Amp load @ 240V vs 120V

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Old 04-14-10, 10:47 AM
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Amp load @ 240V vs 120V

Quick question for all of you, I know the question of whether a panel rated for [email protected] can supply [email protected] has been beaten to
death and is always a great argument starter. Here is a more realistic example,

If you have a subpanel fed by a 50amp dual pole breaker. Can this panel actually pull 100amps worth of 120V circuits.(Ignoring the 80% rule, balancing and such). This is due to each leg of the dual pole being able to supply 50 amps?

To simplify even more, could this panel have 5 fully loaded 20 amp circuits?
 
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Old 04-14-10, 10:53 AM
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Originally Posted by rhiggins View Post
Can this panel actually pull 100amps worth of 120V circuits.(Ignoring the 80% rule, balancing and such).
Yes.

To simplify even more, could this panel have 5 fully loaded 20 amp circuits?
Yes.

In questions like these, it helps to convert to power (watts) so you are comparing the panels on level ground.

50A * 240V = 12,000W available at the panel

100A * 120V = 12,000W consumed by the circuits

Assuming perfect balance, and ideal breakers the power consumed is exactly equal to the power provided.
 
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Old 04-14-10, 10:55 AM
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ibpooks, thanks for the clear answer, that is what I thought. Now to complicate things more, once you start loading a panel based on watts available, balancing becomes important, correct?
 
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Old 04-14-10, 10:58 AM
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If the load is close to the panel's limit, then yes balancing is a major issue. The panel also operates a bit more efficiently when balanced.

In your example, you could not have 60A on leg A and 40A on leg B because that imbalance would exceed the 50A feeder; however, 50A on leg A and leg B would be acceptable even though both configurations are 12kW.
 
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Old 04-14-10, 11:28 AM
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Thanks so much for your help!!
 
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