House electrical problem.

[Don Farr]

I am almost ashamed to ask this considering the field I work in, which is industrial electronics. I am not a licensed electrical but a troubleshooter.
Heck, I go behind the electricians and find their mistakes, but this is a stumper and LOML is really getting irritated with it.
Our home is about 2 1/2 years old and this problem has been there ever since it was newly built and I can't find it.
There a 20 amp breaker that feeds three outlets in the kitchen. Of those outlets, one is almost never used and one has the coffee pot plugged into it and the other the microwave (that one is a ground fault).
About every fifth time you hit start on the microwave it will trip the 20 amp breaker (not the ground fault).
The breaker panel is out in the garage, so you have to go out to the garage and reset it.
I have changed the breaker out, the ground fault receptacle and even replaced the microwave and it is still tripping.
There is a different sound from the microwave when it trips, almost like a bump! or surge.
You guys have never let me down, tell me what is wrong with this circuit. :confused:
Oh, one other thing. I have tried unpluging the coffee pot to see if that that any effect, you know, both on at once. NOT!

[Brad Schafer]

are the other 2 receptacles daisy chained from the GFR? have you inspected/replaced the non-GFR receptacles?

are you sure there is no other load on this circuit (garbage disposal, instant-hot, etc.)?


b

[Chuck Wintle]

What if you try the microwave in the non GFI outlet? I assume the GFI is the type that is the outlet? Maybe remove the GFI altogether and see what happens.

[Chuck Wintle]

When they wire the kitchen outlets is it 1 breaker for 3 duplex outlets. What does the electrical code say for your area?

[Wes Bischel]

Don,
I'm with Brad on this one. Sounds like there is something else on the circuit. It could be something like the furnace for all you know! I guess it's time to put your trouble shooter hat on and figure out what the electrician did wrong versus attempting to ID the faulty components.

Good Luck,
Wes

It could be the refridgerator - though a 20 amp shouldn't go unless it's pulling too many amps at start.

[Don Farr]

are the other 2 breakers daisy chained from the GFR? have you inspected/replaced the non-GFR receptacles?

are you sure there is no other load on this circuit (garbage disposal, instant-hot, etc.)?


b

Brad I'm not sure what you are asking about the daisy chain. The one 20 amp circuit comes into the bottom of the GFR and out of the top it feeds the other two non-GFR's.
I have not changed the two non-GFR's. I thought with nothing plugged into them it was not relevant. They are downstream, so to speak.

[Don Farr]

Sorry, I left something out. They keep bugging me here at work.

No garbage disposal or hot water. The dishwasher may be on that circiut but we never use it. I guess I need to check into that.

[Don Farr]

What if you try the microwave in the non GFI outlet? I assume the GFI is the type that is the outlet? Maybe remove the GFI altogether and see what happens.
Charles it is a ground fault outlet with the test/reset buttons on the front. I replaced it but I can slid the microwave down and try a non-GFR just to see what happens.
It is an intermittent problem and has been known to go away for a day or two.

[Lee Schierer]

If there are three outlets in the ktichen on the same circuit, I bet there is a fourth. Go throw the breaker and see if the fridge light comes on when you opne the door. If so your kitchen was wired by the same guy that did mine.

:D

[Jim Becker]

Test for an open neutral...I just had an old circuit get flaky and that was the problem. Unfortunately for me, I have to have a new circuit pulled up to the MBR and bath...the problem area is inaccessable.

But barring something weird like that, I also suspect you have something else on that circuit that is occasionally contending with your microwave. While the two kitchen appliance circuits required by code are supposed to be dedicated...shortcuts could have been taken. "Something" is pulling amperage when the breaker is sprung. BTW, that situation would not cause a GFCI to pop...it reacts to different circumstances, not amperage load.

[Brad Schafer]

The one 20 amp circuit comes into the bottom of the GFR and out of the top it feeds the other two non-GFR's.


Don, that's what I was after. Apologies for poor clarity on my part.
BTW - a GFCI basically measures flow from hot to neutral. If there's more than a few milliamps imbalance, it trips. This might be something as simple as poor ground wire routing inside a box.

First thing I'd do is open up the two (known) receptacles and check them out. Make sure they're in good shape and that the ground wire is securely fastened and routed correctly (read: not up against a neutral).

As other posts have suggested, I'd then plug the uwave into one of the other receptacles. If same thing happens, I'd shut the circuit down again and find the "4th" (or 5th) box. :D

Good luck,


b

[Kevin Gerstenecker]

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! :D
(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!)

[Dennis Peacock]

Don,

As an Ex-Electrician that has had his share of circuit troubleshooting, here is what I did and still do when I experience a weird problem like this:

1. Purchase a 9 volt (large lantern battery)
2. Purchase a bell or buzzer that will operate on that voltage.
3. Disconnect the HOT (black) wire and the Neutral (white) wire and wire the bell/buzzer and battery to those two wires.
4. Unplug the microwave from the circuit.

With everything unplugged from the suspect circuit the bell should NOT ring. Take a plug and wire the two prongs together so that you can plug it in a "dead" recepticle that only has the battery/bell wired up to it. The bell will ring loudly when the circuit is completed.

With everything unplugged from the suspect circuit and the bell "buzzes" or rings softly, there is something else in the circuit that is drawing current and completing enough of the circuit to make the bell ring enough to be heard when close to the bell.

WARNING!!!! Only perform this test on recepticles that have been PROVEN to have no A/C power applied to them or you will really see fireworks!!!!!!

The above proceedure is one that I have used literally 100's of times. The low ringing will be an indication that a motor of some type in trying to run on the 9 Volt circuit. If this is the case, you need to look further into the circuit. Here, electrical code requires that the kitchen outlets be split across two seperate 20 Amp circuits.

You don't have to follow my advice, just an idea to help better troubleshoot and maybe resolve your problem with LOW VOLTAGE. :)

[Don Farr]

Well, upon further investigation I found a fourth outlet on the end of one of the cabinets. Unfortunately we never use that outlet either. I guess this weekend when I have time I will remove all the covers and inspect the outlets. Dennis I have a megger that I think I can do the same thing with that you are describing. Just measuring leakage to other circuits if I understand you correctly.
Kevin, I also like your idea about moving it to a different breaker. My well pump is next to that breaker and I have had some unexplained dealings with that.
thanks to all, you give me lots of things to check and try.

Oh Lee, the fridge or dishwasher is not on that circuit.

[Joe Breid]

Don,
A number of years ago I had the same problem that you are describing. The microwave would trip the breaker when it was first turned on. This happened intermitantly, sometimes more than once in a day and at others, several weeks apart. I never did find a cause other than the problem went away when we got a different microwave. Apparently, there was a high current draw at times when the microwave was first turned on.

Joe

[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! :D
(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 :confused: 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. :D 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? :confused:

[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.