Microwave Circuit Breaker Keeps Tripping

Thread Starter


Joined Sep 26, 2014
Hello Folks. Why would a replaced microwave keep tripping+?

I have a customer who replaced his over-the-range microwave with a new, 1000 watt one. The old one was hard-wired and the new one has a plug. So he used the connector like this:


I guess I'm a traditionalist and would have rather have seen wires correctly connected to a junction box and outlet. Regardless, circuit keeps tripping every three weeks at "night time" when they turn on a few kitchen lights (and the backyard lights kick on) and the microwave (trips when they turn on the microwave.) The connector screws were color coded so he assured me the wires were properly wired. I asked him to feel for the microwave plug/wires and connectors and its wires for excessive heat. I'll be checking for good grounding at the panel when I'm on the jobsite.

The circuit that keeps tripping is 15 amps and the outlets serviced are the kitchen lights, microwave, part of the family room and the outdoor patio "flood" lighting. The customer replaced all bulbs with LEDs on this circuit but already I sense that he's creating an overloading. But he installed the new microwave 6 months ago and that's when the problem started occurring. No other appliances on that circuit are new.

I had him turn on everything in the house and identify some of the circuits. There is a 20 amp circuit that goes to a second living room that has only a lamp plugged in.

I would like him to try plugging in the microwave in a different circuit but that would require an extension cord and may cause some voltage drop so that may not be possible.

So my plan is to switch circuits with the 15 and 20 amp circuits mentioned, to give him 5 extra amps and see if that works. I'll check the grounding on these before proceeding as well. The 15 amp circuit breaker may be on the blitz, too, I imagine.

Regardless of my plans, any ideas of what might be causing this and the solution???
Last edited:


Joined Apr 2, 2009
You are overloading the breaker.
If the wire can withstand the new microwave current demand you can upgrade the breaker to 20 Amps.
Better way is to wire a new circuit from to DB to microwave


Joined Jun 26, 2012
FWIW here's the cutsheet on the connector. It's designed for round portable service cords. Solid isn't spec'd.
If the breakers are combo arc/ground fault type, I've found that loose connections at the outlets will cause tripping.
http://www.legrand.us/-/media/brands/passandseymour/resources/specification/industrial/sb-plugs-connectors-and-turnlok/sb heavy duty maxgrip m3 plugs connectors spec sheet sf502r2.ashx

I'd for sure check it out and try to talk him into a proper outlet and old-work box:

Good luck.