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I went to replace the over-range microwave today, only to discover that the old one ran on a 220V line:

old outlet

...but the new one only needs a 110V receptacle:

New microwave plug

Am I correct in assuming that I can use the existing wiring, swap the 220V outlet for two 110V two-outlet boxes, and then remove the 220V breaker in the box for a single 110V breaker (40 amp down to 20, I think)? Is this advisable? I know DIYers who swap out breakers all the time, but I'll need to do some reading before I tackle that...

  • You are basically going to reassign 2 wires and a ground for your circuit and cap the fourth wire at both ends? You seem to understand the need to put in a smaller breaker to match the new outlet. That sounds good to me. – Zach Mierzejewski Sep 19 '15 at 21:33
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What size are the wires? A 40 AMP circuit is probably 8 or 10 AWG, neither of which will likely fit in the terminals of a 20 ampere receptacle. Which means you'll have to use a 12 AWG pigtail, to attach the receptacle to the circuit.

Aside from that, you've got it about right.

  • Remove the existing receptacle.
  • Install a new box.
  • Use properly sized twist-on wire connectors to attach a 12 AWG pigtail to one of the ungrounded (hot), the grounded (neutral), and the grounding conductors.
  • Use a properly sized twist-on wire connector to cap the extra ungrounded (hot) conductor.
  • Remove the double pole 40 ampere breaker.
  • Install a single pole 20 ampere breaker.
  • Connect one of the ungrounded (hot) conductors (the one attached to the receptacle), to the new breaker.
  • Use a properly sized twist-on wire connector to cap the extra ungrounded (hot) conductor.
  • Install a plate to cover the empty hole in the panel cover (that was created by removing the double pole breaker).

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