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I've really got two possibly related issues here. We have a basement office that we wired ourselves. Code required that we put in an AFCI breaker. From what I've read these can be pretty temperamental and that has been the case with us. The breaker will trip as often as once a day but it is usually less often. We replaced the original AFCI breaker and for about a month after we were good. However, now it has started tripping often again.

I have a surge protector hooked up on one outlet with a PC and monitor attached. It is the kind of surge protector with the master outlet that can control the other devices so they turn on/off when the master device turns on/off. I've noticed that anytime we run the garbage disposal upstairs and also at many random times throughout the day, the surge protector will make a clicking sound, like the power has come on/gone off of the main device (the PC). The PC isn't turned on.

Any ideas what might be going on here, both with the breaker flipping and/or the surge protector clicking? I know we have mixed wiring of 15A (14 gauge, white) and 20A (12 gauge, yellow). The AFCI breaker itself is 15A. Could either of those be a possible problem or does it sound like this is something else? Bad outlet(s) along the circuit?

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  • Is the office the only thing on the circuit, or does the circuit supply other rooms too?
    – Tester101
    Mar 15 '11 at 12:28
  • Are there any GFCI receptacles on the circuit?
    – Tester101
    Mar 15 '11 at 16:49
  • The office does have one wall shared with our family room that has the TV, DVR, and a computer plugged in. There are no GFCIs on the circuit. Mar 15 '11 at 18:44
  • How many fixtures (receptacles, lights) are on the circuit? Are unusual items plugged in / running when it trips (vacuum cleaner, circular saw, one particular lamp)?
    – Tester101
    Mar 15 '11 at 19:57
  • I'm not sure how many are exactly on the circuit. I made sure to keep it under 10 per circuit. Nothing unusual plugged in when it trips. Usually it is when I'm on the computer. It has happened with a couple of different computers. It has only happened a couple of times when I was just watching TV. Mar 16 '11 at 14:12
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I've had some issues with AFICs in the past, and one quick thing you should check (which ended up being my problem): Is the insulation on the wire coming into the outlet box pinched and causing a loose/flaky connection? That will still give power to the outlet (under a normal breaker) and won't trip a normal breaker, but it'll drive an AFCI nuts.

Another technique you can try to debug this is by swapping in a GFCI breaker, and see if that trips too. If the GFCI trips, it's a grounding problem. If it only trips on the AFCI, then there's arcing somewhere along the circuit. Check junction boxes, the outlet boxes and the connections to the plugs in the boxes.

Happy & Safe Debugging!

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  • Oddly enough, my breaker hasn't tripped again since the day I posted my question here! Very strange. I looked up the manual for this particular breaker and it has an indicator light (when it trips) that tries to indicate what the real problem is - whether is it load related or an arc fault. However, I haven't been able to check since it hasn't tripped. Thanks for the tips. May 16 '11 at 14:22
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AFCI/GFCI Breaker Diagnostics

Depending on the brand and model of AFCI or GFCI breaker you installed, the breaker itself may be able to help diagnose the problem. For instance, Square D QO Combination Arc Fault (CAFI) breakers have what they call Time Saver Diagnostics. For more information see the Time Saver Diagnostics handout. Below is a summary of the Time Saver Diagnostics steps:

  1. Turn off the circuit breaker.
  2. Hold down the test button.
  3. Turn the circuit breaker back on while holding the test button.
  4. The amount of time it takes the circuit breaker to trip indicates the type of failure:
    • If the breaker trips immediately, it is detected a fault to ground.
    • If the breaker trips after a two second delay, it is detecting an arc fault.
    • If the breaker trips after a five second delay, it is a thermal overload or short circuit. If there is no issue on the circuit to be diagnosed, tripping after a five second delay would also be a normal breaker testing operation.

AFCI General Debugging Steps

Even with diagnostics built into the breaker, solving AFCI nuisance trips can be troublesome. However, they can also reveal latent problems. (They recently helped me determine that my garbage disposal was arcing and sparking whenever it was turned on, even though on a non-AFCI breaker, it had appeared to be working fine.) Part of the problem diagnosing AFCI nuisance trips is that loose wiring connections can appear fine when there is no current load, such as when using an outlet tester, but then be problematic when equipment (e.g., computer, garbage disposal, power tool) starts drawing current load.

Potential Problems

Potential problems include:

  • Bad device plugged into the circuit (e.g., surge protector, computer, etc.).
  • Bad AFCI breaker.
  • Nail/screw through the wiring buried behind the wall.
  • Loose connections, such as in the electrical panel, outlets, or equipment.
  • Pinched/kinked wires.
  • Wires with exposed copper or damaged insulation.
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I wasn't sure what an AFCI was, so I did a quick google search. I came up with this page:

http://www.thecircuitdetective.com/afci_circuit_breakers.htm

which gives lots of info and a detailed procedure for troubleshooting this issue. In particular, it sounds to me like your issue might be the shared ground problem, ground from one circuit mistakenly connected to ground from another circuit. That said, the troubleshooting procedure is rather involved. See the page above, and then decide if you want to attack it yourself or call an electrician. Hope this helps.

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  • 2
    I think you mean a shared "neutral" problem. The ground should be common for all the circuits in the house.
    – RSMoser
    Mar 15 '11 at 17:55
  • I have seen that circuit detective site and it did help a little. I also did a little more digging on our particular AFCI. It is Siemens brand and apparently has an indicator light to help diagnose what is causing the breaker to trip. If there is no light then it means either an overload or a short-circuit. If there is a light it means an arc fault or a ground fault. I'll post here next time it trips with the results. Mar 15 '11 at 18:48
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Your AFCI is behaving as it should.

That clicking you hear in your power strip is a relay clicking. A relay is a mechanical switch activated by a magnetic field. The act of opening an closing the switch will cause an arc. A tiny one, but still an arc. Opening and closing a bunch of times in a row means more arc.

You need to figure out why the power strip clicks. It might be sensitive to under-voltage, and when your disposal is running, it might lower the voltage in your entire house just a bit.

I suggest replacing your power strip with a band-new, no frills type and see if that solves your problem.

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