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#32851 - 01/04/04 01:56 PM Subpanel Calculation
Nebraska Offline
Junior Member

Registered: 01/03/04
Posts: 1
Loc: Grand Island, NE, USA
I recently added a sub panel to my house It contains 3 15 amp breakers, 2 15 amp tandem breakers, 1 20 amp breaker and 1 2 pole 30 amp breaker for a water heater, all the 15's and the 20 are for general purpose receps. How do you calculate the size of breaker to put this sub panel on. Taking 80% of all the breakers added together just doesn't seem right, maybe it is though. Please help me. Thank you.

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#32852 - 01/04/04 02:16 PM Re: Subpanel Calculation
earlydean Offline

Registered: 12/22/03
Posts: 749
Loc: Griswold, CT, USA
You got the cart before the horse. First, you compute the combined loads, using diversity factors allowed by the NEC. Second, you choose a panel of a size adequate for the loads just computed. Third, you choose a feeder of ample size. Fourth, you choose a circuit breaker sized to protect the feeder and panel.

Or, take the shortcut: size the breaker for the size of the new panel (usually 100 or 60 Amps)and feed with 100 or 60 Amp wires.


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