House electrical problem.

[Don Farr]

Don, what I would do first is check the Amp Draw on the Circuit in question. Take the cover off the panel, and locate the hot wire on the breaker. Clamp the Amp Clamp Meter around the Hot Wire, and check the Amperage reading on the Meter, with the Microwave off. With the meter still clamped around the hot lead just beyond the breaker lug, have someone turn on the Microwave to the full power setting, and again check the Amp Draw. If it is a 20 breaker, you don't want to draw more than 80% of the 20 Amp rating, or 18 Amps. It the load on that circuit is drawing near or over 18 amps, there has to be another significant load on that circuit. It could be that you have a weak breaker that trips before it approaches the rated load limit, in this case, 20 Amps. If you find a safe amp draw on the circuit, I would replace the breaker, or swap the hot wire with another breaker above or below the suspect breaker in the panel, and see what happens after a few days. It just doesn't sound to me like a wiring problem...............it appears more like a loading or breaker problem. Good Luck, and be careful with those Electrons.............they can have an attitude at times!
(During all of this, don't rule out the appliance itself........they have been know to make you pull your hair out looking for a secondary problem that doesn't exist!)

Kevin, what a novel idea. Check the current on the circuit. Duh I must have missed that last night because I got those little hot sparky things in my eye. Sometimes I try to over complicate things. I will take a clamp-on home tonight and check it. I also have a 7 day recorder if needed. Thanks.

[Steven Wilson]

Don,

I would also look at your garage outlet and any outside outlets. My house was new in '96 and the circuits that have GFCI are strange. I have one kitchen circuit that's ok, the other is also tied with an outside circuit, my other outside circuit is tied in with the garage recepticle. The newer houses have a more sensible arrangement but the ones from the late 90's are weird.

[Don Farr]

I am not sure what order these will come up but one is my handy dandy outlet tester (circuit OK), microwave off, microwave on, and most interesting is the peak current when MW is turned on. Kevin, correct me if I'm wrong but that is getting very close to 125% which is tripping current for most breakers.

[Kevin Gerstenecker]

WHOA! There is a problem with that Circuit Don. I can't quite make out the setting on the meter..................but I CAN make out the reading and a tick over 24 amps on a 20 amp circuit is NOT a good thing. I don't need to tell you that Don, as your experience with Electrical Circuits has already done so. If that reading is with the Microwave turned on, then the Microwave oven has a problem. I have personally never seen a Microwave draw that kind of Current...............even the "Binford 5000" Microwaves draw under 20 Amps. The most unsafe thing about that current amperage situation is what can happen in the event of a "Hanging" Breaker. There have been instances where a Circuit Breaker will hang, and not trip, and this is what causes fires. The Breaker is there to protect the conductor from overheating due to overloading, and a breaker that does not trip = FIRE. What I would do just to be sure, and conduct a little experiment of sorts is to take the Microwave to another Circuit in the house that you have Amp Clamped and found to be drawing almost nothing........like a Bedroom perhaps. Amp Clamp the conductor for that Circuit and take a reading.........then plug in the Microwave and turn it on.............if the Amperage Spikes, the culprit is the Oven. This may be overkill...........but it wouldn't hurt to double check just to be sure you didn't miss another load on the circuit currently in question. Whatever the case, you really need to do something to eliminate the problem that you found............that is NOT good! Let me know how things work out, but I think you have found the problem...........actually Don, this was an easy one, although it is a bummer that the Oven may be shot.

[Brad Schafer]

don, i'm with kev on this one. 24A peak and 13 sustained, if i read every correctly (which i don't always do). that's WAY up there. dang.

looks like the nuker is nuked,


b

[Don Farr]

I understand what you guys are saying, but just a month ago I trashed my old MW which was a 1200 watt unit and down graded to a 1000 watt unit. Do I need to find one that draws even less current?

[Chuck Wintle]

This may be a dumb question but did you measure the voltage at the outlet? We had a compressor a work that would stall often and it was because the voltage was low at the plug

[John Christiansen]

I am not sure what order these will come up but one is my handy dandy outlet tester (circuit OK), microwave off, microwave on, and most interesting is the peak current when MW is turned on. Kevin, correct me if I'm wrong but that is getting very close to 125% which is tripping current for most breakers.

Well this has been interesting, and now that you've clamped the circuit it is explained what is causing your trip. But....... how long is that 24 amp spike holding. a good circuit breaker should be able to hold a small overdraw like that for quite awhile before tripping. It's expected. Many pieces of equipment draw well over their run amps on startup. If every breaker tripped the instant they saw an overdraw it would be quite a nuisance. Which is what you are dealing with here.

Example: Just recently I had to deal with a tripping breaker in a walk light circuit on campus. 30 amp Square D breaker. When the lights were turned on I was drawing 38 amps for at least ten minutes before the breaker would finally go. It took me two days of digging to find the problem but we are now back to drawing 5amps just like it should be.

Try Kevins approach, wire into another breaker or take the micro into another room and track that some. If it spikes to 24amps and holds it long enough to trip a different breaker then I guess you've got a problem with your micro. If it spikes to 24amps and then drops back without tripping the new breaker after several tries, then, replace the old breaker.

[Don Farr]

Charles I did monitor the voltage at the outlet for about 1/2 day. It stayed around 120 VAC +/- 2 volts.

John I probably did not explain my photos well enough last night. You can't even see that 24 amp inrush unless you use the peak hold fuction on the clamp-on. They claim that it will catch a 1 ms peak, so that 24 amp inrush is there for only an instant.

Thinking about this in light of day, the numbers don't work out.
P=I x E. 13 X 120=1560 watts. I think when I get home tonight I will check the nameplate on the microwave and see what it says for ratings.

[Ron Meadows]

Don,

P=VI won't work very well to determine the Watts put out by your microwave. A microwave converts low frequency (60 Hz) to something a little over 4 GHz to heat your food. There is an inefficiency in this conversion that can make for the numbers you are seeing.

GFCI circuits and microwave ovens usually don't play well together on devices with very large inrush currents. Is there anyway for you to put a regular outlet in the receptacle that you plug the microwave into and move the GFCI to the next outlet downstream??

hope you get this figured out,


Ron

[Craig Honeysett]

Don, Just a suggestion, but you have too many options to consider so first thing you need to do is move the microwave to another circuit and see if it trips that breaker. That way you can eliminate the device as the culprit. If that checks ok then without the microwave running as someone suggested measure the current draw on the circuit. If that checks OK you are now down to physically inspecting the components.