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I have an AFCI Breaker that trips with 0 load - nothing plugged in, no lights on. To test that power is getting to the room, I turn on the overhead CFL lights (very light load) and flip the breaker. The lights do turn on, then the breaker trips and power is shut off.

When I replace the AFCI Breaker (15A) with a standard breaker (15A, I have both in my panel), the standard breaker does NOT trip. However, no power flows to the room either - no lights, and no outlet power.

What could be causing this discrepancy? I have confirmed that the AFCI Breaker and the standard breaker work on other circuits; they are not faulty.

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migrated from electronics.stackexchange.com Sep 6 '13 at 15:52

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CFL lights PSU is probably very capacitive and it's the size of the PSU that determines the in rush current not the CFL lights that are on. So my speculation is the AFCI is seeing the inrush current as an arc it needs to interupt. Can you turn off the lights and then turn them on once the AFCI has been turned on? Or does that trip the AFCI as well? (Sometimes it helps) It's bassicly what James Cameron said .. oops –  Spoon Sep 6 '13 at 11:24
    
Low load (CFL lights) is not the same as no load. –  BMitch Sep 23 '13 at 12:12

4 Answers 4

Given that you state that "no power flows to the room" when you use a normal breaker, the most likely explanation is either that there is a short/arc somewhere, or the wiring is incorrect.

Shorts/arcs are not something to be messing around with. I would call in a professional.

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Wild speculation follows:

  • the CFL lights in conjunction with the wiring and the AFCI, are causing a false positive trigger to the AFCI. Try without lights, using only outlet power. Try only one CFL lamp. Try different CFL lamps. Try LED lamps.
  • the breaker sockets in the panel have a means to detect the AFCI, and won't work with an ordinary breaker.
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If your combination arc-fault circuit interrupter (AFCI) breaker is tripping with no load, it means you have an arcing fault in the wiring, you've installed the breaker incorrectly, or the breaker is faulty.

See this answer for more details on what causes a breaker to trip.

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The AFCI is designed to detect two types of fault. Series fault and Parallel fault. Series fault can be caused by a loose screw or back stab on a device or a bad wire nut. These are bad but they are mostly contained in j-boxes. a parallel fault is caused by directly shorting the hot and neutral (or ground) from pulling wires against staples, boxes, pounding nails in wrong places, etc.. these are worse because they are not usually found in the confines of a j-box.

An AFCI is not supposed to trip with the absence of a load.

Possibility: If the (properly functioning) AFCI is tripping with no load, you have a parallel fault. the electrical potential skips across the fault to complete the circuit. if it is a high resistance fault and you give it a light load, the load may have a lower resistance than the fault so the circuit works properly until there is a fluctuation in the voltage- then the power flows across the fault again.

Remedy: Check each box for missing tape or wire nuts. examine the boxes for electrical arcing if they are metal boxes. Tighten the side screws on each device and wrap the device with two layers of electrical tape. This can stop arcing between the hot of one outlet and the neutral of another in quad outlets, and the hot to the box in metal boxes. Also, check the insulation for nicks and missing sections. If you find any, wrap in at least two layers of electrical tape or replace wit pigtail or cut short if the wire is long enough. If possible inspect the run in an attic or basement/crawl space.

Also check again to make sure that there is truly no load on the line. there may be an outlet that you forgot that something is plugged in , or door bell transformer or humidifier, etc.. Disconnect from panel completely and ohms it at the source.

When you tried the standard breaker, did you remember to put the neutral back in the bar? This could account for the circuit not working at all...

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Nice explanation. Another possibility is that there is a neutral->ground fault. AFCI breakers will often detect these (and helped me find two places in my house where a screw was driven through the NM-B and shorted ground->neutral). It would be good to know if the tripping happens when some more "normal"/resistive load is used. –  Pigrew Sep 23 '13 at 3:10

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