Arc flash calcs for transfomers smaller than 125 KVA

steve66

Senior Member
I'm wondering if 208V panels feed from transformers still need to be included in an arc flash study.

I know IEEE 1584 mentioned something about transformers smaller than 125 KVA, but it seemed to be a hot topic of debate. It looks like the 2018 version of the IEEE 1584 is in the draft version, but not the final version.

Does anyone know if the exception (if you can call it an exception) will still be included?

I know EasyPower still has some info. on their website that says transformers less than 125KVA don't usually need to be included in an arc flash study.
 

wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
The 125kVA and 240V exemption goes away with the new IEEE 1584 version. It appears to be being replaced with an amperage cutoff of 2000A.

The new version is winding its way thru the approval process and is likely to be issued by the end of the year.
 

wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
2000 amps is not really alot of fault current. I have seen over 10kA of fault current on 208Y/120V circuits which will exceed the rating of many non-fused disconnect switches.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I've been to a couple of Jim Phillips' classes:
He likes to blow things up.
He gets distracted by shiny objects.
NFPA 70E writers don't like him.
Explanations are clear, uses lots of examples.​

What's not to like?
 

steve66

Senior Member
2000 amps is not really alot of fault current. I have seen over 10kA of fault current on 208Y/120V circuits which will exceed the rating of many non-fused disconnect switches.
Right, but you didn't mention that was a fault current. :)

You just said "amperage cutoff of 2000A", which to me sounded like an ampacity rating. As if the exception now applied to a 1600 amp panel.
 

wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
Sorry, I just assumed since it was a discussion of arc flash, which is due to a fault, and the calculations for incident energy are based on fault current, that it was a given that I was referring to fault current. I will strive to be more clear in the future.
 
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