Why does this pop the GFI?

[GerryB]

A detached gararge new wiring, I have one circuit. I fed a receptacle, GFI. From the load side I ran a cable to an outside plug, another to a switch box. From the switch box to another plug. The switch is a 3-way where I carried the feed and neutral through from the other end. I had all the neutrals spliced together and the gfi would pop. When I spliced the neutrals separately(plug to plug, light to light) which I usually do if it's two different circuits, it was ok.

 

[templdl]

Pease assure that the GFI is being feed with a neutral and a ground that are not bonded together other than at the service entrance.
Then, please assure that the neutral and grounding conductors are insulated and isolated on the load side of the GFI.
Should there be a question regarding the integrity of the load side circuit, remove any connected load, turn off the breaker feeding that circuit, remove the neutral and grounding conductors from the load side of the GFI and take an ohm meter and measure the resistance across the neutral and ground (EGC) conductors. You result should show an infinite resistance, that is an open circuit which is what should eb expected. Any resistance reading at all will indicate that current has the capability of flowing between the neutral and the EGC which will with almost all certainty trip the GFI.
If it checks out as an open circuit then proceed to the items that are connected down stream. Measuring the neutral to EGC resistance should result in an open circuit as it should be. If not further inspection is required to determine the cause.

 

[GerryB]

Thanks for that reply. I did not bother checking for continuity between ground and neutral except physically in the boxes I was in. Many times that is the problem and that could still be in the box on the other end of the 3-way. I guess my question was if it is all the same circuit and there is no bonding between ground and neutral would the fact that the load side neutral from the gfi is spliced to the same circuit neutral that is not off the load side be the cause?

 

[templdl]

Thanks for that reply. I did not bother checking for continuity between ground and neutral except physically in the boxes I was in. Many times that is the problem and that could still be in the box on the other end of the 3-way. I guess my question was if it is all the same circuit and there is no bonding between ground and neutral would the fact that the load side neutral from the gfi is spliced to the same circuit neutral that is not off the load side be the cause?

You might have a point and that could be the issue. The neutral on the load side of a GFI, GFCI, of as a matter of fact an AFCI is to be treated as sacred ground. That neutral must be insulated and isolated from the EGC and it must be dedicated to the circuit being served. Should you connect the neutral in a way that the neutral current is allowed to return to the source other than through the GFI the GFI will not see only part of not even any of the neutral current. As such the GFI will respond as there being a ground fault. Remember that a GFI protects by measuring the current going to the load against the current returning from the load. It's looking for an imbalance which it will interpret as a ground fault.

 

[tom baker]

A GFCI will trip on a line to ground and neutral to ground. When GFCIs were first being installed, there was a lot of nuisance tripping, due to a neutral to ground connection in a box. There probably were a lot of GFCIs replaced.

 

[jxofaltrds]

A detached gararge new wiring, I have one circuit. I fed a receptacle, GFI. From the load side I ran a cable to an outside plug, another to a switch box. From the switch box to another plug. The switch is a 3-way where I carried the feed and neutral through from the other end. I had all the neutrals spliced together and the gfi would pop. When I spliced the neutrals separately(plug to plug, light to light) which I usually do if it's two different circuits, it was ok.

Confused! if you only have one circuit how can you seperate 'neutrals'?

 

[eprice]

A detached gararge new wiring, I have one circuit. I fed a receptacle, GFI. From the load side I ran a cable to an outside plug, another to a switch box. From the switch box to another plug. The switch is a 3-way where I carried the feed and neutral through from the other end. I had all the neutrals spliced together and the gfi would pop. When I spliced the neutrals separately(plug to plug, light to light) which I usually do if it's two different circuits, it was ok.

When you say "all of the neutrals spliced together", do you mean some of the neutrals are from a portion of the circuit before the GFCI and some of them from a portion that is after the GFCI? All of the current that flows through the GFCI on the ungrounded conductor must return through the the GFCI on the neutral conductor. If some of the neutral current has a path back to the source that bypasses the GFCI, the GFCI will trip.

 

[templdl]

When you say "all of the neutrals spliced together", do you mean some of the neutrals are from a portion of the circuit before the GFCI and some of them from a portion that is after the GFCI? All of the current that flows through the GFCI on the ungrounded conductor must return through the the GFCI on the neutral conductor. If some of the neutral current has a path back to the source that bypasses the GFCI, the GFCI will trip.

Yes, point made in my previous post.