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Old 01-17-2009, 01:49 PM   #1
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GFCI Problem from Hell!


The House we live in is 10 years old.

It has a large Screened room that has been made a permanent part of the house. It appears that the outlets in this area are all done with metal conduit at the 'Baseboard" Level if the aluminum walls of the screen room. There are about a half dozen outlet boxes, on both the inside and outside walls of the screen room, and by supplemental external conduit, run along the lower edge of the concrete outside wall towards the front of the house. The circuit seems to have been added to the circuit that originates in the master bathroom and has a GFI protecting it on the first outlet in the bathroom. The only thing on this circuit is the two outlets in the very large bathroom, and the half dozen outlets outside in and outside the screen porch.

Here is the crazy problem. You can connect a 100 watt lamp to any or all of these outlets and the GFI will not trip. Plug anything in that has a decent load, like our portable hot tub, treadmill or even my Dremel tool running at high speed and the GFI trips instantly.

I have replaced the GFI, upgrading it to 20 Amps from 15 Amps (The breaker on the circuit is 15AMPS and never trips)

This happens if the load is on any of the outlets, including the one in the Master Bath.

I have a small plug in tester that plugs into the outlets and tells me whether they are wired correctly and if they have any shorts, etc. All of the outlets test clean.

There is one outlet on the wall of the Florida room that is on a different Circuit. Any load can be plugged in this circuit, and the load will be handled with no problems. I am not sure if this circuit is protected by a GFI.

I have inspected all the wiring and don't see any problems. HELP!!!

What should i do next?


Last edited by IvanMonet; 01-17-2009 at 01:52 PM.
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Old 01-17-2009, 02:01 PM   #2
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GFCI Problem from Hell!


Do you have a multimeter or an ohm meter?

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Old 01-17-2009, 02:04 PM   #3
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GFCI Problem from Hell!


A simple multi meter would make this much easier to diagnose.
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Old 01-17-2009, 02:16 PM   #4
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GFCI Problem from Hell!


You could have a neutral tied to the ground somewhere. Your 3-light tester will never know the difference, but the GFCI would.

Remove power from the circuit at the panel;
Remove and inspect each and every receptacle and anything else that is on this circuit.
You should not have any of the white wires/silver screws on the receptacles touching or connected to any of the ground screws, metal boxes, etc.

Also, if you don't find a problem at any of the receptacles, remove the wires from the LOAD terminals of the GFCI in the bathroom, then re-apply power to the circuit.
Plug one of the loads that caused the GFCI to trip, and see what happens.
If it does not trip, then your problem is somewhere between the bathroom and the screened room. Perhaps there is a neutral touching the conduit somewhere.

One more point: Changing your GFCI from 15A to 20A does absolutely nothing, except violate code. Not a safety issue at all, but they just don't want anyone trying to plug a 20A device into a 15A branch and causing the breaker to trip all the time.
You are not permitted to have a 20A receptacle on a 15A branch, but you can have a 15A receptacle on a 20A branch, as long as it is not a single receptacle (not a duplex).
A GFCI is not an over-current device. It will trip only when there is a ground-fault.
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Old 01-17-2009, 02:54 PM   #5
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GFCI Problem from Hell!


Pass 10A into the neutral and measure the millivolt drop from the neutral or the ground terminal to a known good ground picked up elsewhere.

This assumes the neutral and ground conductor are both #12. You should see 16 mV for every foot the outlet is distant from the panel, if the connection is at the panel where it should be.

If the spurious connection is at your end, you'd see 8mV/foot, two #12's in parallel.

To get a true 4-terminal Kelvin measurement necessary for measuring very low resistances the leads that inject the 10A should not touch the leads you use to measure the voltage. This, because sometimes contact impedance is as high as conductor resistance.

If your meter won't read that low you can use a doorbell xformer as a step-up xformer, but you'll need to measure exactly what step-up ratio you're getting in this case.
Do not connect your xformer low voltage winding across 120v unless you fuse it first! 1/16A should be about right for this application.

Last edited by Yoyizit; 01-17-2009 at 02:56 PM.
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Old 01-17-2009, 03:35 PM   #6
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Quote:
Originally Posted by Yoyizit View Post
Pass 10A into the neutral and measure the millivolt drop from the neutral or the ground terminal to a known good ground picked up elsewhere.

This assumes the neutral and ground conductor are both #12. You should see 16 mV for every foot the outlet is distant from the panel, if the connection is at the panel where it should be.

If the spurious connection is at your end, you'd see 8mV/foot, two #12's in parallel.

To get a true 4-terminal Kelvin measurement necessary for measuring very low resistances the leads that inject the 10A should not touch the leads you use to measure the voltage. This, because sometimes contact impedance is as high as conductor resistance.

If your meter won't read that low you can use a doorbell xformer as a step-up xformer, but you'll need to measure exactly what step-up ratio you're getting in this case.
Do not connect your xformer low voltage winding across 120v unless you fuse it first! 1/16A should be about right for this application.
hey man; I think you're being too technical for a DIY. The guy is probably not an engineer, as you are.
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Old 01-17-2009, 03:56 PM   #7
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GFCI Problem from Hell!


I would disconnect the wiring at the load side of the GFCI just as KE2KB has said, including the ground that passes through. Then on the outside outlets you will have to disconect the grounds on the outlets and the neutrals. Using the ohm setting on your meter check from neutral to ground at each, also check from neutral to the box and conduit. If you see a OL reading your good. If you get an ohm reading then I would start with that conduit. Only Do This Once You Shut Off The Power!
Does the lamp your plugging in have a ground prong?
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Old 01-17-2009, 05:11 PM   #8
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Originally Posted by KE2KB View Post
hey man; I think you're being too technical for a DIY. The guy is probably not an engineer, as you are.
Yeah, 10A can only carry you so far. . .

Chris75 may be right about GFCIs; not all nuisance tripping is nuisance tripping, not if it's consistent.
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Old 01-17-2009, 05:43 PM   #9
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Originally Posted by Yoyizit View Post

Chris75 may be right about GFCIs; not all nuisance tripping is nuisance tripping, not if it's consistent.
I would never lie to you. Personally, I would just megger the circuit and replace the bad wiring.
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Old 01-17-2009, 05:55 PM   #10
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I would never lie to you. Personally, I would just megger the circuit and replace the bad wiring.
False statements are not the same as lies. . .I'm reasonably sure you believe what you say.

"It aint what you don't know what gets you into trouble, it's what you know for sure that aint so!"
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Old 01-17-2009, 06:51 PM   #11
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False statements are not the same as lies. . .I'm reasonably sure you believe what you say.

"It aint what you don't know what gets you into trouble, it's what you know for sure that aint so!"
I've never run across a nuisance tripping problem where I could not find the culprit, so until that day, nuisance tripping is just a term used by the untrained.
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Old 01-17-2009, 07:07 PM   #12
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I've never run across a nuisance tripping problem where I could not find the culprit, so until that day, nuisance tripping is just a term used by the untrained.

Nuisance tripping?

I agree, there is always something wrong when the gfci trips, they trip for a reason!

I have never had a "nuisance tripping problem"
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Old 01-17-2009, 07:13 PM   #13
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Nuisance tripping?

I agree, there is always something wrong when the gfci trips, they trip for a reason!

I have never had a "nuisance tripping problem"
yep... my biggest pet peeve is when someone suggest they just remove the problematic GFCI...
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Old 01-17-2009, 08:58 PM   #14
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GFCI Problem from Hell!


I've only had GFIs trip without an actual fault in two instances.

1) Golf course fountain. The fountain was located about 700' from the maintenance building. They wanted a GFI breaker in the building. I advised against a breaker, use a GFI receptacle instead. The GFI breaker would trip right away, it was proved good (5 MA test), all 3 conductors were meggered at 1000 volts, less that 1 microamp of leakage. Current on the circuit with conductors capped off at the load end; 13 milliamps. Very likely due to capacitive coupling in long wires, but never proved.

2) Reflected power from distorted waveforms. Like VFDs, or any other switching-type power conversion. I don't think you can predict when this will fool the GFI, a lot of factors have to 'line up' to cause a problem. This one had me baffled until I connected current clamps from both conductors to a dual-trace oscilloscope, and found that the two waveforms didn't exactly match all the time.

Other than the above, I've always found the cause of a GFI tripping. Motor starting current, capacitor charge, transformer inrush, etc.; none of these will cause a GFI to trip without an actual fault.

Rob
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Old 01-17-2009, 09:08 PM   #15
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I've only had GFIs trip without an actual fault in two instances.

1) Golf course fountain. The fountain was located about 700' from the maintenance building. They wanted a GFI breaker in the building. I advised against a breaker, use a GFI receptacle instead. The GFI breaker would trip right away, it was proved good (5 MA test), all 3 conductors were meggered at 1000 volts, less that 1 microamp of leakage. Current on the circuit with conductors capped off at the load end; 13 milliamps. Very likely due to capacitive coupling in long wires, but never proved.

2) Reflected power from distorted waveforms. Like VFDs, or any other switching-type power conversion. I don't think you can predict when this will fool the GFI, a lot of factors have to 'line up' to cause a problem. This one had me baffled until I connected current clamps from both conductors to a dual-trace oscilloscope, and found that the two waveforms didn't exactly match all the time.

Other than the above, I've always found the cause of a GFI tripping. Motor starting current, capacitor charge, transformer inrush, etc.; none of these will cause a GFI to trip without an actual fault.

Rob
So, what do you do about motor starting, etc that causes a GFCI to trip?
I'm wondering what I should do if I have to deal with this kind of issue when I install the GFCI for my washer. There has never been one before, but I have decided that I want the protection.

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