AFCI Troubleshooting

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mkgrady

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Massachusetts
I am having a problem with a tripping AFCI on a newly wired home (by me). We are just starting to turn on circuits and one of them will not hold if there is ANY load on it. Without a load it does not trip. I ran out of time on it today but hope to go back with some ideas to make the fix easier. I'm going back tomorrow to continue troubleshooting. I am really confused by the circuit holding with no load but tripping with a load. Here is what I have so far:

It is a 15 amp general purpose circuit in a master bedroom and bathroom all run in romex
The circuit holds if connected to a regular 15 amp CB (not a surprise)
Three different AFCI breakers have been tried.
I assume the neutral and ground are not touching downstream of the breaker because the breaker holds with no load.
The circuit trips with a 60 watt bulb connected. I tried different bulbs and sockets.

The only thing I can think of is the hot or neutral have such a poor connection somewhere that it is arcing once a load is applied. That really seems unlikely given that everything is new. I think I make pretty good connections with my wire nuts and all receptacles are pigtailed.

Any ideas would be appreciated?
 
mkgrady said:
I am having a problem with a tripping AFCI on a newly wired home (by me). We are just starting to turn on circuits and one of them will not hold if there is ANY load on it. Without a load it does not trip. I ran out of time on it today but hope to go back with some ideas to make the fix easier. I'm going back tomorrow to continue troubleshooting. I am really conf asused by the circuit holding with no load but tripping with a load. Here is what I have so far:

It is a 15 amp general purpose circuit in a master bedroom and bathroom all run in romex
The circuit holds if connected to a regular 15 amp CB (not a surprise)
Three different AFCI breakers have been tried.
I assume the neutral and ground are not touching downstream of the breaker because the breaker holds with no load.
The circuit trips with a 60 watt bulb connected. I tried different bulbs and sockets.

The only thing I can think of is the hot or neutral have such a poor connection somewhere that it is arcing once a load is applied. That really seems unlikely given that everything is new. I think I make pretty good connections with my wire nuts and all receptacles are pigtailed.

Any ideas would be appreciated?
Click to expand...
This sounds like a neutral to ground fault. What brand breaker?
 
This sounds like a neutral to ground fault.
Click to expand...

Disconnect all wires at the breaker, nothing connected to the receptacles and no switches on. Take your ohmmeter and check for continuity between all three conductors, in particular the ground and white. Should read infinity all around- in other words the same as if the test leads were connected to nothing.

-Hal
 
hbiss said:
Disconnect all wires at the breaker, nothing connected to the receptacles and no switches on. Take your ohmmeter and check for continuity between all three conductors, in particular the ground and white. Should read infinity all around- in other words the same as if the test leads were connected to nothing.

-Hal
Click to expand...

I will try that. But still if there were continuity where I shouldn't wouldn't the circuit trip as soon as the breaker is turned on? That is my understanding. Maybe I have that wrong.
 
ActionDave said:
No. AFCIs have a high enough threshold, 30 milliamp, that they won't trip on a neutral to ground fault unless there is a load.
Click to expand...

That is good to know. Thanks. It will change my approach to troubleshooting this tomorrow. Sounds like I have a N to G fault which should not be difficult to find.
 
mkgrady said:
I am having a problem with a tripping AFCI on a newly wired home (by me). We are just starting to turn on circuits and one of them will not hold if there is ANY load on it. Without a load it does not trip. I ran out of time on it today but hope to go back with some ideas to make the fix easier. I'm going back tomorrow to continue troubleshooting. I am really confused by the circuit holding with no load but tripping with a load. Here is what I have so far:

It is a 15 amp general purpose circuit in a master bedroom and bathroom all run in romex
The circuit holds if connected to a regular 15 amp CB (not a surprise)
Three different AFCI breakers have been tried.
I assume the neutral and ground are not touching downstream of the breaker because the breaker holds with no load.
The circuit trips with a 60 watt bulb connected. I tried different bulbs and sockets.

The only thing I can think of is the hot or neutral have such a poor connection somewhere that it is arcing once a load is applied. That really seems unlikely given that everything is new. I think I make pretty good connections with my wire nuts and all receptacles are pigtailed.

Any ideas would be appreciated?
Click to expand...

Does it trip instantly after you add a load to the circuit? If not, I believe it could be a ground fault between the neutral and the EGC. Replace the AFCI cb with a GFCI cb. (you could use a meter but this method works well when I am alone on the job) If it trips instantly after you do that then open the circuit at the first box in the run and start the process of elimination
 
I installed a Siemens dual function breaker recently ...... It had an indicator light that would tell you the type of fault. Maybe if you have one of those laying around you can install and see what indication it gives.


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Another possibility,

Normally with the Siemens afci if the neutral and ground are solidly touching it will trip right away but if a neutral and ground are ever-so-close but not to register on a ohm meter as a short it can cause a trip once the circuit is loaded.

For example, one time I had this same problem and found that one of the 8-32 screws that mount a closet fixture had worn into the neutral wire of the fixture as it was driven in. In doing so it made a pinhole breach of the conductor...almost shorting to the grounded mounting screw.

Sometime I'll have to find a picture of it to show. Had to magnify in order to see the pin hole.
 
Knuckle Dragger said:
Does it trip instantly after you add a load to the circuit? If not, I believe it could be a ground fault between the neutral and the EGC. Replace the AFCI cb with a GFCI cb. (you could use a meter but this method works well when I am alone on the job) If it trips instantly after you do that then open the circuit at the first box in the run and start the process of elimination
Click to expand...

Yes it trips instantly when a load is turned on. Not sure what that tells me.
 
brantmacga said:
I installed a Siemens dual function breaker recently ...... It had an indicator light that would tell you the type of fault. Maybe if you have one of those laying around you can install and see what indication it gives.


Sent from my iPhone using Tapatalk
Click to expand...

I don't have that feature on that breaker. I can get one tomorrow and try that. So far the most likely suspect seems to be G to N fault. I would not expect the indicator to show arc fault in that case. Would it shown ground fault? I think of a ground fault as hot to ground not neutral to ground
 
mkgrady said:
...
I assume the neutral and ground are not touching downstream of the breaker because the breaker holds with no load.
...
Click to expand...
AFCIs do not work that way. The AFCIs that still have ground fault protection, only trip for a grounding to neutral connection when there is load
 
mkgrady said:
I am having a problem with a tripping AFCI on a newly wired home (by me). We are just starting to turn on circuits and one of them will not hold if there is ANY load on it. Without a load it does not trip. I ran out of time on it today but hope to go back with some ideas to make the fix easier. I'm going back tomorrow to continue troubleshooting. I am really confused by the circuit holding with no load but tripping with a load. Here is what I have so far:

It is a 15 amp general purpose circuit in a master bedroom and bathroom all run in romex
The circuit holds if connected to a regular 15 amp CB (not a surprise)
Three different AFCI breakers have been tried.
I assume the neutral and ground are not touching downstream of the breaker because the breaker holds with no load.
The circuit trips with a 60 watt bulb connected. I tried different bulbs and sockets.

The only thing I can think of is the hot or neutral have such a poor connection somewhere that it is arcing once a load is applied. That really seems unlikely given that everything is new. I think I make pretty good connections with my wire nuts and all receptacles are pigtailed.

Any ideas would be appreciated?
Click to expand...

I test it like I would if I had a GFCI breaker tripping.

Remove the offending circuit's wiring from the breaker (hot and neutral) and ground bar (EGC); make sure all switches are off, all devices unplugged. Check for continuity from ground to neutral on the wires of the tripped circuit; you should have infinity. If you have a reading, check to see if you have a ground touching the neutral screws on a receptacle, or a pinched wire in a luminaire or paddle fan (most common problems Ive found). Then check to see if you have continuity between your neutral wire and the neutral/ground bar in the panel; should have infinity. If you had infinity on the previous test, but now have a reading, you have tied together neutrals of different circuits. If you can remember the first box that homerun hit, open it up. If not, I check multigang switch boxes first.

If there is a drywall screw penetrating the NM bridging the neutral and ground, it will hold under no load but even a GFCI outlet indicator light will trip the AFCI.

You already wrote that you had the circuit's neutral on the breaker, and the neutral pigtail to the neutral bar which is correct. Make sure the neutral on that breaker is the one that should be paired with its hot. I assume since you wired the house you know if there is a MWBC involved.

You could also replace the AFCI with a regular breaker, then check lights for a socket that doesnt work. In cheapie multi-bulb fixtures, like are often installed in bathrooms over vanities, I've found neutrals popped out of the factory connections/wirenuts that are touching the grounded frame of the fixture. Lights also seem to be the main culprit for wires getting pinched between the frame and the drywall, or skinned and shorted when maneuvered thru the tie bar/box mounting plate.

Good luck, please let us know what you find!
 
hbiss said:
Disconnect all wires at the breaker, nothing connected to the receptacles and no switches on. Take your ohmmeter and check for continuity between all three conductors, in particular the ground and white. Should read infinity all around- in other words the same as if the test leads were connected to nothing.

-Hal
Click to expand...
That's the place to start. Look at the receptacles as when using NM cable the bare EGC can fold back as long the side of the neutral side of the receptacle and lean up again the neutral screw terminal when pushing the receptacle back in the box. As such part of the neutral current now is cspable of returning of the EGC and the AFCI will read is as a ground fault. Reading continuity between the white and EGC as previously described should show that.
 
mkgrady said:
I don't have that feature on that breaker. I can get one tomorrow and try that. So far the most likely suspect seems to be G to N fault. I would not expect the indicator to show arc fault in that case. Would it shown ground fault? I think of a ground fault as hot to ground not neutral to ground
Click to expand...

It has indicator lights for both.

Neutral to ground will show up because it would cause an imbalance on the neutral return.


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