GFCI Tripping Repeatedly?

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re: the NEC doesn't require GFCI protection for the fan unless it's located over the tub, and the manufacturer requires it
I'm not pushing back...just trying to understand the wording above.
The "and" in that sentence seems to indicate that the manufacturer has the final say. In other words, the NEC requirement is based on 2 criteria: location and the manufacturer's requirement.
Are there fans that can be installed above a tub but not require a GFCI protection because the manufacturer doesn't require one?
Thanks
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The NEC requirement is just the general one that equipment be installed according to manufacturer's requirements. Manufacturers typically say that their fans may be installed over showers if they are installed on a GFCI. I don't know if there are any that allow installation over a shower without GFCI protection.
Cheers, Wayne
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Wayne Whitney wrote:

A good description of manufacturer's requirements being mandatory, not optional.
There are also requirements from the agency approving the device. That is usually UL. Those requirements are also mandatory.
Bath fans and GFCIs came up about a month ago: From the UL "White Book" "Fans intended to be mounted over tubs or showers have been evaluated for such purposes and are marked 'Acceptable for use over a bathtub or shower when installed in a GFCI protected branch circuit."
The manufacturer will always require GFCI protection for a fan over a tub. If the manufacturer misses it, it is required by UL. [Old fans may have been made when the UL standard was different.]
(The UL "White book" is available at: http://www.ul.com/regulators/2006WhiteBook.pdf 5.5M and not real easy to use)
The "final say" may be NEC, manufacturer, or approval agency.
--
bud--

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I had this same problem a while back with my bath fan. The problem was a minor leak from the roof vent. Fixed leak. Haven't had this problem since.
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Roger,

My in-laws just had a new roof installed, so I didn't want to cut any holes and risk causing a leak. So we routed the duct out through a sidewall. Except for a short bump up over a beam, the 8' duct slopes mostly towards the outside wall vent.
So, there's no chance of a leak, other than maybe condensation working it's way back. However, the tripping doesn't seem to be related to shower usage, which makes me doubtful of a moisture related cause.
Anthony
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HerHusband wrote:

I am skeptical that a properly working fan should trip a properly working GFCI when the fan is turned off. If there is no ground fault in the fan or switch, there can be no imbalance of currents (conservation of electrons). A double pole switch should not make a difference. I might suggest an intermittent ground fault in the fan or switch when the fan is turned off.
Please let us know what the problem is/was when/if you figure it out.
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Anthony-
Give MQ's theory a try. I would agree with his suggestion that you might have an intermittent ground fault in the switch itself.
Cheap & easy to try it out. Just swap the switch with another SPST from somewhere else in the house.
cheers Bob
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This is incorrect; see an earlier post regarding the collapse of the magnetic field in the motor windings when power is switched off. The consequent backcurrent generated does indeed produce a brief, slight current imbalance. This is evidently of sufficient magnitude and duration to exceed the GFCI's trip threshold.

Of course it should. By opening both the neutral and the hot, a DPST switch prevents the backcurrent from reaching the GFCI, thus preventing the GFCI from ever seeing the imbalance.

Perhaps; but the explanation referenced above is IMO much more likely to be correct.

Very doubtful. Given that it's a single-pole switch, this would require an intermittent, high-resistance short to ground that doesn't draw enough current to make an audible arc. Hard to imagine how that could happen.

Easy enough to test -- but the results are predictable: it won't make any difference.
It's possible that this particular GFCI is a little more sensitive than it should be, and swapping it with a different one may cure the problem.
Switching both the hot and the neutral through a double-pole switch is almost certain to fix it.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

Only if there is leakage to ground. The leakage could be capacitive currents from winding to motor poles. Else, as M Q wrote, how could the current be different in the 2 wires? Field collapse can create a high voltage spike but it creates a current in the circuit through both wires.
Could be high voltage produces current from high side (hot) to grounded motor poles by capacitive current?. Spike is short duration (high frequency) increasing the capacitive current. Size of voltage spike depends on where in the current sine wave the switch opens.

Assuming timing of both poles opening is close enough together that the GFCI doesn't trip.

Yea, seems remote.
--
bud--



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NOT correct. A GFCI trips any time there is an imbalance between the hot and neutral currents, that exceeds the thresholds for duration and current. It is NOT necessary for there to be ANY leakage to ground.

Yes, it does -- and with current reaching the motor through an SPST switch, *one* of those two wires is disconnected from the GFCI when the switch is opened, but the other is not. And that's why the GFCI sees an imbalance -- and why I think a DPST switch will eliminate the problem.

Possible, I suppose... but I'm not convinced.

Pretty good assumption, I'd say.
--
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Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

>>>

>> Only if there is leakage to ground.

Of course. But how do you get a different current in the wires of a bath fan without ground leakage.

Still not explained - how is the current not the same in both wires unless there is some form of leakage to ground. The current is the same in both wires for a light bulb. Why not the fan.

>

Wall switches generally operate slowly - apparently intentionally. (You can typically move the handle to a position that causes the contacts to arc - not that arcing is relevant.) I have read the intent is that the contact break be slow enough to reduce inductive kick from magnetic field collapse. GFCIs may operate in 1/2 cycle. It is not obvious to me that slow operation and random variation would not result in timing difference between poles of 1/2 cycle in some switches.
--
bud--



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As noted above, see an earlier post in this thread (not mine) regarding magnetic field collapse and back-EMF.

As noted above, see an earlier post in this thread, etc.

Because a light bulb is a resistive load, and a fan is an inductive load, at least in part.
--
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Doug Miller (alphageek at milmac dot com)
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check and see if the positve(black) and neg(white) wires are connected to the coresponding black and white wires in the fan, if they are reversed u will trip a gfci
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snipped-for-privacy@gmail.com wrote:

You want to explain why you think that's the case?
--
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Doug Miller (alphageek at milmac dot com)
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Well, it was worth a try, but the DPST switch did not fix the problem either. It worked fine for about two weeks, then tripped again a couple of days ago.
As always, it trips when the fan switch is turned "OFF", not while it is running.
I've tried two different GFCI's, and three different switches, and they all have the same results.
I'm baffled. The wiring is new and in good condition. The only two things I can think are the fan itself is bad, or condensation is draining back into the fan and causing problems.
Still, it seems like the DPST switch would completely isolate the fan from the GFCI. There shouldn't be any current flow even if there was a problem with the fan. And there have been absolutely no problems while it is running. Only when it is turned off.
Other than rewiring to take the fan off the GFCI, or replacing the fan, are there any other things I could try?
Anthony
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Please describe how you wired the DPST switch; post a diagram if possible.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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As you would expect. The incoming hot wire goes to one pole of the switch, the incoming neutral wire goes to the other pole. Then the switched hot and neutral go directly to the fan.
The ground wire is directly tied to all other grounds.
The switch clearly indicates which two terminals are the "line" and which two terminals are the "load". Outgoing hot wire is on the same pole as the incoming hot wire, and the outgoing neutral is on the same pole as the incoming neutral.
I don't see any other way you could wire the switch?
Anthony
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If it's *still* causing the GFCI to trip, then I see only two possibilities: 1) the original GFCI *and* the replacement are defective 2) there is a ground fault in the fan itself.
--
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Doug Miller (alphageek at milmac dot com)
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Doug,

Seems unlikely. I've never had a GFCI fail before, so I can't imagine two being bad, especially since they are two different brands.

That seems to be the only thing remaining, though I don't understand how it could trip the GFCI if the DPST switch cuts it out of the circuit completely?
I wired the two bathrooms in our house the exact same way and we've never had a problem with the fans tripping the GFCI's.
Anthony
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Oh, I agree, it's very unlikely. Still possible, though...

Ground and neutral wired together at some point in the circuit?
--
Regards,
Doug Miller (alphageek at milmac dot com)
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