How does your Plant LABEL the 2000A Short Circuit Amp IEEE 1584 2018 exceptions? 1

[bdn2004]

The Plant I'm working for just adopted this new standard even though it's a couple years old.

And I'm running into this common situation: The short circuit current at some 208V disconnect switches is only like 300A, and on its upstream molded case circuit breaker it times out to the 2 sec max - and the calculation gives a high incident energy.

But then you've got this exception - under 2000A SCA, it won't sustain an arc....What does your Plant put on the labels ? 0.0 Incident Energy? or NO ARC FLASH HAZARD? What if you get a low energy number anyway by the standard method? Say like 0.5 cal^cm2 , do you use that or is it really NO ARC FLASH HAZARD?

 

[dpc]

Our recommendation would be to label something like this for 4 cal/cm2. IEEE 1584-2018 doesn't say there is no hazard for bolted fault currents below 2000 A, in fact it says that sustained arcs are possible, but less likely. The equations can be applied down to 500 A of bolted fault current at 208 V.

4 cal/cm2 is a reasonable assumption for a maximum incident energy at 240 V and below. If you use a maximum arc time of 2 seconds, the calculated energy will likely be less than 4 cal/cm2 in most cases for these 208 V applications. If the Categories Method in NFPA 70E is used, you generally will end up with Category #1 at 240 V or lower. This is effectively 4 cal/cm2.

The main goal is to have the worker in PPE that will protect them, not necessarily to make the most accurate arc-flash calculation. I would never put on a label that said NO ARC FLASH HAZARD.

 

[bdn2004]

dpc,

That’s a great and wise answer but frustrating at the same time. You oughta be on one these code making panels.

Cause to me it’s ambiguous information. “Are possible but less likely”..No faults are likely events. Wouldn’t it be easier just to say “under 2000A short circuit default to 4 cal/cm^2.

I’ve heard it explained that the energy is so little that it cannot sustain an arc...and if is truly the case: then there is not an arc flash hazard. Obviously that’s not true. I’m going with the higher number. What’s in it not to ?

 

[dpc]

(I made a couple of edits to my original comments) I'm not defending what is in IEEE 1584, but it is intended to be a GUIDE for calculations. It doesn't really address specifics of PPE. Also, consider a case where the worker creates a fault with a screwdriver or some other tool in a 208 V panelboard. Even if the arc is not sustained, there will likely be molten metal droplets ejected towards the worker. This is seen in testing and real-world events. So it is difficult to state that there is no hazard. Going with 4 cal/cm2 requires face shield and balaclava along with with gloves, etc. So they should be protected.

It's low risk, but not really zero risk. And it is relatively simple to protect against the hazard - so why not do it. The electricians will complain no matter what you do.