# Panel board sizing



## backintheblue (Nov 11, 2010)

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?


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## bobelectric (Feb 24, 2007)

225 amp @ 208/120 3 pf


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## 480sparky (Sep 20, 2007)

backintheblue said:


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


100amps? :blink:


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## Magnettica (Jan 23, 2007)

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.


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## alyna (Nov 23, 2010)

bobelectric said:


> 225 amp @ 208/120 3 pf



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


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## Dennis Alwon (May 9, 2009)

You can attach any size panelboard you want it is the OCPD that makes the difference.:whistling2:


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## raider1 (Jan 22, 2007)

Dennis Alwon said:


> You can attach any size panelboard you want it is the OCPD that makes the difference.:whistling2:


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

Chris


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## wayne g (Nov 28, 2010)

Second the motion


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