240v to 120v in junction box?

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Old 01-26-18, 06:34 PM
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240v to 120v in junction box?

The power for the microwave is on a 20 amp circuit that starts off on a 240v cable, gets converted into a 120v (12g) cable in a junction box, where it then goes to connect to the microwave. The microwave uses 14amps, so I know the breaker is ok but I'm not sure about the cabling.

Should I change the cabling to 12 gauge from the breaker to junction box, or is the current set up okay?
 
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Old 01-26-18, 08:35 PM
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What do you mean by 240V cable ?
Are you referring to 12/3 ? It will have black, red, white, and bare ground.
If one of red or black wire goes to microwave and one of red or black wire goes to a kitchen outlet and both shares white (neutral) wire, then you have what is called Multi Wire Branch Circuit (MWBC).

You are perfectly fine if this is the case.
 
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Old 01-27-18, 12:11 AM
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It sounds like someone used an abandoned electric oven or cook top circuit to feed the microwave.
It's OK to use the larger cable from the panel as long as the cable is 3-conductor with ground.
The microwave needs a neutral, one hot wire, and a ground.
Also check to make sure the old cable is not aluminum. If it is aluminum you will need some special connectors.

You should also answer lambitions question, are both hot wires of the cable in use or is one capped off?
 
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Old 01-27-18, 07:57 AM
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Looking at the circuit panel, the cable is copper 12/3 and the red wire is in a wire nut. So it goes Panel > 20A > 12/3 > Junction Box > 12/2 12g > Microwave.

 
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Old 01-27-18, 08:12 AM
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As long as the wire is properly sized to the breaker you are fine. All the wire is #12 which is good for 20 amp circuits. I would be happy to have the extra circuit available in the kitchen.

On a side note: As electricians we quite often mix multiple voltages, circuits, amperage and wire sizes in boxes and raceways. As long as everything is properly protected it is all good.
 
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