Changing 40A circuit to 20A double pole

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  #1  
Old 07-04-11, 08:16 AM
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Changing 40A circuit to 20A double pole

I have a question that I haven't completely found the answer to on other posts...

I have a 40A circuit breaker, Square D box, that was previously used for a oven/microwave combo. I took that out and will be replacing it with a countertop plug in microwave. It will be semi-built in with a trim kit in a cabinet and the only thing I plan to run from the circuit is the microwave. There is already a separate 40A circuit going to my new range. I would like the keep the existing 8 gauge wire, pigtail it to 12-2 in a junction box, then run the 12-2 Romex to a 20A receptacle. That receptacle would be at the back of a cabinet. The microwave would plug into it and then have a trim kit to cover the opening of the cabinet.

I know I can't wire the 40A circuit directly to a 20A outlet. My proposed solution is to replace the 40A breaker with a 20A double pole breaker to make 2 circuits. The 8 gauge wire would be a multiwire with the black as one 20A/120V hot and the red would be another 20A/120V hot. They would have a common neutral and ground. I would take the black, neutral, and ground wires and connect to the 12-2 in the junction box. I would cap the red wire, connecting it to nothing, and make it an unused circuit.

Does this make sense? Will it work safely? I know it would be underusing the potential of the 2 circuits but I'm looking for the easy (& safe) solution to plugging in the microwave. Does it work to have the 8 gauge wire as multiwire with 20A double pole circuit and 20A receptacles?

Thanks for your help! I'm in West Virginia.
 
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  #2  
Old 07-04-11, 08:42 AM
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Sounds good. If you break the tab on a duplex receptacle, yo can wire the top half to red and the bottom half to black. You can use the other half to plug in uc lights or something similuar.
 
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Old 07-04-11, 09:05 AM
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Justin"s suggestion in this case won't work because in a kitchen you need a GFCI and they can't be split but your suggestion will. Be sure the box the splice is in remains accessible.
 
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Old 07-04-11, 09:56 AM
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Ray, Justin's idea will work just fine IF instead of splitting a single duplex receptacle the original poster uses the Multi-Wire Branch Circuit to feed two separate GFCI receptacles.
 
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Old 07-04-11, 10:05 AM
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Originally Posted by Furd View Post
Ray, Justin's idea will work just fine IF instead of splitting a single duplex receptacle the original poster uses the Multi-Wire Branch Circuit to feed two separate GFCI receptacles.
Yes. I was only responding to the narrow confines of his statement.
 
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Old 07-04-11, 10:22 AM
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Doesn't a large cable like that use a 2 gang box or a 4x4 box with a mudring, anyway?
 
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Old 07-05-11, 08:00 AM
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If the receptacle does not serve the countertop it would not need GFI protection.
 
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Old 07-05-11, 08:12 AM
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That was what i was thinking when i posted.
 
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