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Old 02-15-2011, 01:57 PM   #1
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AFCI problem has me stumped


Ok, while I am no professional electrician... I am pretty comfortable with how home wiring works being an Electrical Engineer.

I just moved into a new house and apparently the current code is to have bedrooms on AFCI breakers, they fault when an arc is detected (which I assume means huge current spike) and trip to prevent fires.

The AFCI in my master bedroom keeps tripping and through a process of elimination I've narrowed it down to the lights in the hallway. Everytime the lights are on in the hallway the AFCI in my master bedroom and only my master bedroom trips.

They are definitely on different circuits... I can turn my master bedroom on/off and my hallway lights on/off independently of each-other at the breakout box and the expected results happen (one is on and the other is off).

I've tried replacing the AFCI breaker for the bedroom, that didn't work. I've gotten new switches thinking there was some arcing going on there, that didn't work. I've pulled the lights out and re-wired them, that didn't work.

At this point I am completely stumped, these aren't a huge current draw or anything.

Any suggestions?

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Old 02-15-2011, 02:06 PM   #2
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AFCI problem has me stumped


I'm no electrician either, but here's a suggestion...when the receptacles were installed did you "back-stab" the connections? Notorious for loose connections.

Also, have you calculated the total amperage of all loads on the circuit to make sure it doesn't exceed the amp rating of the AFCI?

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Old 02-15-2011, 02:13 PM   #3
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AFCI problem has me stumped


Quote:
they fault when an arc is detected (which I assume means huge current spike)
that in itself is not true. Since there are many arcs that are acceptable such as when a switch is flipped, certain motors run, or even when a plug is plugged in or removed, it requires much more than the simple detection of an arc. This is from wikipedia:

Quote:
AFCIs use unique current sensing circuitry to discriminate between normal and unwanted arcing conditions.
and the "current code" varies from locality to locality. In many (most actually) the 2008 code is in force. That requires afci on almost all circuits in a house.

so, do the hall lights and the bedroom circuit in question share a neutral (multiwire branch circuit)?

are the breakers for the two circuits next to each other in the panel?

If the answers are no and yes, try relocating the breakers so they are not next to each other.

Since you have found the association of the hall lights being on to the bedroom breaker tripping, is there something in the bedroom being switched at that moment the breaker trips or is it random?
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Old 02-15-2011, 03:27 PM   #4
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AFCI problem has me stumped


Hi,

If you have an arcing circuit on the same phase as the afci breaker it may trip. This happened to me and so I can attest to the high sensitivity of these devices. You could swap the AFCI circuit breaker to the other phase in your panel that might solve it. I better solution though would be to check for problems in the 'hall light' circuit that is causing your problem.
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Old 02-15-2011, 03:30 PM   #5
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AFCI problem has me stumped


When you say you "pulled the lights and rewired" were you talkign about the hall lights or the bedroom lights?
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Old 02-15-2011, 03:32 PM   #6
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AFCI problem has me stumped


If the breakers were next to each other in the panel they would be on opposite phases and he would not have the AFCI tripping because of the arc in the hall circuit. I think he wants the breakers to be beside each other or at least on opposite phases.
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Old 02-15-2011, 04:00 PM   #7
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AFCI problem has me stumped


Quote:
Originally Posted by fabrk8r View Post
Also, have you calculated the total amperage of all loads on the circuit to make sure it doesn't exceed the amp rating of the AFCI?
Its not even close... two 15A circuit breakers handling 2 lights and 1 TV (at most, this has happened when nothing was plugged in the m. bedroom) respectively.

I don't know what you mean by "back-stab," I've tested the rec's with a little tester and the tester says they are good.

Last edited by WR_ECE; 02-15-2011 at 04:05 PM.
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Old 02-15-2011, 04:02 PM   #8
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AFCI problem has me stumped


Quote:
Originally Posted by nap View Post
so, do the hall lights and the bedroom circuit in question share a neutral (multiwire branch circuit)?

are the breakers for the two circuits next to each other in the panel?

If the answers are no and yes, try relocating the breakers so they are not next to each other.

Since you have found the association of the hall lights being on to the bedroom breaker tripping, is there something in the bedroom being switched at that moment the breaker trips or is it random?
I believe they share a neutral and a phase actually, and yes they are next to each-other (one above the other to be specific).

There is no dependence on something being on in the bedroom, this happened when there wasn't even anything in the bedroom electrically.

Quote:
Originally Posted by trosenda View Post
When you say you "pulled the lights and rewired" were you talkign about the hall lights or the bedroom lights?
hallway lights, the ceiling lights in the bedroom is on its own circuit and that circuit is not tripping. Hallway lights cause the master bedroom receptacles to trip.

Last edited by WR_ECE; 02-15-2011 at 04:05 PM.
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Old 02-15-2011, 04:05 PM   #9
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AFCI problem has me stumped


If they share a neutral they're not on the same phase. If the two circuits share a neutral they have to be on different phases otherwise you can end up with 15 x 2 amps on the neutral if both circuits are at full capacity and the 14 gauge wire can't handle that. You need to a) find your arc in the hall light circuit OR b) run a dedicated neutral to one of the circuits OR C) remove the AFCI.

Also, if the breakers are next to each other in the panel they are on opposite phases. If, as you say, the two circuits have a common neutral then they must stay on opposite phases (best achieved by having them side by side in the panel). If you mess with that you're creating a fire hazard.

Last edited by trosenda; 02-15-2011 at 04:16 PM.
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Old 02-15-2011, 04:27 PM   #10
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AFCI problem has me stumped


also make sure a ground and neutral are not touching each other.may not be touching now but a little vibration can cause them to touch.
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Old 02-15-2011, 04:35 PM   #11
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AFCI problem has me stumped


You can NOT "share" a neutral on a MWBC with an arc-fault breaker. I doubt this is the problem here.

We had a similar problem where the lady would run the vacuum in the master bedroom, and it would trip out the AFCI breaker in the room across the hall!!

The vacuum would continue to operate, oblivious to what happened on the other circuit.

And, no, there were no interconnection or cross-circuits of any neutral wires on either of those circuits.

We replaced all the AFCI breakers in the panel, and the problem went away.

If that doesn't work, then I would ask the OP if there are any multi-gang boxes that share both circuits? Such as a 2-gang switch box that has both the hallway switch and one for the bedroom? There may be an interconnection in there ... somewhere ...
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Old 02-15-2011, 05:05 PM   #12
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AFCI problem has me stumped


Quote:
kbsparky;591703]You can NOT "share" a neutral on a MWBC with an arc-fault breaker. I doubt this is the problem here.
Siemans gives directions for using acfi's on a MWBC and way back in 2002, Square D said the technology was available but had not been introduced simply due to lack of demand.

https://www.sea.siemens.com/us/inter...ting-Guide.pdf
Quote:
If the AFCI is a single pole device determine whether 
the AFCI has been wired to a multi-wire branch circuit
(shared neutral). Single-pole AFCIs cannot be wired
this way. It will not perform properly when wired to
a multi-wire branch circuit and will trip persistently
(although this may not become apparent until a load
is applied to at least one of the circuits). Each single-
pole AFCI must have a neutral wire unique to that
branch circuit. For multi-wire branch circuits, a two-
pole AFCI must be used. Siemens two-pole AFCIs
offer a common trip between the two poles, reducing
the chance for a shock hazard when one circuit on
a multi-wire branch circuit is energized and the other
Multi-wire branch circuit one is de-energized.
inspections and repairs should be performed only by
ed electricians
http://ecatalog.squared.com/pubs/Cir...B0201R1102.pdf


Quote:
Can AFCIs be used in multi-wire circuits with a
shared neutral?
Single-pole AFCIs cannot protect circuits in which the neutral (grounded
circuit) conductor is shared or mixed. The reason for this is that current
flowing out and returning is monitored for the presence of arcing faults.
When one-pole AFCIs are applied, the circuit must have a distinct hot and a
distinct neutral conductor. Otherwise, the AFCI cannot distinguish arcing
ground-fault occurrences.
We can expect general availability of two-pole AFCIs for this application at
some point in the future, since present technology is readily capable. The
two-pole AFCI has not been generally introduced because of limited demand
at present
and a Seimans breaker that is designed for the purpose:

http://www.sea.siemens.com/us/Produc...Type_AFCI.aspx



Quote:
If that doesn't work, then I would ask the OP if there are any multi-gang boxes that share both circuits? Such as a 2-gang switch box that has both the hallway switch and one for the bedroom? There may be an interconnection in there ... somewhere ...
I would suspect, if this really isn't a MWBC that the neutrals might have been crossed somewhere.
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Old 02-15-2011, 05:50 PM   #13
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AFCI problem has me stumped


I am wondering if this AFCI breaker was added later and is on a MWBC. If this is the case I have seen tricks work sometimes, like taking the AFCI breaker out and putting a AFCI recepticle in at the first opening in the bedroom, and add a longer than normal pigtail wire on the neutral conductor. If this doesn't work I can only say that you would need to run a new homerun with a dedicated neutral to the bedroom to stop the tripping.
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Old 02-15-2011, 05:58 PM   #14
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AFCI problem has me stumped


I agree with spark and arc; with respect to the AFCI being added after the circuits were designed. I think the only solution is rewiring to eliminate the shared neutral.

Last edited by trosenda; 02-15-2011 at 06:15 PM.
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Old 02-15-2011, 06:06 PM   #15
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AFCI problem has me stumped


Quote:
If this is the case I have seen tricks work sometimes, like taking the AFCI breaker out and putting a AFCI recepticle in at the first opening in the bedroom, and add a longer than normal pigtail wire on the neutral conductor.

well, from what I understand, it wouldn't meet code

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