Panel board sizing

[backintheblue]

This question kind of approaches this subject from the back side.

I have a project where there is a 480vac drop, but no panel boards. We want to install a transformer and panel board to get 120/208 for general use receptacles.

The drop is 480vac/100amp. I back calculated the maximum transformer size to be 83KVA. We'll use a 75KVA. The secondary will be about 200amps, if I did my calculations correctly.

The question is this. Based on this information, what is the maximum panel board size that I can attach to this service?

[bobelectric]

225 amp @ 208/120 3 pf

[480sparky]

Originally Posted by backintheblue

..........The drop is 480vac/100amp. ......... what is the maximum panel board size that I can attach to this service?

100amps?

[Magnettica]

Don't worry too much about what the POCO is is supplying you with now. Provide them with a real load calculation and they will determine which size wires to run to your service.


But for kicks... (I x E = P)

(480V x 1.732) x 100 amps = 83Kva

83,000va/ (208V x 1.732) = 231 amps

Looks like you're good to go with what's there but you'll still need to supply the calc load to the poco.

[alyna]

Originally Posted by bobelectric

225 amp @ 208/120 3 pf

I second this suggestion. I guess,it is safe enough.

[Dennis Alwon]

You can attach any size panelboard you want it is the OCPD that makes the difference.

[raider1]

Originally Posted by Dennis Alwon

You can attach any size panelboard you want it is the OCPD that makes the difference.

As long as the rating of the panelboard meets or exceeds the rating of the overcurrent protective device protecting the panelboard.

Chris

[wayne g]

Second the motion