AIC Calculations

[don.mckee@hotmail.com]

I have a 120/208V, 3PH service with an AIC rating of 37,510 at the transformer. How do I figure the AIC rating of the new 800 A disconnect if I have a 265' parrallel run of 600 MCM?

 

[mayanees]

Fault Current at 800A disconnect

Fault Current at 800A disconnect

Don,
I use SKM PowerTools for Windows.
Worst-case looks like 13,739 amps.
JM

 

[davidr43229]

in the worst case, you can not use 10,000AIC molded case breakers downstream, if that math works out. You either need to up the AIC rating of the breakers, or introduce current limitation ahead of those 10KAIC breakers.
Try this and see if it helps you.
http://cooperbussmann.com/7/FreeSoftware.html#Short-Circuit Current Calculator
Just my $.02

 

[hdpeng]

Cooper Bussmann used to have a very good (& free!) PDF manual for short-circuit calcs posted on their website under the literature section, but it's not there anymore (or at least I can't find it). You might want to contact them directly & see if you can get a copy of their 'Electrical Plan Review' manual they used to have on there.
Anyway, just running the calcs by hand using point-to-point RMS sym. method (like some of us old eng's still do & which is obiously a little more conservative), & assuming copper cond's/PVC C., I get 15,147A.

AH-HA! Here's the link. I found it on someone else's posting: http://www.bussmann.com/library/docs/EPR_Booklet.pdf

Thanks to Ron, Senior Member.

 

[benaround]

HDP,

A quick 'Thank You' for that Bussmann link, that's a lot of good info on 1 doc.

 

[ryan_618]

I agree with Angus Young, er...I mean hdpeng, the bussman site has great information and free stuff for this type of work.

 

[benaround]

hdpeng , I think Ryan is saying WE SALUTE YOU.

 

[ryan_618]

hdpeng , I think Ryan is saying WE SALUTE YOU.

Ride on....

 

[hdpeng]

http://ecmweb.com/mag/electric_shortcircuit_calculation_methods/

Here's another link to more good fault current calc info from ECM.

 

[Jraef]

in the worst case, you can not use 10,000AIC molded case breakers downstream, if that math works out. You either need to up the AIC rating of the breakers, or introduce current limitation ahead of those 10KAIC breakers.
Try this and see if it helps you.
http://cooperbussmann.com/7/FreeSoftware.html#Short-Circuit Current Calculator
Just my $.02

He said an 800A disconnect, not a breaker. But really, does anyone even make an 800A CB with only 10kAIC? Lowest I know of is 35kAIC on that size.

don.mckee
I don't know of any non-fused disconnect switch with an AIC rating of more than 10kA all by themselves. But if you have upstream fuses or are thinking of a fused disconnect, then most of them are rated for whatever fuse they are used with. So for instance if you use one with Class RK1 fuses, it should be rated for 200kAIC. In other words way more than you have available anyway.

 

[adavey]

Is the POCO changing the size of the transformer ????? If so you would need to re-calculate the available fault current based on the new transformer KVA and impedance ratings.

 

[kingpb]

I have a 120/208V, 3PH service with an AIC rating of 37,510 at the transformer. How do I figure the AIC rating of the new 800 A disconnect if I have a 265' parrallel run of 600 MCM?

Could you clarify which side of the transformer you have the fault current on.

Also, where did this info come from, what is the KVA rating and impedance of the transformer?

Without making a bunch of assumptions, the information provided is not enough to accurately help to answer your question.