I have a Kenmore (over the oven) Microwave Oven, Model #721.81623600 that, whenever we use it, the power fluxuates.
The lights, LCD and fan dims on the unit then regains it's full power again then everything dims and slows down again. This senario continues the whole time the microwave is running.
The units on it's own 20 Amp circuit breaker so I know there's no other draw on it's current.
I'm trying to figure out if it's the microwave or the circuit breaker itself. Does anyone have any ideas to help me determine how to this problem?
The units built in 2006 and was pretty expensive as microwaves go. Of course the 1 year warranty from Kenmore has expired. Just my luck.

Unfortunately, it could be either a loose connection (outlet, wiring, bad breaker or the microwave.

Measuring the voltage at the microwave/microwave outlet would be the first order of business.

Measuring the current drawn with a clamp ammeter would be the second order.

That would determine if it's microwave or wiring.

The High voltage capacitor or magnatron would be my first suspect.

I used a meter at the outlet and it was 123-130Volts. I plugged the microwave into another outlet via an extension cord and it worked fine. No power fluxuations. I replaced the ciruit breaker and it is working fine now. Whew... I thought it was going to be a problem with the $500.00 plus microwave. Problem solved with a $4.00 circuit breaker. Thanks for your input.

Glad it worked out. I'll have to remember the extension cord trick.

FWIW: You could have measured the voltage across the terminals of the breaker while the microwave was on, but his is a difficult measurement to do. A large voltage across the breaker when it's closed indicates a contact resistance problem.

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Originally Posted by KeepItSimpleStupid

Glad it worked out. I'll have to remember the extension cord trick.

FWIW: You could have measured the voltage across the terminals of the breaker while the microwave was on, but his is a difficult measurement to do. A large voltage across the breaker when it's closed indicates a contact resistance problem.

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My son-in-law did measure the voltage across the terminal of the breaker while I ran the microwave. The Microwave's spec label says it is a 14 AMP unit.
It registered a draw of 14.75 at the circuit breaker terminal when the microwave was running at 100% power.

Nope, that's current. There are error bars on clamp on meters. 3% is typical, so 14.75 vs 14A is no big deal.

The voltage ACROSS the breaker contacts. From the main bus bar to the output terminal should be near 0V. As an example, suppose that the contact resistance was .020 or 20 milliohms, then the voltage would be V=14*.020 or about 28 mV. Now suppose the contact resistance was 1 ohms. The voltage measured would be V = (14)(1) or 14 Volts.

You would then see a little higher than the 14 V drop at the microwave. V = 120-(14 or more) volts.

Thanks so much for your input. I'm just estatic it wasn't the microwave. That puppy cost me too much money to go bad after only 2 yrs.