AFCI nuissance tripping

[paulgarett]

Installed new AFCI; it trips. Traced the circuit. Disconnected a power out (hot and neutral) at a switch box, which caused the AFCI to stay on.
This power out supplies power to the living room outlets, no lights. Nothing was plugged in. I checked the resistance between the hot and neutral at the switch box and got about 175 ohms. Did not have time to fix problem. Reconnected wires, put a standard breaker in, and it holds fine. What would cause this resistance reading? There are no lamps on this circuit and everything was unplugged. I assume this resistance reading has something to do with the AFCI tripping.

 

[GoldDigger]

Installed new AFCI; it trips. Traced the circuit. Disconnected a power out (hot and neutral) at a switch box, which caused the AFCI to stay on.
This power out supplies power to the living room outlets, no lights. Nothing was plugged in. I checked the resistance between the hot and neutral at the switch box and got about 175 ohms. Did not have time to fix problem. Reconnected wires, put a standard breaker in, and it holds fine. What would cause this resistance reading? There are no lamps on this circuit and everything was unplugged. I assume this resistance reading has something to do with the AFCI tripping.

A resistance of 175 ohms at 120 volts is about 82 watts. For a true no-load situation, that is unacceptable!
It looks like either the circuit goes somewhere else that you have not traced or there is a damaged conductor somewhere that the AFCI is trying to warn you about. It needs to be understood and if necessary fixed! It could easily be the ground fault detector in the AFCI that is tripping, not the arc fault detector.

(There may be some additional load like a doorbell transformer or a timer motor that could explain the reading and draw far less current/power from 60Hz. AC.)

 

[paulgarett]

Thanks for the response. A dangerous situation is not good. Just to confirm, when their is no power applied, the resistance is about 175 ohms between the two outgoing circuit conductors at a junction box. Do you have any recommendations on tools that may be useful to troubleshoot this. Or is plain good ol' troubleshooting techniques the best method?

 

[GoldDigger]

A wire tracer that lets you attach a signal generator to the disconnected wire(s) at the panel and locates the wires with a detector will let you figure out all of the places the wire goes.
The simplest troubleshooting method from there (or instead) is to break the circuit at different junction boxes it goes through to see which side of the break the problem is one.
If it looks like the problem is inside a run of NM, you may have to open the wall.
I would also first check to see whether the resistance is between hot and circuit neutral only or also between hot and ground. A crossed neutral can trip a ground fault detector even in an otherwise intact circuit.
It all comes down to plain old trouble shooting.

Sent from my XT1080 using Tapatalk

 

[kwired]

As golddigger mentioned you seem to have an 82 watt load connected somewhere, and that load itself may not be a problem. What you didn't mention is whether or not you checked continuity/resistance from hot to ground or neutral to ground. Any continuity - even at low megohm ranges from either of those measurements would be more suspicion of a problem that should trip such a breaker than what you have reported measuring.

 

[James L]

Installed new AFCI; it trips. Traced the circuit. Disconnected a power out (hot and neutral) at a switch box, which caused the AFCI to stay on.
This power out supplies power to the living room outlets, no lights. Nothing was plugged in. I checked the resistance between the hot and neutral at the switch box and got about 175 ohms. Did not have time to fix problem. Reconnected wires, put a standard breaker in, and it holds fine. What would cause this resistance reading? There are no lamps on this circuit and everything was unplugged. I assume this resistance reading has something to do with the AFCI tripping.

I'm a little curious. When you say "installed new AFCI" - do you mean you took out an old AFCI and installed a new one, or did you install and AFCI on an existing circuit which used to have a standard breaker? Or is it a new circuit and breaker altogether? It may or may not matter for your situation, but it made me curious.

As for the circuit - did you open each receptacle to verify that this feed does not go any further than this living room?

You just might find an extra feed going out to an outside plug or something

I've seen AFCI breakers trip from a light bulb that has a loose base, from a light switch that was going bad, from a bedroom night light that was flickering because it wasn't quite dark/light enough to make it stay on or off (like in a shadow)

I tripped one by plugging in a night light, because my hand was making a shadow over it.
If you turn a light switch on too slow, it can trip the breaker

In my experience, the dumber a scenario sounds, the more likely it is to be able to trip an AFCI

 

[augie47]

I'm on board with Post #4. Break it down into sections.

 

[ELA]

I would not rely on "theoretical load calcs" based on a high impedance meters resistance measurement. Induced currents could lead to measurement error.
While it may be accurate it could also be in error.

I suggest using a current meter to measure currents to confirm.

 

[kwired]

I would not rely on "theoretical load calcs" based on a high impedance meters resistance measurement. Induced currents could lead to measurement error.
While it may be accurate it could also be in error.

I suggest using a current meter to measure currents to confirm.

True, but higher resistance continuity between the hot and neutral is not much reason for any concern, for no more than what we do know at this point. There has still been no indication of what continuity checks from hot to ground or neutral to ground are like. I would like to know those before proceeding with anything based on hot to neutral readings.

 

[ELA]

The point is that the resistance reading may be nothing more than a distraction.
When dealing with possible problem causing/leakage currents, where ever they may be flowing - Measure currents!

 

[kwired]

The point is that the resistance reading may be nothing more than a distraction.
When dealing with possible problem causing/leakage currents, where ever they may be flowing - Measure currents!

My point though is that current between "hot" and "neutral" is supposed to be seen as normal by the protecting device. Now with the AFCI it is also (allegedly) looking for arcing conditions. A simple resistance test will not tell you if it is/has been arcing, but will indicate there likely is some load whether intentional or not between hot and neutral.

 

[jxofaltrds]

Installed new AFCI; it trips. Traced the circuit. Disconnected a power out (hot and neutral) at a switch box, which caused the AFCI to stay on.
This power out supplies power to the living room outlets, no lights. Nothing was plugged in. I checked the resistance between the hot and neutral at the switch box and got about 175 ohms. Did not have time to fix problem. Reconnected wires, put a standard breaker in, and it holds fine. What would cause this resistance reading? There are no lamps on this circuit and everything was unplugged. I assume this resistance reading has something to do with the AFCI tripping.

My guess is a staple too tight on a NM cable. Good luck finding it.

In one of Mike Holts videos a panel member discusses how he backed his garden tractor over some old dog bedding. Well under that was an extension cord.

I do not recall how long it took but the pressure from the tire cause the wire to heat up and caused a fire.

Would you remove a tripping GFCI and install a standard breaker or receptacle?