GFCI weirdness

nap

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Be careful, if that modified shredder ever causes a fire, and the inspectors figure out it was modified, you may be in for some home insurance surprise.
 

nap

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Originally Posted By: SHOZ
I've also seen GFCIs trip if pushed into too small of a box. It must distort the frame of them.
Some models can also be permanently damaged by overtightening the terminal screws. Apparently a printed circuit board inside the device would crack.
 

JHZR2

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There are fluorescent lights on the circuit that has the GFCI trip. Apparently they can cause nuisance trips. Perhaps the dehumidifier, though widely separated, causes just enough distortion that then the GFCI observes something abnormal when the fluorescent has its start pulse.
 
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Was it modified? All PC traces, printed graphics, and holes called for that line filter. Problem was that a required part got 'forgotten'. Meanwhile, fire was not going to happen. Been doing this design thing for too many generations. Read the rest. The shredder worked without tripping the GFCI so often for so many years that its gears finally wore out. Shredder was recently replaces - apparently with one that was not redesigned by a business school graduate. IOW the new one came from Asia - where they teach people how things work rather than how to increase profits.
 
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Dehumidifier must not generate a start pulse - if properly manufactured. We have traced fluorescent lamp trips to wires leaking current into the safety grounded frame. So GFCI did exactly what it is suppose to do. Is a GFCI defective? I built a GFCI tester. An adjustable resistor in the 20K region that can cause a leakage current from a few milliamps to 10 milliamps. It even located a defective item that was only leaking just under 3 milliamps most of the time. And therefore causing intermittent GFCI trips. Nuisance trips are only speculation - created by using correlation to make a conclusion - and without numbers. Nuisance trips are really traceable to something that is contantly defective - and intermittent - such as that paper shredder. No intermittent GFCI was found. Either a GFCI was completely failed or tester tripped it everytime at something near to 5 milliamps. These things are so reliable that 'reason from trips' should always start elsewhere. Even if the lamp and dehumidifier are 100 feet apart and still on the same circuit breaker, then are (electrically) same as if 3 feet apart.
 
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2,169
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Saskatchewan, Canada
Originally Posted By: nap
Be careful, if that modified shredder ever causes a fire, and the inspectors figure out it was modified, you may be in for some home insurance surprise.
So I've been told, many times. Problem is, I can't find a single documented case where a non-UL listed device led to an insurance problem (which is a much worse case than a modified UL-listed device, which describes the shredder in the example). Nor does the US NEC require UL-listed devices exclusively. Nor can I find a clause in my insurance policy that specifies only approved, unmodified electrical appliances can be connected to the household AC outlets. Note that the UL is not a government regulatory agency. Until I do, I consider it an urban myth. Back to the OP's problem. The GFCI receptacle, which if the first receptacle on a line, and is properly wired (you can screw this up) should protect all downstream outlets, remember, looks for Ground Faults. The most common Ground Fault (and one that will trip a breaker or blow a fuse at the panel, no GFCI required) is when the hot (black) AC wire contacts either the ground wire or a grounded item ... outlet, cover, or internally in an appliance. GFCI devices take that quite a bit further. They will of course trip under the above conditions. However they will also trip when there is resistance on the ground line, perhaps due to corrosion or a loose ground connection. They should trip at 20~30 mA (which is not very much current differential) and depending on the duration, can trip when detecting as little as 6 mA differential current. By "differential" we are referring to how GFCIs work ... they measure what should be on the line and what actually is on the line, and if the difference is above a certain threshold, they trip. You can easily check the operation of a GFCI by putting an incandescent lamp (turned on) on a downward outlet and pressing the "test" button. The lamp should go out. If it does, the GFCI unit is working as it should, and GFCI unit itself is not the problem.
 
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An ideal GFI would react only to ground faults on its load side. If it reacts to surges, noise, or voltage dips, it is defective.
 
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Originally Posted By: nap
Originally Posted By: SHOZ
I've also seen GFCIs trip if pushed into too small of a box. It must distort the frame of them.
Some models can also be permanently damaged by overtightening the terminal screws. Apparently a printed circuit board inside the device would crack.
I recently had a freshly installed GFCI trip without any load on it. It would trip when I tightened the mounting screws fully. I applied insulation tape over the terminals to ensure they were not making contact with the metal box and it did not help. It was a very tight fit into a small box - rework box, mounted with F brackets. I also like to tighten the terminals screws very tightly to avoid future loose contacts. So it looks like one of the two factors mentioned above (tight fit/ over tightened terminal screws) is causing the issues in my installation. This was at a customer's house, at the end of a long day. I left the mounting screws a little loose. I have been back at the customer's house since then and the GFCI has not tripped. I have to go back to the customer's house this week for another job and will replace the GFCI and mount it in a different box to avoid a potential call back on my job.
 
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Electrical code now requires GFCI for sump pump outlet. New house, GFCI for sump pump occasionally tripped, maybe once every couple of months. One day it tripped, I didn't notice until the walk-up basement stairwell had 2" of standing water in it. I reset GFCI and later replaced it with one that has an alarm that will sound when it trips. The replacement has never tripped and it's been at least 6 months since I installed it. I think there are differences in how the different brands of GFCIs are immune to nuisance tripping. By the way, when that basement stairwell has 2" of water in it, there is a LOT of water in the foundation drains. The sump pump ran continuously for almost 30 minutes to get rid of it all.
 
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JHZR2

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Originally Posted By: westom
Dehumidifier must not generate a start pulse - if properly manufactured. .... Even if the lamp and dehumidifier are 100 feet apart and still on the same circuit breaker, then are (electrically) same as if 3 feet apart.
Dehumidifier is a Santa Fe; a well-established brand/model. They are NOT on the same breaker. Dehumidifier is even split onto a separate sub panel. Closest that could be said is maybe the same half of the split phase in the main panel.
 
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Connecticut, USA
Originally Posted By: brianl703
Electrical code now requires GFCI for sump pump outlet. New house, GFCI for sump pump occasionally tripped, maybe once every couple of months. One day it tripped, I didn't notice until the walk-up basement stairwell had 2" of standing water in it. I reset GFCI and later replaced it with one that has an alarm that will sound when it trips. The replacement has never tripped and it's been at least 6 months since I installed it. I think there are differences in how the different brands of GFCIs are immune to nuisance tripping. By the way, when that basement stairwell has 2" of water in it, there is a LOT of water in the foundation drains. The sump pump ran continuously for almost 30 minutes to get rid of it all.
Same happened to me.... switched the circuit over to a regular one and haven't had a problem since.
 
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Originally Posted By: bmwpowere36m3
Same happened to me.... switched the circuit over to a regular one and haven't had a problem since.
A classic and irresponsible example of curing symptoms. That GFCI was reporting a serious human safety issue. So we killed the messenger - removed a GFCI. Left the threat to human life in place. And then played mind games to justify that change.
 
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Originally Posted By: westom
A classic and irresponsible example of curing symptoms. That GFCI was reporting a serious human safety issue. So we killed the messenger - removed a GFCI. Left the threat to human life in place. And then played mind games to justify that change.
GFCIs can trip for reasons that have absolutely nothing to do with a ground fault. In every case where I had a GFCI that tripped for no apparent cause, I replaced it with another one and that resolved the problem. The rationale, incidentally, behind the requirement that sump pumps be on a GFCI is that someone might use the sump pump receptacle to power other loads. A hardwired sump pump, if such a thing exists, would not be required to be on a GFCI. Did those who pushed the code requirement that sump pump outlets be GFCI ever consider how much of a human safety issue is it when a basement floods because the sump pump GFCI nuisance-trips and nobody deals with it before that GFCI and other electrical equipment in the basement is submerged in water?
 
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Originally Posted By: brianl703
Did those who pushed the code requirement that sump pump outlets be GFCI ever consider how much of a human safety issue is it when a basement floods because the sump pump GFCI nuisance-trips ...
When one does not know how to fix a problem, then one invents "nuisance-trips". Every trip has an electrical reason why. That reason why is a greatest threat exists when skin can get wet. Sump pump, that was only rumored to be good, was leaking current in a dangerous manner. A GFCI reported that defect. Unfortunately some electricians do not even know how to solve this. So they say that GFCI is not necessary. Then the homeowner pays for a solution that solved nothing. Then a homeowner does not know some electricians do not and need not know how electricity works. Electricians are only required to know what must connect to what. Code only teaches what is required for human safety - not how electricity works. The GFCI is reporting a defect. The naive invent an excuse called "nuisance tripping". The informed consumer first finds and then later fixes that defect. GFCI is reporting a human safety issue. Solve the problem - not its symptoms. And yes. Every time I was involved, a nuisance trip was always traced to some defect. Every time.
 
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I can make a GFCI trip just by keying up a radio transmitter next to it. The fact is, GFCIs are built to be CHEAP and can and do trip due to induced current on the wires from external sources (lightning, radio transmitters), movement (yes, a GFCI can trip due to mechanical shock or torsion/twisting of it's body--seen that more than a few times), problems with the electronic circuitry inside (resistors/capacitors change value due to (1) component aging and (2) not being very high quality parts to start with), exposure to outdoor conditions (even when installed with a weatherproof cover--GFCIs installed outdoors seem to die an early death, indicated by tripping without being able to be reset). Note that I am talking about GFCI RECEPTACLES. I would expect GFCI breakers to be a higher-quality product. But they are rarely used because they cost more and are not as convenient to reset.
 
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ca
Originally Posted By: brianl703
I can make a GFCI trip just by keying up a radio transmitter next to it.
Good. Symptom has been described. Now define the anomaly. Define the defect - electrical current paths - that forced that GFCI to trip. The informed will then fix a defect that causes a symptom. How did you first identify and later fix what is clearly a defect?
 
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Why bother? I'm not the one who engineered the RFI (radio frequency interference) susceptible GFCI. I cannot correct the internal design flaw that causes a particular GFCI to trip in the presence of a strong RF signal. There are three solutions to the problem: 1)Replace the GFCI with another one that may, hopefully, be better engineered such that it won't trip due to RFI. 2)Remove sources of RFI from the immediate environment of the GFCI (either by relocating the GFCI or the source of RFI) 3)Do away with the GFCI entirely.
 
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ca
Originally Posted By: brianl703
Why bother?
That is the entire point. One has no idea how this electricity works. Solution is to even violate well proven and required codes for human safety - to justify ignorance. The OP requested replies from the fewer who actually know this stuff. An informed answer would define a current from that transmitter, through a perfectly good GFCI, that is tripping that GFCI. Rationalization, using wild speculation and subjective reasaoning, also invents "nuisance tripping" myth. GFCI is reporting a defect. GFCI for a sump pump trips because a defect exists. Solve the problem; never cure symptoms. Where does a defect more likely exist? In the transmitter.
 
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