This week's topic still stirs up a debate from time to time.

According the 2012 Edition of NFPA 130.7 (A) INFORMATIONAL NOTE NO. 3.

When incident energy exceeds 40 cal/cm^2 at the working distance, greater emphasis may be necessary with respect to de-energizing before working within the limited approach boundary of the exposed electrical conductors or circuit parts.

I highlighted "Informational Note" to emphasize this is technically not enforceable as requirements of the standards.

This week's question:
Do you consider 40 cal/cm^2 as a firm cut off where no energized work can be performed?

• Yes
• No
• Depends on the situation

Can I vote twice? Technically no but without further guidance on arc blast and with this informational note hanging out there, it places everyone in a situation where it has to be treated as enforceable even when it is not. No guidance is given to "greater emphasis". I really dislike statements like that in Codes because they always result in going to the most conservative approach.

Some believe that this somewhat enforces equipment/task redesigns driving down the incident energy. The issue with this is that for instance if you have gear >15 kV, and you follow IEEE 1584 to the letter, this leaves you with using a theoretical calculation method which is grossly conservative, at 3X the actual tested values at 15 kV, and continues to become exponentially worse as voltage increases. Without a competing standard for >15 kV out there, the only other viable calculation method is ArcPro, which is widely recognized but closed source and does not have a shred of support in standards, journals, etc.

ArcPro is known to be the source behind the tables in the NESC. So there's at least a commonly used standard which supports it. Far from the same thing as a peer reviewed method, but more than nothing.

I voted "depends on the situation". Performing actual live work, i.e. direct contact, exposure etc. - Not permitted. However, tasks such as operating equipment, opening closing breakers etc. i.e. "interaction" there often isn't much of a choice when you are trying to create an electrical safe work condition. (Although I'm sure Zog has a better method )

I voted Yes beacuse as the one responsible for my field crews you have to draw the line somewhere, if it is >40cal find another way (Usuallly means get remote devices out there), if there is no other way then don't do it at all.

I vote yes but I wonder if it will ever become code. I imagine (based on my experience) there are many places out there that accept the dangers simply because it is not against code. While this practice is probably not in the companies best interests, it is still reasonable as a management view. "If it were that dangerous, the code would explicitly prohibit it." I would like to propose a question of the week of whether or not it should become code to prohibit live work over 40 cal. Obviously there would be a need for exceptions but it needs to start somewhere.

If you have a firm cutoff, you have a problem. It's not deenergized until it's tested, but you can't test because it's not yet deenergized. The only possible answer is no.

Oh yeah, that elephant in the room, I change my answer to yes.