Arc flash calcs for transfomers smaller than 125 KVA

[steve66]

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.

 

[jumper]

Isn’t that in 70E also? If not, it was.

Maybe I go look.

 

[jumper]

It used to be in 130.3. I did not see it in the 2018 70E, but I checked 2009 and it was there.

Moved or gone, IDK.

 

[dkidd]

A good source for arc flash information is https://brainfiller.com/arcflashforum

 

[wbdvt]

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.

 

[steve66]

Thanks for the responses. That does look like a good forum for arc flash.

2000 amps sounds like a lot?

I'm going to have to watch this:

https://www.ecmag.com/ecmag-live/2018-ieee-1584-update-introduction-changes-jim-phillips

 

[steve66]

https://www.ecmag.com/ecmag-live/2018-ieee-1584-update-introduction-changes-jim-phillips

Jim starts talking about this at about 35:20. The 125 kva "exception" is basically gone, and has been replaced with some mention that below short circuit currents of 2000 amps, sustaining arcs are less likely to occur.

 

[wbdvt]

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]

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]

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]

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.

 

[Phil Corso]

Ezdrocks...

What is the Hazardous Area classification in which the Xfmr is located?

Phil Corso