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GFCI or AFCI operation #196546
10/12/10 02:40 PM
10/12/10 02:40 PM
Niko  Offline OP
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Will a GFCI or AFCI circuit breaker trip if it only sees a return current on the neutral that is from another circuit due to crossed neutrals in a Jbox.

For example, the GFCI circuit feeds bathroom receptacles but does not have any load on it, however the neutral of this circuit has been crossed with a non protected circuit in the same junction box, with out any load on the GFCI will it trip if it sees a return current on the neutral that is from another circuit?

Thanks


Be kind to your neighbor, he knows where you live

Work Gear for Electricians and the Trades
Re: GFCI or AFCI operation [Re: Niko] #196549
10/12/10 03:42 PM
10/12/10 03:42 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
Yes it will trip.

In fact one of the the most common source of mystery AFCI trips is a short from neutral to ground, essentially the same thing. You have some phase current going out that is not matched by the neutral current coming back.


Greg Fretwell
Re: GFCI or AFCI operation [Re: gfretwell] #196551
10/12/10 04:26 PM
10/12/10 04:26 PM
Niko  Offline OP
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Greg, i agree with you 100% on what you said.

but in this hypothetical situation there is no phase current going out. there is only return current coming back from another circuit.


Be kind to your neighbor, he knows where you live

Re: GFCI or AFCI operation [Re: Niko] #196552
10/12/10 05:09 PM
10/12/10 05:09 PM
L
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
Quote
You have some phase current going out that is not matched by the neutral current coming back.


Zero going out, and non zero coming back. Trip.

Zero going out, zero coming back. NO trip.

Non zero going out. SAME non zero coming back. NO trip.

Non zero going out, different coming back. TRIP

Re: GFCI or AFCI operation [Re: LarryC] #196553
10/12/10 05:25 PM
10/12/10 05:25 PM
Niko  Offline OP
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Got it thanks a lot.

good explanation i will use it.


Be kind to your neighbor, he knows where you live

Re: GFCI or AFCI operation [Re: Niko] #196558
10/13/10 02:27 AM
10/13/10 02:27 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
A GFCI is really a pretty simple device. There is a small transformer in there (sensing coil) with the "hot" wound one way(top pair of green wires) and the "neutral" wound the other way (bottom pair of green wires. That is the primary. If the current is exactly the same they cancel, there is no flux in the core and the secondary winding has zero volts. Any difference shows up as a secondary voltage and the device trips.

[Linked Image]

Last edited by gfretwell; 10/13/10 02:31 AM.

Greg Fretwell
Re: GFCI or AFCI operation [Re: gfretwell] #196561
10/13/10 01:57 PM
10/13/10 01:57 PM
Niko  Offline OP
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Very cool, thanks Greg.


Be kind to your neighbor, he knows where you live


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