Wire size for an Transformer

[buttcrimp]

Please double ck my math
I have a 400 amp 1 Ph lighting panel that is 250' from my mcc. The size transformer I come up with is a 150 KVA. My supply is 480v 3Ph. The wire size I came up with is 350 mcm with XHHW Ins. And my volatge is 2.65% total. My question is this correct??

 

[jtester]

Re: Wire size for an Transformer

I am not sure I understand your question. It sounds like you have a 400 amp single phase panel fed from a stepdown transformer. Is that correct? What is the single phase panel voltage, 120/240?
150 kva is a three phase transformer size, and 350 kcmil is only good for 310 amps, which doesn't seem to match with any of the above either.
If you can post some more info, I'll try to help.
Jim T

 

[buttcrimp]

Re: Wire size for an Transformer

This project was thrown in my lap and now I'm trying to size the wire to the step down transformer plus sizing the disconnect breaker. They have not given me any Information on the Transformer as far as KVA I'm trying to size the transformer that would be installed.
yes it is a 400A 120/240VAC lighting panel.

 

[jtester]

Re: Wire size for an Transformer

400 amps at 120/240 400x240=96,000va or 96KVA
A 100 KVA transformer should be more than enough for a 400 amp panel. I would suggest that you run 480 single phase the 250' to the panel location and install a transformer there. The 480 circuit to the transformer could be 96,000va/480v = 200 amps or #3/0 THHN/THWN cu per Table 310.16, and a 200 amp breaker would be adequate.
I would suggest paralleled 3/0 on the 240 side of the transformer since you have a roll of it there for the 480 feeder anyway.
Hope that helps.
Jim T

 

[buttcrimp]

Re: Wire size for an Transformer

Thanks for the info it helped alot..