We have a brand new home in Puget Sound which we moved into 2 months ago. We are plagued with constant, random, tripping of multiple AFCI breakers on a daily basis.

Some days, just two or three breakers will trip. Other days, we’ve had as many as 7, 8, or 9 of the breakers trip throughout the course of the day. Every one of those 19 breakers will trip at one time or another.

The load panel is Square D, and has 19 AFCI breakers on the left side. The only correlation we can make, as far as what activity will trip breakers, is that it only happens when the American Standard TAM9 air handler/heat pump combination runs. If the air handler/heat strip runs, and the heat pump is offline, there will be no tripping.

The builder has put responsibility for resolving this problem at the feet of the electrical contractor and the HVAC contractor.

The electrical contractor, so far, has replaced every AFCI circuit breaker in the panel twice. He has run a new 240v load line from the service panel to the heat pump. The electric utility company has placed recording meters on our outside meter, and the local service distribution point for the past month and has recorded no anomalies.

The electrical contractor has claimed his lines are all good, clean, and solid and says “It must be something with the HVAC installation.”

The HVAC contractor has replaced the entire system, piecemeal over the past month. First it was the heat strip, then it was the heat pump, and this past week, they put in a new air handler, thermostat wire, and thermostat.

The daily, frequent, random tripping of breakers continues, and the HVAC contractor says “It must be something with the electrical installation.”

The SquareD AFCI breakers have a test button that will report the cause of a tripped breaker by pushing in the test button and switching the breaker back to ON. If the breaker switches off after 3 seconds, it’s an arc fault. If it switches off immediately, it’s a ground fault.

Every time I’ve gone through this test process, the breaker responds with an immediate ground fault response. Every time...ground fault.

Last Friday we had two tech’s from American Standard come out, accompanied by the electrical contractor, the HVAC contractor, and the builder. They spent 3 ½ hours testing, looking, and testing some more. At the end, they were all standing outside in a circle, scratching their heads and saying “I’ve never seen this before.”

Meanwhile, my wife and I are at our wits end. My understanding of electrical matters can fit in a thimble, but ground fault, to me, must mean something in the electrical system. I am told that our entire home’s concrete, rebar reinforced foundation IS the earth ground for the home’s electrical system. The footprint the foundation is 70’ X 40’.

Is there such a thing as “too much” earth ground? Could it be that the complexity of all that rebar is creating some kind of ground loop that feeds back to the panel. Could it be that the ultimate path to earth ground is defective?

I don’t know, and the electrical contractor tells me that, as far as his tests can show, there is absolutely no problem with the electrical system.

I would really appreciate any knowledgeable insight on this because, all I have thus far, is watching a circular gunfight between the builder, electrical, HVAC, and American Standard.

So far, they are all shooting blanks.

Thank you, in advance, for any thoughts!

  • 1
    Picture of the panel? Has anyone talked to square d engineering support? Apr 12, 2021 at 5:14
  • Is your panel QO (skinny breakers with the windows) or Homeline (fat breakers, no windows)? Apr 12, 2021 at 11:40
  • I've got a photo of the panel before it got closed-in with drywall...I'll dig it out and post it later...thanks! Apr 12, 2021 at 14:52
  • 2
    Most new homes these days come with some sort of warranty. Even if yours doesn't, there is some implicit expectation that things will work correctly, at least for a time. I would suggest calling the builder to come back to have a look at it and have them sort it out & fix it. If you start messing with things before you call them in, they may decline to work on it, blaming you and your "adjustments" for the problem.
    – FreeMan
    Apr 12, 2021 at 15:18
  • 1
    Are you suuuuure you're sure about the interpretation of Square D's Time Saver Diagnostics and "3 seconds"? Humans are not good at being stopwatches. And your explanation of what the Time Slaver diagnostics mean does not match my recall. Apr 12, 2021 at 17:44

5 Answers 5


Your grounds are certainly not the problem. More grounding is better, and an Ufer ground tied into the foundation is the best there is.

19 AFCI breakers, eh? And people wonder why we say "Go BIG" when buying service panels. They're all on the left side, but that doesn't indicate anything special - for instance they're not all on the same "leg". If every other row of breakers was tripping and not the others, that would be interesting, but I'm sure you would have mentioned that.

A marvel of compact tech

A semi-modern "AFCI" breaker has 3 detection modes of interest to us today.

  • Overcurrent -- you are pulling significantly more than 20 amps (which itself has 2 modes, but that's irrelevant here).
  • Arc Fault - a small computer with a digital signal processor is listening to the electric line, for that characteristic sound of arcing - that "crinkle crunch" sound you get when plugging in headphones, or headphones with a bad connection, or hooking up speakers with the amplifier turned on. This is listening for series arc faults (inline with the load on hot or neutral), or a parallel (shorting) arc fault between hot and neutral.
  • Ground fault - this is a weakened form of "GFCI", closer to a "GFPE" or a European "RCD". Not good enough for human safety, but an effective way to detect parallel (shorting) arc faults hot-ground or neutral-ground, e.g. a hot wire sparking to a ground wire. Those are also ground faults.

Square D's "TIME SAVER Diagnostics", available on breakers with a white or purple TEST button, will store the cause of the last trip: immediate trip means a ground-fault (meaning the AFCI's weak GFCI-section detected a hot-ground or neutral-ground fault). A 2-second delayed trip means the computer detected the "sounds on the wire" of an arc fault. A 5-second delay means, well, the ground- and arc-fault sections don't know why it tripped, so it must be the dumb old overcurrent breaker.

In the panel, everyone can hear you scream

The nature of the overcurrent and ground-fault tripping means that they can only trip for problems on the "Load" side of the device.

However, the "computer, listening" has a side-effect: It's listening to the "Load" side of the breaker, but the circuit breaker has very low impedance across it, and no noise filtering. As such, the computer can "hear" arc faults on the "Line" side of the breaker, i.e. the panel's main bus. An AFCI trip can occur from other circuits having an arc fault.

It's probably one thing

And I think that's exactly what's happening to you. One of your circuits is arc-faulting, and the other circuits are "hearing it" sufficiently to trip them.

It sounds like you can guess which circuit that is.

So where do we look for arc faults on a particular circuit? Start at terminations of wires - breaker lugs, terminal screws, wire nuts - any end of any wire can be the source of the problem. I would say replacing all the heat pump components is an expensive way to re-torque connections... but suffice it to say, any connections disturbed by this overhaul can be excluded since they've been re-torqued.

So I would focus on the connections which were not disturbed by that recent work, e.g. those on the breaker or neutral bar, or any intermediate splices.

It could be in the machine, but if the machine has been replaced, that would be surprising.

The last and remotest possibility is a broken wire - again typically that is near a termination, but it's not common at all. It could also be a nail driven into a cable.

  • @GregHill I can't edit comments either after 5 minutes. Apr 12, 2021 at 22:43
  • @SteveSether yes, absolutely! Your logic is superb. Apr 13, 2021 at 16:08
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    I once had a friend ask me to check out a light switch that was buzzing for the fluorescent in his stairwell. I asked him "The fluorescent is buzzing?" thinking of ballast problems and he said no the switch. So I drop by expecting to find some failing electronic device, but it was a garden variety 3-way switch that someone had wrapped a wire around the screw but not done it up. It arced continually while the light was on. If the AFCI breakers can sense other circuit over the main bus OP may need to check termination everywhere. Good to know how AFCIs work thank you.
    – K H
    Apr 14, 2021 at 6:32

Ground faults in the wiring are easy to test for.

Most residential only electricians don’t have to verify the insulation so yours may not have this tool or experience but if he also does industrial most likely will have a megger or a high voltage ohm meter is used to test the wiring.

Both the breakers and load devices should be turned off to preform this test and both the hot and neutral should be tested to ground at 500v if not 1000v.

This simple test proves the wiring is good beyond peak values.

the combinations of the loads may be creating harmonics. AFCI breakers can not tell the difference between many harmonics, and even motor arcing from a real arc so they trip for safety.

With the latest and greatest electronic controls added to electronic lighting it may be the harmonics generated by the solid state controls on the hvac system or other devices in total causing the faults.

7,8,9 is a lot of breakers I have seen Refridgeration, mini splits, electronic controlled stoves and several induction stove tops cause these problems along with washing machines and vacuum cleaners many times a direct cause and effect can be identified, dim the lights in the theater/ family room and the breaker trips or a heavy base pulse on the surround sound all can be caused by harmonics.

Random tripping on so many different breakers might be from a heavy load in combination but I would identify every circuit that has tripped and first Meg them to verify the wire insulation integrity. It could be backstabs or real problems with loose connections, but my experience had been more harmonics driven tripping.

Oregon allows for electronic protection to not be used in cases with known problems I would want to check those possibilities first or prior to going to a standard breaker in the problem areas if allowed by your AHJ.


I've heard of AFCI breakers tripping due to nearby ham radio operations. In a video of the phenomenon, breakers would begin to trip at random, often several in rapid succession when the radio was turned to particular frequencies and power levels. If I'm not mistaken, these were Square D devices as well.

  • 2
    Interesting as this is, it's more of a comment than an answer. You might consider revising it.
    – gnicko
    Apr 29, 2022 at 23:37

This is tricky because the breaker is apparently indicating ground fault, but the symptoms (random tripping of all breakers, but only while the heat pump runs) don't seem like a great fit for a ground fault kind of problem.

I have learned by experience that leakage between neutral and ground, even when there's no load at all connected to the corresponding hot wire, can trip the GFCI which monitors that neutral. Clearly that's not exactly what's happening here since arbitrary breakers are tripping. I don't know whether it's technically possible that a single ground fault can cause an arbitrary breaker to trip or not. If the neutrals from two or more circuits were tied together somehow that would surely cause strange results, but again I'd expect trouble only from the breakers involved with those specific circuits.

That said, Ed's suggestion of high-voltage testing for ground faults costs only a couple hours of labor from the right electrician. It could help eliminate ground fault as a possible cause -- maybe the diagnostic from the breakers is wrong somehow. I'd suggest doing the same test to look for leakage between neutrals of different circuits too. More specifically, I'm thinking of lifting the neutral off the first breaker, test for leakage from that back to the neutral bus, reconnect to the first breaker. Repeat for each additional breaker.

Apart from the electric utility service does the house have a connection to other electrical networks -- cable TV/internet, for example? You could test disconnecting that for a day.

Now switching over to the possibility of actual arc faults and/or nuisance harmonics.. You mentioned that the branch circuit breakers have all been replaced and the cable to the heat pump as well. If the heat pump has a pull-out type disconnect switch has that also been replaced? Have all connections on the service from the utility into the meter panel (and the feeder cable from there to sub-panel, if applicable) been re-torqued or even cleaned and re-made? Check for any loose bolts or less-than-pristine clean connections on the buss bars in the panel(s)?

  • I'm really grateful for all the input and ideas here and am passing all this on to my builder (Titan Homes NW), Electrician, and the HVAC people. Still looking for ideas on how to solve this, so please let me know if I can add any information that might be helpful to keep your ideas coming. Apr 15, 2021 at 1:09
  • We've had some beautiful weather here in Puget Sound the last couple of days, so the heat pump has not been called into service at all. As a result, we've had no breakers tripping...at all. Today, with Windows closed, the inside temp at the t-stat reached 78 degrees. I set cooling to 76, and within 15 minutes 4 distinct circuits tripped. So: call for heat, or call for cooling, either will trip random breakers. Apr 19, 2021 at 2:49
  • Neutral-ground faults can cause all sorts of unexpected problems. They allow some of the current that should go back to the breaker panel on the neutral to leak back through the grounding wires instead. This leakage may only only produce enough current to trip the breaker when there is a large load switched on.
    – Simon B
    Apr 16, 2022 at 11:41

Have you gotten a resolution on this? I worked on an main electrical Panel set up years ago that had quite a few engineers scratching their heads. Issue was a main switch (GFI protected) would trip randomly, this went on for weeks. In most commercial builds it's a requirement to do a Ufer ground, and also a second ground outside, and test them. This build also had 2 Ufer's because of the size of the building and multiple wings. Well it turned out that the Ufer's were creating a loop that the Breaker would see and trip on. I would suggest asking the electrical contractor is there are multiple ground wire connections.

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