Microwave tripping an arc fault on a separate circuit

[Tetra]

Wondering if anyone can help me solve this little mystery...

I have a client who recently bought a new panasonic microwave. After using it for about a week she noticed the bedroom circuit tripped occasionally. The bedroom circuit that is tripping is fed from an arc fault breaker, and it is on a completely separate circuit then the microwave. At first I figured it was simply coincidence but after about 50 trips now it has only ever tripped while the microwave was running (I witnessed this myself). Although the breaker doesn't always trip while the microwave is running, only occasionally. And the circuit the microwave is on never trips, although it is fed by a regular breaker rather then an arc fault, and is fed off of a GFCI receptacle on the kitchen circuit.

I measured the loads on the line and neutral for both circuits and I see nothing alarming, yet the breaker is still tripping. I thought perhaps there was a shared neutral somewhere and the microwave was sending some noise down the neutral causing a tripped breaker, but as far as I can tell both circuits are isolated from each other, until the panel.

I tested the microwave several times, each time I tested I let the microwave run for a bit, and about 1 out of 5 times it trips the breaker (iow I ran the microwave 5 times and one time the breaker tripped per test). I'm fairly convinced it is the microwave causing this but I just cannot figure out how?

The arc fault breaker is only a few years old, GE breaker. Tests fine. Loads are fine. Any ideas?

 

[LEO2854]

Are the two breakers next to each other?

 

[ActionDave]

Got to rule out all of the standard stuff, witch it sounds like you are trying. The fact that a separate circuit trips is odd, but I have noticed the new style AFCI's have more nusance trips with loads involving electronics.

Did you try plugging in the microwave to the bedroom circuit?

 

[Tetra]

The AFCI that's tripping is #8 and the mircowave circuit is #18.

And no I have not tried the microwave on another circuit. I suppose that'd be a good test, but still leaves the question as to how it was tripping a separate circuit?

 

[don_resqcapt19]

T... but still leaves the question as to how it was tripping a separate circuit?

That is a good question, but I don't think that even the manufacturers could answer it. I don't think anyone, including the design engineers, know all of the details on how an AFCI really functions when installed in a real world envrioment.

 

[handy10]

The AFCI that's tripping is #8 and the mircowave circuit is #18.

And no I have not tried the microwave on another circuit. I suppose that'd be a good test, but still leaves the question as to how it was tripping a separate circuit?

I don't have an answer to the question of how it trips, but I suggest that you try the microwave on two different circuits: one on the same bus bar as the arc fault breaker and one on the other bus.

 

[Tetra]

@don, funny you say that, this is actually only one of a few mysterious problems I've encountered regarding AFCI's lately... Usually I just replace the thing if I can't find any real problems but considering the price of these things that's not a very desirable solution. Not to mention this one is actually pretty new.

@handy I think I'll give that a try... atm it's on a seperate bus but I think I will try the same bus simply to see what happens. Being it's an occasional problem and not a constant one though it may not give very trustworthy results.

Has anyone herd of or know of a way to filter the neutrals to these arc faults (without disrupting their arc fault interrupting capabilities)? I'm not an electrical engineer or anything but I have a hunch (and that's all it is) that these issues have something to do with the neutrals picking up noise and messing with the afci's sensitive parts...

 

[hurk27]

with my small experience with AFC's back around 2002 and of a short duration before our state pulled the plug on having to install them I noticed the problem of neusent tripping very simulate to the problem we had with older generation of GFCI's and some that are now coming in from China that dont not include the delayed trip that was built in the GFCI chip of the newer GFCI's

If this AFCI has the GFP function then I would bet you are getting inductive kick back from the transformer in the microwave, one question? is it right when the microwave kicks off as to when the AFCI trips, as this is the indicator of this type of problem as it is never when your running the inductive load or turning it on, but only when it is turned off, back then one of the problems we had was ceiling fans in the bedroom, fluorescent lights in the bathroom, and even the bath fan or even a vacuum cleaner, I played around with some MOV to see if I could get the problem to stop and I found placing the MOV across the switch that switched the inductive load was the only thing that would reduce the tripping, this also worked for GFCI's that were susceptible to neusent tripping, but this would be hard to do with a microwave since the switch is not available and not being qualified to modify one is a risk that no one should take, maybe a newer generation GE AFCI breaker would help with this problem, about the only fix I could see working.

 

[Tetra]

Every time I witnessed the breaker trip it was right in the middle of the microwaves run... One test that comes to mind I ran the microwave set for 5 minutes, and at about 2:30 is when the breaker tripped. According to my client it's the same case every time, right in the middle of the run.

But this microwave is brand new and fairly high tech, hard to say what the transformer, or even the magnetron are actually doing in the middle of the run.

I moved the breaker for the microwave down a slot, and even moved the neutrals on the neutral bar today (the neutrals for both circuits happened to be right next to each other on the neutral bar) gonna wait and see if that helps at all...

 

[don_resqcapt19]

...and some that are now coming in from China that dont not include the delayed trip that was built in the GFCI chip of the newer GFCI's ...

What delayed trip? As far as I know the UL standard has required the time to trip (in seconds) for a GFCI to be no more than:
"the quantity (20/fault current in milliamps) raised to the 1.43 power"

 

[unytko]

Is it just me or more of you have problems with GE AFCI breakers? After my last very annoying situation with simular problem (vacuum and iron) I switched to C H /eton and have no problems since. AHJ acepted them in GE panel after hearing what we went through with client. :thumbsup:

 

[chris1971]

Try a surge supressor on the microwave.

 

[ELA]

To be more specific try an EMI filter on the Microwave. It is less likely transient spikes but rather higher frequency currents that are affecting the AFCI.
A surge suppressor alone will not stop those currents, it requires an EMI filter.

You might do a search here for AFCI + EMI filter

 

[don_resqcapt19]

To be more specific try an EMI filter on the Microwave. It is less likely transient spikes but rather higher frequency currents that are affecting the AFCI.
A surge suppressor alone will not stop those currents, it requires an EMI filter.

You might do a search here for AFCI + EMI filter

Why should the end user have to modify his equipment to make the AFCI work correctly?

 

[Dennis Alwon]

Is it just me or more of you have problems with GE AFCI breakers? After my last very annoying situation with simular problem (vacuum and iron) I switched to C H /eton and have no problems since. AHJ acepted them in GE panel after hearing what we went through with client. :thumbsup:

If you think CH is immuned you are in for a surprise. I have used GE since the advent of the afci and before and until recently-- on one home I have been trouble free. I have replaced a few CH AFCI

To the OP call the manufacturer and see if they can give you an older generation AFCI. GE will send them overnight for free- no cost for the breaker either. CH also guarantees their AFCI for life.

 

[Dennis Alwon]

The problem with the microwave and the bedroom is probably caused because the wires are running parallel to each other and the noise from the microwave is getting into the afci circuit through EMI.

I just heard a story from a ge Tech guy who said he had a customer swear that the afci in the bedroom would trip on every 2nd flush of the toilet. Apparently there was a VFD pump on the system and that would kick in on the second flush. VFD are terrible for afci's.

 

[ELA]

Why should the end user have to modify his equipment to make the AFCI work correctly?

They should not. Someone has to resolve the issue though. Probably a little more difficult to get the AFCI manufacturer and the NEC to change?

 

[kwired]

Why should the end user have to modify his equipment to make the AFCI work correctly?

They should not. Someone has to resolve the issue though. Probably a little more difficult to get the AFCI manufacturer and the NEC to change?

Close enough to my answer.

The problem with the microwave and the bedroom is probably caused because the wires are running parallel to each other and the noise from the microwave is getting into the afci circuit through EMI.

I just heard a story from a ge Tech guy who said he had a customer swear that the afci in the bedroom would trip on every 2nd flush of the toilet. Apparently there was a VFD pump on the system and that would kick in on the second flush. VFD are terrible for afci's.

Anything induced on the circuit is possible trouble with these devices. Next we will have to use steel raceways or metal sheathed cables for all AFCI protected circuits.

Been said before - the consumers are the test lab for these AFCI's - and the tests are far from done yet. Us installers and service techs are just the fool stuck in between.

 

[OhioSparky28]

Possible solution: I had a similar problem with CH breakers.

Possible solution: I had a similar problem with CH breakers.

Customer had treadmill on dedicated gfci outlet and when she ran it, it would trip other arc fault circuits. Cutler Hammer recommended moving tail from arc fault tripping away from neutral of gfci outlet homerun. This did not remedy problem. Second they recommended that I use a CH breaker that was made to work with appliances. I believe the part number is CH120AFA. The neutral tail has a small black patch on it. I replaced the troublesome breaker with the new one and the treadmill tripped other circuits, so I ended up replacing all the arc faults in the panel and have not had a call back for this item. Also note that the microwave is making a noise that the breaker does not like and is likely causing the problem. Hope this helps.

Wondering if anyone can help me solve this little mystery...

I have a client who recently bought a new panasonic microwave. After using it for about a week she noticed the bedroom circuit tripped occasionally. The bedroom circuit that is tripping is fed from an arc fault breaker, and it is on a completely separate circuit then the microwave. At first I figured it was simply coincidence but after about 50 trips now it has only ever tripped while the microwave was running (I witnessed this myself). Although the breaker doesn't always trip while the microwave is running, only occasionally. And the circuit the microwave is on never trips, although it is fed by a regular breaker rather then an arc fault, and is fed off of a GFCI receptacle on the kitchen circuit.

I measured the loads on the line and neutral for both circuits and I see nothing alarming, yet the breaker is still tripping. I thought perhaps there was a shared neutral somewhere and the microwave was sending some noise down the neutral causing a tripped breaker, but as far as I can tell both circuits are isolated from each other, until the panel.

I tested the microwave several times, each time I tested I let the microwave run for a bit, and about 1 out of 5 times it trips the breaker (iow I ran the microwave 5 times and one time the breaker tripped per test). I'm fairly convinced it is the microwave causing this but I just cannot figure out how?

The arc fault breaker is only a few years old, GE breaker. Tests fine. Loads are fine. Any ideas?

 

[ronaldrc]

Why should the end user have to modify his equipment to make the AFCI work correctly?

Hello Don

I started a thread on this very subject a few years back on, why wouldn't arcs on the line side of a AFC
breaker trip it?

You had the correct answer you said the arc signiture wave form had to be several amps. I accepted that answer and still do.

But what if one of my recpts. on an other circuit has a arc and the afc on another circuit trips?
The way I look at it that is a plus it might have save my house from burning down because I called an Electrician
to trouble shoot it.