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In my bathroom, there is a GFIC outlet at the vanity. This outlet then feeds a switch that controls a fan that is directly over the shower. The light over the sink is also protected by this GFIC. Everything works okay except that occasionally when the fan is turned off, the GFIC trips. The GFIC has never tripped when the fan has been turned on. Turning the sink lights on and off, or even the lights in the fan enclosure do not cause this to happen. I have replaced the GFIC and it still happens. Replacing the switch also did not solve the problem. I assume that when the fan is turned off, there must be some type of spike that occurs and causes the GFIC to trip. I worked over 30 years in the auto industry and we sometimes had to install resistor/capacitor or other devices to "snub" noise when inductive loads like large motor contactors were turned off. Do you think this would help? Another option would be to use a double pole wall switch for the fan which would disconnect both of the current carrying conductors, leaving only the ground conductor connected. Has anyone else run into this annoying problem?

Perry
 

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retired framer
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In my bathroom, there is a GFIC outlet at the vanity. This outlet then feeds a switch that controls a fan that is directly over the shower. The light over the sink is also protected by this GFIC. Everything works okay except that occasionally when the fan is turned off, the GFIC trips. The GFIC has never tripped when the fan has been turned on. Turning the sink lights on and off, or even the lights in the fan enclosure do not cause this to happen. I have replaced the GFIC and it still happens. Replacing the switch also did not solve the problem. I assume that when the fan is turned off, there must be some type of spike that occurs and causes the GFIC to trip. I worked over 30 years in the auto industry and we sometimes had to install resistor/capacitor or other devices to "snub" noise when inductive loads like large motor contactors were turned off. Do you think this would help? Another option would be to use a double pole wall switch for the fan which would disconnect both of the current carrying conductors, leaving only the ground conductor connected. Has anyone else run into this annoying problem?

Perry
The gfci is reading the difference between power and neutral and when a change is registered, it trips. Neutral often has voltage when measured from neutral to ground. That power is unused by something else in the house and the gfci picks up the change when that something else is turned off or on.
 

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Discussion Starter #4
CodeMatters -- I am in Ohio, NEC is code used in my location. Manufacturer (NuTone/Brone) states in literature that came with fan that GFIC is needed if fan is "above bath or shower". Seems like a good idea since lights in fan assembly would require either standing in tub (which hopefully is empty) or changing bulbs from ladder and dangling off ladder centerline to reach bulbs in fan. If I remember right, the fan and light have separate neutral and hot connections, but share a single ground wire.

NealTW -- After reading your reply, I tried a test. I turned off every other circuit but the bathroom circuit at the breaker box. I disconnected everything from the bathroom circuit but the fan (all lights off at the switch, nothing plugged into the GFIC outlet). I turned the fan on and off on about a 30 second cycle. On the eighth try, the GFIC opened when the fan was turned off. After another 14 tries, the same thing happened. I think this pretty much indicates that the trouble is coming from the fan, and since the GFIC only pops off when the fan is turned off, I must assume that it is some sort of regenerated power. (By the way, I love the Fraser Valley.)

I have been poking around some other internet sites, and one suggested that I should not only change the GFIC but use a different brand, since some are more sensitive to regenerated power. They also stated that the use of a double pole switch would not help. Several posts stated these as facts. The consensus is to use a specification grade GFIC as opposed to a bargain-basement Big Box store GFIC. They stated that while the ground fault protection requirements are set by law, and all manufacturers must meet these requirements, the more expensive GFIC's will have additional filters and circuits to make them more noise resistant. I remember when GFI breakers were first sold and some tripped if you looked at them wrong, while others were much more forgiving. I can understand how this could be the case. I will try an upscale GFIC outlet and report the results.
 

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some reactive loads like motors,
will produce a back EMF spike when turned off,
your GFCI is probably picking this up.
you could try the double pole switch idea ?
Or try running the fan thru a small 1 to 1 isolation transformer,
hopefully the inductance of the tranny will dampen the back EMF spike.
:glasses:
 

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The gfci is reading the difference between power and neutral and when a change is registered, it trips. Neutral often has voltage when measured from neutral to ground. That power is unused by something else in the house and the gfci picks up the change when that something else is turned off or on.


No. GFCIs are fairly simple. They use a differential transformer to measure the difference in CURRENT between the neutral and hot line. If current is leaking somewhere the neutral and hot will not be equal and the differential transformer will show it and the gfci will trip.

So back emf or strange turn on or turn off transients shouldn’t trip a GFCI because the current is flowing equally.

I have heard of cases where the cable after the GFCI is very long there can be some capacitive effects of the hot wire to ground which can cause a leakage to ground but it’s only on really long runs >75’. It sounds like your GFCI is within short distance of the fan so this seems unlikely.












Sent from my iPad using Tapatalk
 

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retired framer
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No. GFCIs are fairly simple. They use a differential transformer to measure the difference in CURRENT between the neutral and hot line. If current is leaking somewhere the neutral and hot will not be equal and the differential transformer will show it and the gfci will trip.

So back emf or strange turn on or turn off transients shouldn’t trip a GFCI because the current is flowing equally.

I have heard of cases where the cable after the GFCI is very long there can be some capacitive effects of the hot wire to ground which can cause a leakage to ground but it’s only on really long runs >75’. It sounds like your GFCI is within short distance of the fan so this seems unlikely.

Sent from my iPad using Tapatalk
I think now I was thinking of the neutral when two circuit are sharing the same neutral. :wink2:
 
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