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#14447 - 09/23/02 05:15 AM GFCI & grounding
rowd Offline
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Registered: 09/13/02
Posts: 31
Loc: Park Forest, Illinois, USA
"A GFCI is not dependent of a ground to function. It does not measure shorts to the ground, it measures the current difference between the hot and neutral wires. A sudden difference of 5 ma. or more, indicating that there is another path for the electricity to flow through will trip this device."

I have heard that a GFI can be wired so that it still works without a ground. Is this true? Every time I install one without a ground, it acts like a ordinary receptacle and the GFI does not trip when shorted to ground.
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#14448 - 09/23/02 05:53 AM Re: GFCI & grounding
resqcapt19 Offline
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Registered: 11/10/00
Posts: 2209
Loc: IL
It will work just fine when installed without an equipment grounding conductor. How did you test it?
Don
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#14449 - 09/23/02 07:07 AM Re: GFCI & grounding
pauluk Offline
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Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Yes, it's true. The GFI breaker in a panel doesn't have a ground connection run to it. A GFI receptacle's ground terminal connects only to the yoke and the grounding contact, not to the GFI electronics.

If you fit a GFCI on an old 2-wire ungrounded circuit, then the reason the GFI doesn't trip when you use a plug-in tester is that the ground pin on the receptacle isn't actually grounded. If you ran a circuit from the receptacle hot to a grounded object, then it will trip.
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#14450 - 09/23/02 08:51 AM Re: GFCI & grounding
jdevlin Offline
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Registered: 08/07/02
Posts: 402
Loc: welland ontario canada
Of course it won't work when shorted to ground. The ground is open. You are not shorting to anything.
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#14451 - 09/23/02 03:59 PM Re: GFCI & grounding
sparky66wv Offline
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Registered: 11/17/00
Posts: 2342
Loc: West Virginia
Don't be tempted to run a jumper from neutral to the ground screw on the GFCI either... This would allow the tester to work, but would in reality, create a potentially dangerous situation.

I've seen this done many times.
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#14452 - 09/23/02 04:07 PM Re: GFCI & grounding
rowd Offline
Member
Registered: 09/13/02
Posts: 31
Loc: Park Forest, Illinois, USA
resqcapt19

In answer to your question....I would use a GFI tester.....the red plug-in type and if there is no ground present it does not trip the GFI.
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#14453 - 09/26/02 04:00 PM Re: GFCI & grounding
motor-T Offline
Member
Registered: 11/10/01
Posts: 293
Loc: Girard, Ohio, USA
rowd
Try using a 'Wiggy' type tester from the hot side of the receptacle to a grounded surface, it should trip without a problem.

Mark
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#14454 - 09/26/02 04:48 PM Re: GFCI & grounding
resqcapt19 Offline
Member
Registered: 11/10/00
Posts: 2209
Loc: IL
rowd,
A plug in tester will not test a GFCI that is installed without an EGC. That tester works by placing a resistor between the hot and ground. If there is no ground, then there will be no current flow and the GFCI will not trip. Just use the test button on the GFCI. It works by placing a resistor between the line side hot and the load side neutral. It doesn't need the EGC to function. There is no need to use any type of external tester to test GFCI receptacles.
Don
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#14455 - 09/27/02 12:30 PM Re: GFCI & grounding
motor-T Offline
Member
Registered: 11/10/01
Posts: 293
Loc: Girard, Ohio, USA
Don
Are saying my method will not work ? Using the test button is fine, but for insurance I always try to test it under a somewhat real condition.

Mark
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#14456 - 09/27/02 12:49 PM Re: GFCI & grounding
pauluk Offline
Member
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Mark,

The test button on the GFI itself tests the electronics and trip circuitry just as effectively as applying an external hot to ground connection.

All the test button does is unbalanced the hot & neutral currents through the sensing xfmr by connecting load-side hot to line-side neutral via a suitable resistance.

About the only way that you could have the test button trip the GFI while a 6mA external fault would not, would be if the test resistor went low in value and at the same time the GFI lost sensitivity. Not likely!
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