enforceable code, I am not aware of any other "applicable industry practice" for arc flash labeling.

 

[Joe.B]

I am, of course. I know, for example, of cases where real electricians have switched out residential service equipment without pulling the meter because the POCO would not allow them to break their seal, and scheduling a shutdown with the POCO was impaired by bureaucratic red tape..

I am not an electrician, and I know enough not to mess around. My good friend is an electrician and he likes to joke that real electricians know how to work hot. I also know a lineman and he says that if you don't have a choice, that's what you do. And if you do have a choice only an idiot would. We (building departments) get a lot of flack about red tape, but it seems like the POCO's and state agencies are way worse...

 

[don_resqcapt19]

I am not an electrician, and I know enough not to mess around. My good friend is an electrician and he likes to joke that real electricians know how to work hot. I also know a lineman and he says that if you don't have a choice, that's what you do. And if you do have a choice only an idiot would. We (building departments) get a lot of flack about red tape, but it seems like the POCO's and state agencies are way worse...

One big difference between line work and electrical work, is that in most cases the arc flash with line work goes in all directions, where as with electrical work, the enclosure directs the arc flash directly at the worker.

 

[tortuga]

That is very old school teaching. The vast majority of high incident energy locations are due to extremely long exposure times due to there not being enough fault current to cause the protective devices to open quickly or someone not being able to move away from the arcing location.
For at least 6 years the PPE manufacturers have made equipment well in excess of 40 cal/cm^2.

One valid area of concern is the effects of the Arc Blast, how there is still no industry standard methodology for predicting a blast value.

That is a very spot on, some of the mills here have changed from 480 to 600 over the years, when I got to ask an engineer why I was told something to the effect that one of the reasons was 600V was actually safer than 480V in terms of less fault current and quicker clearing times.

 

[David Castor]

So an unplanned outage which could last for days or even weeks is a lesser hazard than scheduling an outage?

That's all part of the risk assessment. You're always free to decide to take an outage if you feel that is the lesser risk overall. I'm just telling you what it says.

 

[David Castor]

The 70e instructor said that, anything needed above a 40 cal suit was worthless because the compression blast would kill you by crushing, not the burn.

This is really not accurate and there is nothing in NFPA 70E that says that. It's possible that the pressure wave from an arc-flash event could injure or kill someone, but there isn't much data to indicate when this might occur. Also, there's nothing in NFPA 70E that says you can't work when the incident energy exceeds 40 cal/cm2.

 

[hillbilly1]

This is really not accurate and there is nothing in NFPA 70E that says that. It's possible that the pressure wave from an arc-flash event could injure or kill someone, but there isn't much data to indicate when this might occur. Also, there's nothing in NFPA 70E that says you can't work when the incident energy exceeds 40 cal/cm2.

They do have security videos showing it, just saying.

 

[garbo]

Arc flash incident energy labels are not a requirement of any enforceable code which is part of a permitting process.

Arc Flash labels are one option, and the most popular one, companies can use to satisfy OSHA and insurance worker safety requirements.

Thank you for letting me know this.

 

[LarryFine]

I hate working on anything hot.

 

[jim dungar]

They are somewhat enforceable with the new language in 110.16(B) in the 2023 code.(B) Service Equipment and Feeder Supplied Equipment

Does this section require arc flash incident energy labeling at any place other than the 'service equipment'?

What about those companies that chose the NFPA 70E option of using the tables and categories rather than actual calculated incident energy values?

 

[don_resqcapt19]

Does this section require arc flash incident energy labeling at any place other than the 'service equipment'?

What about those companies that chose the NFPA 70E option of using the tables and categories rather than actual calculated incident energy values?

It applies to both services and feeder supplied equipment rated 1000 amps or more.

Do the places that use the tables and categories post that information on the equipment? If so, I think that would comply.

 

[jim dungar]

It applies to both services and feeder supplied equipment rated 1000 amps or more.

So the NEC does not require arc flash labeling except in those situations that might also require Arc Flash reduction switches.

Do the places that use the tables and categories post that information on the equipment? If so, I think that would comply.

No labeling of specific equipment is required by NFPA 70E, but employees must be told what PPE is required. The easiest method is usually labels, but specific incident energy levels are only required if calculations have been performed.

What information does 110.21(B) require?

 

[don_resqcapt19]

So the NEC does not require arc flash labeling except in those situations that might also require Arc Flash reduction switches.


No labeling of specific equipment is required by NFPA 70E, but employees must be told what PPE is required. The easiest method is usually labels, but specific incident energy levels are only required if calculations have been performed.

What information does 110.21(B) require?

The arc flash labeling starts at 1000 amps and the arc flash reduction rule starts at 1200 amps,

It is my opinion that the "applicable industry practice" will require the actual incident energy level and arc flash boundary on the equipment. The NEC wants to require you to use the 70E label, but the NFPA rules do not permit on NFPA document to require the use of another NFPA document, hence the "applicable industry practice" part of the rule. If there is another "applicable industry practice", you could use that, but I don't think that there is another.

110.21(B) does not require any specific information. It simply provides requirements as to the type and installation of labels that are required by other code sections.