IEEE-1584 and 125KVA 208V

[lile001]

I have heard that IEEE-1584 suggests that 208 V systems 125 kVA and larger be evaluated for arc-flash hazard using their calculation method. I was just pouring through this document, looking for this reference. Is this implying that 208V systems under 125KVA do not need to be evaluated? Just for fun I did a calc based on a 2000KVA service entrance, 125KVA dry transformer to a 208V panel, and the arc flash came out signifigantly high. My questions are:

Where does IEEE-1584 say this?

and

Why does it say this?

 

[Zogzog]

Yes it does say that, section 4.2 (Page 6)

What other factors did you use for your calc? What program did you use? Clearing times? What did you get for a result?

 

[lile001]

I was using SKM, and I just assumed some values for a molded case circuit breaker that would be common in such a case, since it was just an excercise. It made me question the 125KVA cutoff, though. Is this really meant to be a cutoff, that Arc Flash Hazards become negligible below 125KVA? I find that hard to believe.

 

[rbulsara]

It is not as simple as it seems. The short answer is the field incidents supports that assumption and IEEE std has not tested those systems for the same reasons.

Try to attend seminar on arc flash by Univ. of Madison, WI, USA.

Also see my response in thread242-135507 and search for other threads on the topic.

 

[dpc]

It does says this and the reason is basically trying to be consistent with available test data.

So, yes for a 208/120V system served by a transformer smaller than 125 kVA, IEEE 1584 says no arc-flash calculations need to be done.

But, NFPA 70E does not exactly give you a free pass. I would still label the equipment as a potential arc-flash hazard.

 

[lile001]

Right - NFPA 70 Table 130.7 rates most energized work on panelboards under 240V as risk category 1. Maybe if one were doing arc flash calculations, you could take the worst case, and if IEEE 1584 doesn't address these panels, you just label them as Category 1.