Bought a KitchenAid KMBP107ESS20 built in convection microwave to replace old GE built in convection microwave. Wiring is a dedicated circuit 20A circuit with 3 wires (black, white, ground) New appliance is a 120/240V, 20A, and has 4 wires (L1, L2, N, and G) How do I properly wire this 4 wire to existing 3 wire.

When installed, they left the red wire disconnected. My convection oven takes an hour to heat up and goes off prior to fully reaching temp. I think this may be due to them improperly wiring the appliance.

  • What do the instructions say for wiring it to a 3-wire/120v circuit? Does the microwave really need 240v for heating and uses 120v for control/display? It's possible that they (whoever "they" are) didn't install it properly and that you'll have to upgrade the circuit to a 4-wire 240v circuit to truly get this new one to work. Or, return it and get one that'll run on only 120v.
    – FreeMan
    Nov 8, 2023 at 18:22
  • It does not give instructions for wiring it to a 3 wire. The microwave heats fine, the convection just not working well. I had a recommended handy man install. Nov 8, 2023 at 18:54
  • The electrical requirements state that the oven is rated 12/240 V, 20A. Under Voltage it lists 240 VAC 19.9 A/3250 W or 208 VAC 19.9 A/3250 W Nov 8, 2023 at 18:55
  • You will also need at least a 25amp breaker and 10 gauge, three wire plus ground cable/wire if doing it your self(allowed only for your own single family home in some places).
    – crip659
    Nov 8, 2023 at 20:18

1 Answer 1


I believe that the 120v portion of the electrical requirements is for the electronics (and possibly the microwave portion) of the appliance only.

It will take 240v to properly heat in convection mode just like any other oven. This means that you cannot run it on a 120v breaker and expect it to cook dinner in convection mode any time this week.

You will have to DIY (or hire a licensed electrician) to install a 240v circuit with proper 4-wire cabling to make this work as advertised. Unless your handyman is a licensed electrician, he is not legally allowed to do electrical work in your house.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.