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Old 11-11-2010, 12:24 PM   #1
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Default Panel board sizing

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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Old 11-20-2010, 06:21 PM   #2
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225 amp @ 208/120 3 pf

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Old 11-20-2010, 06:30 PM   #3
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Quote:
Originally Posted by backintheblue View Post
..........The drop is 480vac/100amp. ......... what is the maximum panel board size that I can attach to this service?
100amps?
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Old 11-20-2010, 08:48 PM   #4
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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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Old 11-22-2010, 10:47 PM   #5
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225 amp @ 208/120 3 pf

I second this suggestion. I guess,it is safe enough.
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Old 11-23-2010, 08:05 AM   #6
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You can attach any size panelboard you want it is the OCPD that makes the difference.
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Old 11-23-2010, 10:41 AM   #7
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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.

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Old 12-05-2010, 06:45 PM   #8
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Second the motion

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