COMMUNITY FORUM

jam92102

05:28PM | 06/07/05
Member Since: 10/02/04
20 lifetime posts
Bvelectrical
Hi i'm wiring a subpanel into my garage off of a 50 amp double-pole single throw breaker in my box. I'm using 6 gauge wire and runing it to the main breaker on the sub panel. My question is will the main breaker on the sub panel need to be a 100 amp breaker or a 50 amp. I figured I would have two 50 amp wires running into that box so I would need a 100 amp breaker correct? If I'm not being clear just let me know. THanks for any advice you all can give.

Jim

Jarrod

05:44PM | 06/07/05
Member Since: 04/12/05
15 lifetime posts
The 50 amp 2-pole breaker in your main panel does not provide 100 amps (50 * 2). The two poles are connected to the two phases of your electrical service. Phase A is 120 volts to ground, phase B is 120 volts to ground. However, because the two phases are 180 degrees apart, there is 240 volts between them (picture two arrows pointing in opposite directions, each 120 units long). So, your 2-pole breaker is providing 50 amps at 240 volts. Twice the power as 50 amps at 120 volts, but still just 50 amps.

As for the size of the main breaker in the sub-panel, it really doesn't matter. If the sub-panel main breaker is larger than 50 amps, the circuit will still be limited to 50 amps by the feeder breaker in the main panel.

Jarrod

jam92102

07:22AM | 06/08/05
Member Since: 10/02/04
20 lifetime posts
Thanks for the info Jarrod. As far as the main breaker in the subpanel, do I have to worry about having too big of a breaker or is it more like a switch. If for some reason I get too much of a load the breaker in the main box will trip correct?

Jim

Tom O

10:53AM | 06/08/05
Member Since: 09/17/02
477 lifetime posts
Jim,

Using a 100 amp breaker out at your sub-panel should not pose a problem. The only thing you need to check for is that the lugs on the breaker are listed for the size of wire that you plan on using. This will be marked on a really tiny label on the breaker or it will be marked on one of the labels in the breaker box. Chances are, #6 will be OK, but you never know.

If you'll send me your e-mail address, I'll send you a FAQ sheet on sub-panels installed in remote buildings.

Tom

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