# GFCI trip when ground and neutral touch



## oleguy74 (Aug 23, 2010)

you are on the load side of the gfci.thats what they are supposed to do,how they work.when gnd and neutral touched there is a fault..POP.line side don't matter beacause gnd and nuetral are tied togethet in mai panel.


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## secutanudu (Mar 15, 2009)

Why are you touching the ground wire to the neutral?

Oleguy is right, that is the GFCI operating as it should. There was a ground fault, so it tripped.


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## thewoodguy (Oct 27, 2010)

*Thanks*

That should have been obvious, but thanks for the reminder! Secutanudu, the first was by accident, subsequent were just to figure out what was going on. I feel safe now!


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## Scuba_Dave (Jan 16, 2009)

Is the outlet where you are pulling the ground on the same circuit as the light ?


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## thewoodguy (Oct 27, 2010)

@Scuba-Dave - no, it's separate. The original circuit is ungrounded. I'm still trying to assess the wiring in this place, which was done in 1957. Grounding is spotty, and often run to the nearest copper pipe! Some outlets have a thin ground wire connected to the outside, some don't. It's a mess.


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## oleguy74 (Aug 23, 2010)

be extreamly careful.don't want you hurt...


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## Scuba_Dave (Jan 16, 2009)

thewoodguy said:


> @Scuba-Dave - no, it's separate. The original circuit is ungrounded. I'm still trying to assess the wiring in this place, which was done in 1957. Grounding is spotty, and often run to the nearest copper pipe! Some outlets have a thin ground wire connected to the outside, some don't. It's a mess.


You need to run grounds back to the panel
Not from another circuit
And not to water pipes


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## HVAC_NW (Oct 15, 2007)

GFCI is a differential amplifier. Both neutral and hot are wrapped around in a coil. So, if the inbound and outbound aren't perfectly symmetrical, it sees it as a leak. When you let the neutral touch the ground, the ground wire will act as a parallel jumper back to the panel and some of the current will be diverted and shared with neutral, which causes asymmetry between neutral & hot within the GFCI. So, it will see it as a ground fault.


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## a7ecorsair (Jun 1, 2010)

HVAC_NW said:


> GFCI is a differential amplifier. Both neutral and ground are wrapped around in a coil. So, if the inbound and outbound aren't perfectly symmetrical, it sees it as a leak. When you let the neutral touch the ground, the ground wire will act as a parallel jumper back to the panel and some of the current will be diverted and shared with neutral, which causes asymmetry between neutral & hot within the GFCI. So, it will see it as a ground fault.


GFCI's compare the current in the *Hot* conductor and *Neutral* conductor using a coil. Touching a ground wire to the neutral will cause some of the "return" current to flow in the ground wire and some to flow in the neutral so the GFCI will see an imbalance between the Hot and neutral.


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## HVAC_NW (Oct 15, 2007)

a7ecorsair said:


> GFCI's compare the current in the *Hot* conductor and *Neutral* conductor using a coil. Touching a ground wire to the neutral will cause some of the "return" current to flow in the ground wire and some to flow in the neutral so the GFCI will see an imbalance between the Hot and neutral.


That was a typo. I fixed it. Even with no load, if you short the neutral to ground, it will cause a small amount of current between ground and neutral, which the GFCI will see as asymmetry between hot & neutral, then trip.


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