Troubleshooting AFCI Ckt

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jmellc

Senior Member
Location
Durham, NC
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Facility Maintenance Tech. Licensed Electrician
We've been troubleshooting an AFCI circuit that is maddening. Apartment job another company roughed in. Breaker holds as long as no load. Any switch we turn on trips it. Tried a standard breaker & it holds OK, no matter the load.

Logic would tell me we have a hot/neutral arc beyond each switch. Probability tells me this is highly unlikely. Ckt feeds a bedroom, bathroom, closet & kitchen lights. Even with sloppy work, what's the chance of overdriven staples in line beyond each switch?

We also tried another AFCI to be sure we didn't have a dud. We are trying to avoid cutting walls and ceilings but we're running out of options.
 
Off the top of my head I would say you have neutral to ground fault, tied neutrals or crossed neutrals. I say this because it holds with no load, but when load is applied it trips- which tells me that the current imbalance created by the wiring error is tripping the 30/50ma GFP inside the AFCI.

Megging the circuit is a good place to start.
 
If any switch you turn on trips the circuit my money is ground and neutral contact in the circuit.

Worst arc fault trouble shoot was when someone nicked the conductors stripping the wire in a light box. It would hold for hours even days depending on use but usually trip when i wasn't there.
 
Little Bill said:
Put in a GFCI breaker in place of the AFCI and see if it trips. If it does, it's a ground-neutral fault.
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Remove all loads, and lift the ground and neutral off the busbars and ohm it out.

Another possibility is someone tied a bunch of different circuit neutrals together in a box.
 
We installed AFCI at a service change on an older home about two weeks ago and One started tripping a week later. Help says the trip code worked great. Self diagnosed as failed internally. Replace breaker. Warranty. :thumbsup:

Use the brands with that capability. It will make your life easier.
 
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Neutral to Ground connection somewhere in the circuit. Open circuit at certain points to diagnose. I traced one to a light fixture. I traced another to a sloppy receptacle install with ground wire touching neutral screws on device.
 
ptonsparky said:
We installed AFCI at a service change on an older home about two weeks ago and One started tripping a week later. Help says the trip code worked great. Self diagnosed as failed internally. Replace breaker. Warranty. :thumbsup:

Use the brands with that capability. It will make your life easier.
Click to expand...

I haven't been living under a rock but I haven't heard of this breaker. We have to use the brand that fits the panel. Homeline panels were installed long before we got the job.

What brand is this trip code breaker? Maybe we could set up a test box of some sort with it.
 
Thanks for the feedback but I can't buy neutral/ground short. If that were the case, the breaker would never hold to begin with. We fixed a few of these in neighboring apartments.

We may go back through all switchboxes but I don't expect to find any crossed neutrals there because I am sure there are no boxes with multiple circuits.

Still open for ideas. I am not on that job much but I told my coworker to also check for any possible double feed to the circuit from other apartments. We found 1 AC circuit crossed from 1 apartment to another. I have occasionally seen double feeds to a circuit from same panel and it could be plausible to be crossed up. The co. that started this is one of the big boys here. I used to work for them and know some of the disasters they have done on similar projects.
 
jmellc said:
Thanks for the feedback but I can't buy neutral/ground short. If that were the case, the breaker would never hold to begin with. We fixed a few of these in neighboring apartments.

We may go back through all switchboxes but I don't expect to find any crossed neutrals there because I am sure there are no boxes with multiple circuits.

Still open for ideas. I am not on that job much but I told my coworker to also check for any possible double feed to the circuit from other apartments. We found 1 AC circuit crossed from 1 apartment to another. I have occasionally seen double feeds to a circuit from same panel and it could be plausible to be crossed up. The co. that started this is one of the big boys here. I used to work for them and know some of the disasters they have done on similar projects.
Click to expand...

Sure it would hold, there is not current. GFP works on the premises of current imbalance, not current no imbalance. As load is applied some goes down the neutral some down the ground- when the level of current imbalance as sensed by the torrid coil exceeds 30 to 50ma, the breaker trips.
 
mbrooke said:
Sure it would hold, there is not current. GFP works on the premises of current imbalance, not current no imbalance. As load is applied some goes down the neutral some down the ground- when the level of current imbalance as sensed by the torrid coil exceeds 30 to 50ma, the breaker trips.
Click to expand...

I have tripped AFCI's a number of times when wiring lights with switch off. No power to light but I would trip breaker if I hit neutral and ground together. I did it by accident a few times and on purpose just to verify. I've done it with Homeline and GE AFCI's.
 
jmellc said:
I have tripped AFCI's a number of times when wiring lights with switch off. No power to light but I would trip breaker if I hit neutral and ground together. I did it by accident a few times and on purpose just to verify. I've done it with Homeline and GE AFCI's.
Click to expand...

Either there was power on that circuit somewhere, or that particular AFCI had neutral to ground logic which basically injects a signal into the neutral that if grounded down it trips the breaker. Someone posted a link not to long ago in another thread.
 
jmellc said:
I have tripped AFCI's a number of times when wiring lights with switch off. No power to light but I would trip breaker if I hit neutral and ground together. I did it by accident a few times and on purpose just to verify. I've done it with Homeline and GE AFCI's.
Click to expand...

If the switch is off, you've only disconnected the ungrounded conductor from the circuit. The neutral and ground are still electrically connected to the AFCI. If there's a load on that circuit, touching the ground and neutral will create a ground fault.
 
jmellc said:
I have tripped AFCI's a number of times when wiring lights with switch off. No power to light but I would trip breaker if I hit neutral and ground together. I did it by accident a few times and on purpose just to verify. I've done it with Homeline and GE AFCI's.
Click to expand...



https://goodsonengineering.com/wp-c...-AFCI-EFFECTS-ON-ARC-MAPPING-A-FIRE-SCENE.pdf


NOT ALL AFCI’S ARE CREATED EQUAL
The reader is cautioned that not every AFCI works the same. Basically, every AFCI is designed to test for the signature of an arcing connection. However, this is where the similarity ends. It is necessary for the investigator to know more about the brand and model of ACFIs in use. Why? Because the manufacturers have added other safety features in the AFCIs, of which, there is no uniformity among manufacturers. More specifically, manufacturers have included the following types of features in their various circuit protection devices

:
Ground Fault Circuit Interrupter (GFCI)
Ground Fault Equipment Protection (GFEP)
Grounded Neutral Sensor (GNS)

Most are familiar with the GFCI circuit protection device, which responds to a current imbalance of 5 mA or more between hot and neutral. The GFEP is similar, but is NOT listed for shock protection

– a typical imbalance or trip value is 30 to 50 mA. The GNS senses a condition whereby the ground and neutral are shorted together downstream; when this happens, the Equipment Grounding Conductor (EGC) is electrically in parallel with the neutral, allowing the EGC to carry current in normal operation – a condition that is absolutely forbidden by the NEC.


Any one of these features (GFCI, GFEP, GNS) may be present in the specific circuit protection device which is associated with the circuits being examined at a scene. The circuit protection device can be tripped in association with any one of these features in reaction to the fire, along with the AFCI circuitry, as we ll as from direct heat impingement on the device.

As an example, a neutral touching a ground conductor (EGC) on an unloaded circuit will cause the AFCI to trip. Without being aware of this phenomenon, the investigator may incorrectly conclude the status of the power to the downstream circuitry prior to the fire.
Click to expand...
 
We finally found a switch leg to a bath fan with an overdriven staple. That took care of it. I was happy to get it working but still wonder how hitting other switches would make a difference. Too many mysteries sometimes.
 
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