Curious problem that started with AFCI

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  #1  
Old 02-04-15, 12:15 PM
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Curious problem that started with AFCI

One for the electricians or electrical engineers out there...I'm a mechanical engineer (my way of apologizing in advance for stupid questions).

Tenants were complaining that a breaker was tripping constantly. They said it's been happening for a month but just got around to telling me because now it trips with any load, even a digital clock radio.

Turns out it's bedroom circuits on an arc fault breaker. The house was built in 2009 so required the arc fault by code for bedrooms. One breaker services all the outlets in 3 bedrooms, 10 outlets as far as I can tell.

I figured faulty breaker, but while I had the panel open I did a quick check for neutral shorts (ohmmeter neutral to ground once it was d/c from breaker) and shows no resistance i.e. short. Now I'm not so convinced it's a breaker issue so I didn't put a new one in yet.

I'm trying to find out if I have a shorted neutral so I plan to connect a standard (non arc fault) breaker to a GFCI and connect the load side to the circuit and the supply side to the breaker. It should sense dissimilar current between hot an neutral, right? If that's the case could the arc fault be tripping due to apparent inductance (my term, not sure what else to call it) of current through the various grounds???

Thanks for any suggestions!
 
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Old 02-04-15, 01:05 PM
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Ground to neutral should show continuity. Hot to ground may show near continuity because of loads connected across hot/neutral.

If you have a second AFCI of the same size swap the leads between the two. If the problem circuit no longer trips it was probably a bad AFCI.
 
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Old 02-04-15, 01:18 PM
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Hey, thanks for the feedback. I thought with the neutral disconnected from the AFCI there would be no continuity to ground. The neutral would go to the receptacles but how would it find ground (unless someone crossed neutrals with another circuit in one of the outlet boxes). With the arc fault circuit the neutral returns to the bus via the AFCI.

I don't have another AFCI to test the cct. All the bedrooms are on one AFCI protected cct. At almost $100 each it's an expensive test but I may not have a choice...
 
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Old 02-04-15, 01:18 PM
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My first diagnostic when working with tripping AFCI breakers, especially early generation ones, is to swap with a new or known good breaker. In my experience the breakers go bad more frequently than they identify real arc faults.
 
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Old 02-04-15, 01:59 PM
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Agreed, nice spare parts business...

I want to be sure I don't have an existing problem with the circuit that may have contributed to the early demise of the AFCI. I'm still a bit concerned about the apparent neutral to ground short with the neutral disconnected from the AFCI.

I should mention I tested the AFCI with most of the circuits disconnected and it would take load. I understand they can be sensitive to wire length so that test was not necessarily conclusive.

Thanks!
 
  #6  
Old 02-04-15, 06:17 PM
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I'm still a bit concerned about the apparent neutral to ground short with the neutral disconnected from the AFCI.
An AFCI breaker senses arcing and then trips. I don't think a neutral to ground contact will trip an AFCI breaker because generally a neutral to ground contact within the branch circuit doesn't create an arc. Knowing that the CEC in many respects shadows the NEC, were combination type AFCI breakers required in 2009 when your house was built as was required by the NEC? If so, the combination type protects against both parallel and series arcing. Parallel arcing could be hot wire to neutral or hot wire to ground. A series arc generally would be when there is a break in either a hot conductor or neutral conductor. The series breaks causing series arcs could be found within something as simple as a loose wirenut.

And remember, an AFCI breaker also trips on overloads and direct shorts.

The house was built in 2009 so required the arc fault by code for bedrooms. One breaker services all the outlets in 3 bedrooms, 10 outlets as far as I can tell.
One breaker? Aren't there any hardwired and interconnected smoke detectors required up there in bedrooms, they are also outlets and have to be AFCI protected by the NEC, but the CEC may be different.
 
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Old 02-04-15, 06:55 PM
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Yeah, not sure about the smoke detectors, I have to check. I'll assume the AFCI is shot and replace it, I had just hoped for an explanation of the apparent short between neutral and ground in the branch circuit outside the panel. With the neutral not connected to the bus bar in the panel I don't understand why it shows zero resistance to ground.

Update...smoke detectors seem to be on the same circuit.

$90 later and a new breaker made zero difference. Circuit still trips with any small amount of load. Any electrical types out there with suggestions???
 

Last edited by Big Yak Attack; 02-04-15 at 09:08 PM.
  #8  
Old 02-05-15, 05:36 AM
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I had just hoped for an explanation of the apparent short between neutral and ground in the branch circuit outside the panel.
Unless there is an arc, a neutral in contact with ground shouldn't trip an AFCI breaker. A neutral can easily come into contact with the EGC at any receptacle.

$90 later and a new breaker made zero difference. Circuit still trips with any small amount of load.
How long does it take the AFCI breaker to trip? One second, three seconds, five seconds? How much load? I haven't had a great deal of direct experience with AFCI breakers, but I did learn at the Eaton Experience Center that an arcing condition takes several seconds to trip an AFCI breaker. What have you done so far in searching for the arcing problem?
 
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Old 02-05-15, 05:55 AM
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Just curious ,what brand of AFCI are we dealing with?
Geo
 
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Old 02-05-15, 06:08 AM
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It's a Federal Pioneer panel, Stab Lok breakers.

The trip is instant, as soon as I power up anything on the circuit. I've opened all the receptacle boxes and they all look fine. The only device boxes I haven't looked in are the hard-wired smoke detectors. I guess that's next...
 
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Old 02-05-15, 07:47 AM
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Can you determine roughly how the circuit may be run,you might want to try and split the circuit up to help isolate the problem, an instant trip almost seems like a short.does a regular breaker trip?
The strange thing is those breakers are the same thing as our Federal Pacific and were junk here ,they never tripped when they should.
Geo
 
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Old 02-05-15, 06:21 PM
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The trip is instant, as soon as I power up anything on the circuit.
What exactly do you mean by that? Does the breaker never reset and trip immediately as you try to reset it? An immediate trip is not from an arcing condition. What do you mean by.......

as soon as I power up anything on the circuit
 
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Old 02-05-15, 09:07 PM
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I meant that when I unplug or turn off everything I can reset the breaker and all's good. If I plug in any device and turn it on, even a clock radio, the breaker trips again. So far I've only found 10 receptacles on the circuit, no other loads. Possibly smoke detectors, but I really hope not. Seems like a bad idea.

Next step is to test with a standard breaker to verify it's tripping from a short and not an arc fault. Then start pulling receptacles and try to isolate where the issue is...
 
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Old 02-06-15, 04:36 AM
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If you can reset with everything unplugged but with the smoke detectors still on,that would seem to prove that the detectors are not the problem,the detectors do go off with that breaker turned off correct?
Geo
 
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Old 02-06-15, 07:57 AM
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Unless there is an arc, a neutral in contact with ground shouldn't trip an AFCI breaker. A neutral can easily come into contact with the EGC at any receptacle.
I made this statement earlier in this thread and think I should back off on it. I seem to remember that an AFCI breaker also provides some GFCI protection, but not at the 5 mA level required for personnel protection as the new dual function combination AFCI/GFCI breakers provide (I think only Square D and Cutler-Hammer make these so far). I seem to remember that the AFCI breaker's GFCI protection level is somewhere around 30mA. That would mean that a neutral to ground contact somewhere within the circuit or connected equipment might immediately trip the combination type AFCI breaker.

Just a thought, hope it helps.



I just found info to back up this post.

How do I determine if I have a grounded or shared neutral?

One of the most common problems that cause the AFCI to trip is grounded and shared
neutrals. The Eaton Arc Fault Circuit Interrupter has 30ma of ground fault protection built
directly into the breaker itself. If there is a bare ground wire making contact with the
neutral conductor, the breaker will trip instantly as soon as a load exceeding 40 watts is
applied to the circuit.
The best way to test for a grounded neutral is to use an ohm/continuity tester by turning
the breaker to the off position and remove the load neutral from the breaker. Next, take
one lead of your tester to the load neutral and the other lead to the neutral/ground bar in
the panel. You should read no continuity. If you are getting continuity, go through entire
circuit looking for the location where the bare ground is making contact to the neutral
conductor. If you are using shared neutral homeruns, you must use a two pole arc fault
breaker. You can not use single pole arc faults breakers with shared neutrals.
http://www.eaton.com/ecm/groups/publ.../ct_206788.pdf

I hope this link helps you to find your problem.

You could have a neutral/ground contact somewhere within your circuit, like at a receptacle, that would immediately trip a 5 mA rated GFCI breaker, but with the AFCI breaker, it won't trip the breaker immediately till you have a 40 watt load applied to the circuit. The smoke detectors evidently are not 40 watts of load, but the smoke detectors along with the clock radio load may equal 40 or more watts and the breaker trips. Just another thought, hope it helps.
 

Last edited by CasualJoe; 02-06-15 at 08:11 AM. Reason: Found New Info I Was Looking For
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Old 02-06-15, 08:59 AM
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That is very good information, thanks! It's consistent with something I pointed out earlier, an apparent neutral to ground short. When I disconnect the neutral at the AFCI and check to ground I show zero resistance, which in my mind is not right. The only connection from neutral to ground should be in the panel. I had planned to try a GFCI to see if that was indeed the case. The lower threshold of a GFCI should trip.
 
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Old 02-06-15, 11:54 AM
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the breaker will trip instantly as soon as a load exceeding 40 watts is
applied to the circuit.


This is also consistent with what you had said......

The trip is instant, as soon as I power up anything on the circuit.
 
  #18  
Old 02-06-15, 08:58 PM
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Problem solved. One of the screws in a receptacle was contacting the box. Took em all apart and turned all the screws in just so it doesn't happen again. The electrician used the push-ins and not the screws. Kinda wish he had taken a bit more time and turned all the screws in, but I can understand not wanting to spend the time.

Thanks for the help!
 
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Old 02-07-15, 04:46 AM
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Gooid job!! I am glad you found and fixed that problem!

I can't speak for others, but I also found this thread educational.

The electrician used the push-ins and not the screws.
What he did was compliant with Canadian code as far as I know, but just not a good practice.
 
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Old 02-07-15, 07:15 AM
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Yes, good job. I hope you moved the wires to the screws. If not you may have problems later because the back stabs are less reliable.
 
  #21  
Old 02-07-15, 04:23 PM
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Thanks for that info,I also seem to learn from this forum.
Geo
 
  #22  
Old 02-07-15, 04:26 PM
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but I can understand not wanting to spend the time.
You're being too polite and Canadian there, it would have taken him seconds to wrap the wires around the screws. Poor workmanship.
Also, are your smokes on the receptacle circuit? They are required to be on a lighting circuit.
 
  #23  
Old 02-07-15, 06:09 PM
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Also, are your smokes on the receptacle circuit? They are required to be on a lighting circuit.
I haven't seen you in a while Mr.Awesome, welcome back. Question, are the smokes required to be on an AFCI circuit in Canada? Here the best practice is to install a dedicated AFCI circuit for all the interconnected smokes. Of course, the AFCI has been required for several years because the smokes are required in bedrooms here and considered outlets.
 
  #24  
Old 02-07-15, 06:44 PM
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Thanks Joe, haven't had time in the past couple months to sit in front of the computer for awhile.
I just got my new 2015 CEC book in a couple of days ago. I have to flip through it as I've heard AFCIs make a major appearance in this version. We just wrote in that AFCIs are required on all receptacle circuits and not just bedrooms.
Previously though, smokes just had to be interconnected and on a circuit with commonly used lights. No requirement for AFCIs unless bedroom receptacles were on that circuit.
 
  #25  
Old 02-08-15, 04:52 AM
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Hi Joe,I can't find that requirement in the NEC,it maybe in the Life Saftey 101, although it maybe a requirement from the local AHJ.
Geo
 
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Old 02-08-15, 05:11 AM
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Hi Joe,I can't find that requirement in the NEC,it maybe in the Life Saftey 101, although it maybe a requirement from the local AHJ.
Placement of the interconnected smoke detectors is from building codes and fire codes and in this area includes inside each bedroom. I think that's pretty common everywhere now. The smoke detectors being on an AFCI circuit is from the NEC because they are considered an outlet and they are in the bedrooms.
 
  #27  
Old 02-11-15, 10:06 AM
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The smokes were on a different circuit but the CO detector may be on the same circuit, I'll have to trace it next time I'm there.

My old (2002) simplified code book for residential wiring says the smokes can be on any general lighting or plug outlet circuit except ones protected by GFCI/kitchen/bath/exterior. I suspect that's changed in later editions.
 
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Old 02-11-15, 11:23 AM
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For '02 that would be correct. Starting in '05 they were mandated to be on AFCI breakers, which usually meant tying them in with a bedroom to save $40 on a breaker. Some jurisdictions have since backed off that requirement in favor of various other mandates. There is not a lot of consistency in this area.
 
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