tripping afci

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Old 01-25-19, 04:46 PM
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tripping afci

For the last 12 months my 2nd floor lighting + outlet circuit, with a Siemens Combo AFCI breaker, has tripped a few times. At the point of each trip I made a half hearted effort to work out what happened, but I couldn't reproduce it. Today it happened again and I decided to get properly in to it.

After some time unplugging things and checking wiring in receptacles, I came up with nothing. I thought maybe the AFCI breaker was going bad, so I switched it with a dual function GFCI/Combo AFCi Siemens breaker. Much to my surprise with the DF breaker in, and the panel re-energized, the 2nd floor bedroom circuit tripped immediately and would not come on at all. I went through all my outlets and switches again and made sure everything was off and unplugged. Back to the panel, flip the DF breaker, and it comes on and stays on now. I set off plugging things back in and flicking lights back on and eventually I got to the problematic light switch. It was then that it became clear what was going on.

Roughly around a year or so - maybe a little more - in this very same switch box, I had a contractor install a smart light switch which required a neutral pulling from a nearby outlet. What he either did not know, or did not care to mention, was that the outlet he pulled the neutral from was on a different circuit. The outlet he pulled from is dedicated to my washing machine. To be fair, I was not aware that the washing machine had a dedicated circuit. Never noticed it in the panel.

Anyway, I've come up with what I think are few options for solving this, and I think I know what is probably the best one, but I would appreciate any feedback.

For the sake of clarity I'll call the 2nd floor circuit A, and the washing machine circuit B.


a) I could open the switch box on circuit A, cap the circuit A line coming in, and pull circuit B's line in, so the switch and light receives line/neutral both from circuit B. However, the neutral from the light fixture does not come back to the box. So in this configuration - does moving the switch on to the other circuit satisfy the AFCI safety on circuit A, and so could it maintain either a Combo AFCI or DF without further trip issues? And still in this configuration, presumably, circuit B (which presently has neither AFCI/GFCI) would still work, but then couldn't have AFCI because it'd trip in the same way Circuit A has been doing?

b) Back in the panel, where there is a lot of junction wiring already, I could tie circuit A and circuit B together, the line and neutrals both, and then feed them in to a single pole AFCI or DF? The main issue here is one of load - there's not much on circuit A, until summer when we do have a couple of air conditioners on it. So I feel like I should probably keep the washing machine on its own dedicated circuit.

c) Also back in the panel, I could tie the neutrals for A + B, and then feed that and the independent A+B circuits in to a dual pole combo AFCI? This gets me combo AFCI on my 2nd floor circuit, and gets me AFCI on my laundry circuit to. So I should eliminate my tripping, and I gain another circuit with AFCI protection. I think.

Are there other options? I am thinking I should do C.
 
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Old 01-25-19, 05:53 PM
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Welcome to the forums.

I had a contractor install a smart light switch which required a neutral pulling from a nearby outlet.
Hopefully not an electrician as that is 100% wrong.

Before you even consider a "workaround". Both circuits need to use the same size wire. Your washer circuit is more than likely #12. What does the other circuit use ?

Quite obviousness you have a switch loop. That's where just the hot is sent to the switch and it's switched coming back. In order to use a different circuit to feed that light...... you will have to disconnect the light from the current circuit and use the two wires from the switch to supply the light with hot AND neutral.

Circuit A will remain unchanged. Circuit B will now need to be protected too.
 
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Old 01-25-19, 06:15 PM
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Hopefully not an electrician as that is 100% wrong.
Yeah - it was a licensed electrician.

Your washer circuit is more than likely #12. What does the other circuit use ?
It is #14.
 
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Old 01-25-19, 06:33 PM
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A neutral, cannot by code, be shared between two circuits.
With two different wire sizes..... your alternate plans aren't going to work.

Was I correct that you only have a white and black wire coming down from the light ?
 
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Old 01-25-19, 07:44 PM
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The switch box has the "foreign" neutral pulled in, and then just two other wires. One is on the line side of the switch, the other is on the load side.

If the wire gauges were the same, is the (c) workaround sound, electrically at least, if not code wise?

From what I can gather, pig tailing the neutrals for the two circuits in the panel and then using a dual pole AFCI should:

a) ensure both circuits get de-energized at the same time so no surprises can happen if one is off but not the other
b) ensure both circuits are on different phases so that load on the neutral is balanced (?)
c) give both circuits afci protection
 
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Old 01-26-19, 06:26 AM
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quote by pjmax....."A neutral, cannot by code, be shared between two circuits."
This isn't correct. The NEC does allow the sharing of a neutral in a multi branch setup under Article 100. You see this a lot in commercial wiring were multiple branches are ran through conduit with outlets. They share a neutral to save wire.

There are some caveats of course because it is dangerous if wired improperly. Basically the circuits must be on different lines (A, B) so a double pole breaker is required.

Good luck,
Ralph
 
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Old 01-26-19, 09:23 AM
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This isn't correct. The NEC does allow the sharing of a neutral in a multi branch setup under Article 100.

But, this is not a multiwire branch circuit. One circuit is 20 amps with #12 wire and the other circuit is 15 amps with #14 wire.




What he either did not know, or did not care to mention, was that the outlet he pulled the neutral from was on a different circuit.
I am curious how the electrician did this. Did he pull a single white wire or did he pull a cable? I know it's wrong, just wondering what he did.
 
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Old 01-26-19, 12:56 PM
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The NEC does allow the sharing of a neutral in a multi branch setup
Correct. But as Joe pointed out..... this is NOT a MWBC.
 
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Old 01-27-19, 06:18 AM
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Hello,
In an attempt not to hijack a thread; I was simply correcting a general statement that was made...."A neutral, cannot by code, be shared between two circuits...." which is incorrect. There was no distinction or clarification offered. It was just a general statement.

It's already been stated that the sharing of a neutral is not permitted in the OP's case but it is allowed in other instances under the NEC. I simply wanted to clarify that.

God Bless,
Ralph
 
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