2

My second-hand 1300 W microwave oven worked fine for years, but a few weeks ago, while running, it blew a fuse (with nothing else turned on on the same circuit). Landlord replaced it, I tried the microwave again, and it worked fine.

Continued using it normally for a few weeks, and then yesterday while running it, sparks and burning smell came out of the back, presumably from the outlet itself, since I don't see burn marks anywhere else, and plug is slightly melted.

Is this just because the outlet is old and not making good contact with the prongs, causing arcs when high current is flowing and the connection breaks? (But why would that blow a fuse?) Or could there be something wrong with the microwave itself?

Edit:

I replaced the melty plug, connected it to a different outlet with a Kill-A-Watt in between, and cautiously tried to heat some water. The microwave sounded a little weird, and the current ramped up to 16.7 A and the Kill-A-Watt started beeping.

Soooo I guess it's time for a new microwave.

Edit:

The brand-new microwave also draws 16.7 A, voltage drooping to 114 VAC. 😒

Similar discussion: "Panasonic inverter microwave drawing more current than it should"

I found manuals for both, and they say:

The oven must be plugged into at least a 20 A, 120 V, 60 Hz GROUNDED OUTLET.

I don't understand how they are allowed to use a 15 A plug for a device that draws 16.7 A, while claiming it requires a 20 A outlet. Shouldn't they be required to use a 20 A plug? Maybe because the power level is selectable?

This FCC document says

7. EQUIPMENT SPECIFICATIONS:
Electrical Power Requirement: 120V, 60Hz, 12.7A

REPORT OF MEASUREMENTS
Supply Voltage: 120 Volts, 60Hz, 16.7A

But I guess the FCC only cares about emissions, not power draw.

3

You will have to do some troubleshooting but I would not use that outlet again until it is replaced/fixed. You have basically 3 possible issues.

  1. Microwave is having an issue and drawing more voltage during a certain phase causing circuit/outlet to be overloaded. I had a microwave in college that fried 3 outlets before I realized... maybe I don't plug this thing in anymore (and maybe that is why some dorms don't allow microwaves in rooms.

  2. You have a bad outlet or connections at the outlet level.

  3. The circuit you are running this one isn't big enough to handle it or you have introduced other things on the circuit (could just take a couple lights) to overload it.

The problem is the fuse should have blew again before the outlet was fried - I really hope the landlord didn't just replace the breaker to a larger size so it didn't trip. If you are in a jam where this is really the only outlet you can plug the microwave into I would suggest a first step is replace the outlet with a GFCI.

5
  • 1
    All good, except that a GFCI will not protect against a pure overload because if hot == neutral then GFCI is happy, even if 25A instead of 12A. Jun 28 at 19:39
  • 1
    @manassehkatz-Moving2Codidact - yea I know and should have explained it. I just suggested in case there were issues with micro and really to just make sure there is a good outlet.
    – DMoore
    Jun 29 at 6:27
  • I tested with a new plug and the microwave drew over 16 A, so that's why the fuse blew and that's why the plug melted.
    – endolith
    Jul 3 at 0:49
  • I added more details to the question
    – endolith
    Jul 5 at 14:06
  • 1
    @endolith - this sounds right. There is nothing you can do other than plug this into a different circuit. I had an old home with a 15A circuit for micro... Had two wall lights on circuit. Micro drew ~14A and lights would trip breaker. The weird thing is... the actual circuit failed. Somewhere in the last 8 feet the wire stopped conducting and I just swapped everything out for larger 12gauge... Point is if drawing too much can actually cause a wire to fail over time it will continuously fry outlets that arent up to spec.
    – DMoore
    Jul 5 at 19:06
3

This is a problem I regularly see with builders grade receptacles the 99 cent ones that landlords & cheap builders love to use.

I would not mention that it was a used microwave, it was working fine. Microwaves are a fairly large electrical load for a receptacle much like a plug in electric heater drawing 1000-1500 watts.

The cheap or “inexpensive” receptacles loosen up creating more heat and with a bad connection the arcing and sparking.

If the plug is damaged I would install a new one and verify the microwave still works on another receptacle then ask the landlord to replace that receptacle.

Builders grade receptacles in the rentals I supported had a 3-5 year life another contributor to this site had up to 10 years in his rentals. I convinced the owner to use specification grade receptacles 3-5$ and they never fail. Is it worth it to pay an electrician to put a 1$ receptacle in 3 different times let’s say at 50$ per install, 153$ over 15 years, or spend 5$ on one and it will last 15+ years cost 55$ simple math says the better receptacles are worth it.

I mention having an electrician do this because in many states it requires a electrician or a licensed handyman with a restricted electrical license to do work in rentals or commercial property.

2
  • True on the outlets... There are A LOT of apartments that don't meet current electrical code and he could easily have a 15 AMP circuit for that microwave that has another outlet and two lights on it.
    – DMoore
    Jun 28 at 18:34
  • @DMoore When the fuse blew the only other things on it were a small lamp, so I don't think that's it. It's a 1300 W microwave = 11 A
    – endolith
    Jun 28 at 18:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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