rewiring 40 year old house. replacing 2 slot receptacles with 3 slots. placing a gfi at first receptacle in circuit. problem with 3 ways to kitchen ceiling light. a hot was run to one of 3 ways but with no neutral. neutral was picked up at light from another circuit. apparently this worked just fine before i got there. but with a gfi as first receptacle in circuit, the 3 ways will trip gfi. what difference does using neutral from another circuit make? i disconnected hot from circuit it was originally on and connected it to circuit that neutral from light was on. it worked fine then.
how does neutral (grounded conductor) really work?
- Thread starter ronson
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tonyi
Senior Member
Re: how does neutral (grounded conductor) really work?
In a GFCI, the neutral and hot are compared for current flow and they need to be within ~5ma of each other or the device trips.
By grabbing another branch's neutral, the GFCI will now sense a (very large) imbalance because the neutral current for the light is no longer returning through the GFCI. In effect, this sort of situation is a hardwired & guaranteed trip. FWIW, an AFCI breaker on this light branch would also trip in similar manner.
In a GFCI, the neutral and hot are compared for current flow and they need to be within ~5ma of each other or the device trips.
By grabbing another branch's neutral, the GFCI will now sense a (very large) imbalance because the neutral current for the light is no longer returning through the GFCI. In effect, this sort of situation is a hardwired & guaranteed trip. FWIW, an AFCI breaker on this light branch would also trip in similar manner.
- Location
- Massachusetts
Re: how does neutral (grounded conductor) really work?
Ronson you can't beat Tony's concise description of why you where having trouble.
Here is a graphic and link that get into more detail if you are interested.
How GFCIs Work
Ronson you can't beat Tony's concise description of why you where having trouble.
Here is a graphic and link that get into more detail if you are interested.
How GFCIs Work
Re: how does neutral (grounded conductor) really work?
tony & bob, thanks for your help. please see my new questions regarding this problem in the contracting & estimating section. (this is reason why i couldn't find my original post because i placed it in this grounding section and forgot what section i put it in.)
tony & bob, thanks for your help. please see my new questions regarding this problem in the contracting & estimating section. (this is reason why i couldn't find my original post because i placed it in this grounding section and forgot what section i put it in.)
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