Why does new 1700 watt microwave keep burning out my 20amp dedicated breaker?

[Toddvandy]

20amp outlet, 20amp breaker, 14 gauge wire. I suspect I need a larger wire but that’sa lot of trouble to go through without being sure.

 

[Megawatt]

It did turn black. What I’m not clear about is if it had something to do with 12 gauge connecting to a 14 gauge and overheating with the amount of power the microwave was drawing, or if when I remodeled and reset the box the wire in the attic moved and pulled out of the nut just slightly? Either way, it doesn’t explain why replacing the breaker worked-/at least until it didn’t. After running another 12 gauge off the wire to the microwave yesterday, everything seems to be working normally now. I’ve even got the gas stove plugged in to it. Hope it stays this way, and I’m using the breaker I thought was broken. Thanks so much for your help and I’ll reply again if there are further issues.

What your problem was it wasn’t as much as the wire splicing from 14 to 12. We have dumb a— people who do electrical work and as stated above the jacket wasn’t skinned back enough to even make a decent splice, the NEC requires 6 inches of wire extended out of the box. The second thing is wire nuts work if these idiots would tighten them up correctly you wouldn’t have no problem. Your breaker done it’s job, it was tripping because where the splice was made you had one arching which was more than likely arched to the to the neutral. When I splice with wire nuts I get them so tight the wires start twisting up. After that tape up each splice

 

[Lucien Nunes]

When a connection such as a wirenut burns out, it is usually progressive and the resistance rises as the contact surfaces oxidise. It is not uncommon for it to become intermittent before failing completely, misleading you into thinking that changing the breaker had cured the problem. In fact the joint had simply made contact again briefly at the time you installed the new breaker. Hence the value of testing parts of a system for continuity / resistance as I mentioned.

@ Voltstick haters - actually the OP was very close to locating the problem using just the voltstick. Notice his comment and my reply:

Sensor pen tells me there’s still some electricity flowing but not enough for a light.

...with the breaker and oven both switched on and the outlet apparently dead, just check whether it lights on both the hot and neutral of the circuit, because if it does that clearly points to a bad neutral connection...

I read the OP's comment as useful evidence that there was voltage somewhere at the outlet even when the microwave was not working, but that he made the wrong inference from it. My inference was that the neutral was broken, hence my suggestion to double-check that first. A final check that the stick did not light on the neutral within the panel would have very conclusively shown the presence of a failed joint in the neutral between panel and outlet.