AIC

[klarenj2003]

I landed a 200A 120/240V ,1/0 panel in a building , with 140' of 250-250-3/0 URD underground to it , From a tap box that is fed from a pad transformer. how do you calculate a AIC rating of that 200A panel

 

[Pharon]

You need to know the kVA and impedance of the transformer.

 

[jim dungar]

I landed a 200A 120/240V ,1/0 panel in a building , with 140' of 250-250-3/0 URD underground to it , From a tap box that is fed from a pad transformer. how do you calculate a AIC rating of that 200A panel

You calculate the available short circuit current (SCA). Then you choose an AIC that is higher.

To calculate the SCA you need to know the starting available short circuit current. Have you gotten anything from the utility yet?

 

[mgookin]

I landed a 200A 120/240V ,1/0 panel in a building , with 140' of 250-250-3/0 URD underground to it , From a tap box that is fed from a pad transformer. how do you calculate a AIC rating of that 200A panel

Call the construction division of the POCO. They'll give it to you.

 

[don_resqcapt19]

Typically the utility will give you the available fault current at the secondary terminals of the transformer that supplies the service. If that number is lower than the short circuit rating of the equipment, I just mark that number as the available fault current on the equipment.

If the number from the utility is close to, or higher than the equipment rating, you can do the calcs to see how much the impedance of the wire run has reduced the available fault current at the line side of your service equipment.

Bussmann has a nice app that will do the calculations.

 

[kwired]

conductors between tap box and transformer will also have impact on the result at your load end, so you would need to know size, type and length of those as well and figure that segment of the run into it.

 

[mwm1752]

My chart shows a single phase transformer is rated approx 20,000 AFC at 100KVA & 3 phase apporx 20.000 AFC @ 150 KVA -- so most Main OCPD are usually 20,000 AFC rated -- the 140' of run will drop the rating requirement by a major percentage -- Unless you have a fairly large transformer you should be good. I am not saying that finding the proper way of calculating is not a good thing.