GFCI Tripping Repeatedly?

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

Reply to
HerHusband
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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?

Reply to
Doug Miller

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

Reply to
DerbyDad03

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

Reply to
Wayne Whitney

I suggested earlier the high voltage spike that can be produced in the fan winding when the switch is turned off could produce capacitive currents from the fan winding the motor poles (ground). The size of the spike depends on where in the sine wave the fan is turned off - random effect. Fans intended to be used on GFCI circuits could be built with more winding isolation. I haven't seen aanswer yet that better fits what happens.

In Mike's description above, if the light is connected across the fan when the fan is turned off the light could absorb part of the spike from the motor winding.

I don't think there is a fix other than "take the fan off the GFCI, or replacing the fan".

Reply to
bud--

If this is true then a bleed off resistor could serve as an incandescent lamp.

This is a total wild ass guess on my part. I would be very interested in knowing if this could work.

Reply to
Terry

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:

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and not real easy to use)

The "final say" may be NEC, manufacturer, or approval agency.

Reply to
bud--

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If, as you suggest, there is a voltage spike when the fan is shut off, and there is more capacitive coupling from one of the fan terminals to ground than the other, then adding a capacitor across the fan leads might reduce that.

Another possibility: I have often seen the armature of motors, when they turn on or off, shift axially. If so, there could be a transient short.

Reply to
M Q

Assume capacitance is equal from both hot and neutral to pole. Leakage also depends on voltage. The neutral end is connected to pole (at the service panel). The voltage from N-to-pole will be minimal. I suspect the winding is constructed so the neutral end is most toward the pole but don't know. Could try reversing the motor H-N leads.

Capacitor across H-N - maybe. The capacitor does not dissipate the energy but may spread it over time and lower the peak voltage. MOV might work but I wouldn't connect one L-N without protection. My guess is a shunt resistance would probably have to be too low value so that it dissipates significant energy.

I wouldn't guarantee trip is from capacitance-spike but it is the best guess I can come up with.

If a supply wire was near an end of the armature - could be.

Reply to
bud--

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Note that GFCIs detect a fault from neutral to ground also. From the schematics I have seen, I believe they do this by inducing a higher frequency common voltage on the the hot and neutral. If there is neutral to ground fault there will be a common mode current of this higher frequency signal which will be detected by the same circuitry and trip.

The point is: don't ignore a ground fault on the neutral side.

Reply to
M Q

Reverse the motor leads in single phase? Doesn't this happen 120 times per second?

Wouldn't an incandescent lamp be a purely resistive load?

Reply to
Terry

If the trip is caused by capacitance to ground and spike, and if the capacitance to motor frame (ground)is lower from the neutral end of the winding than the hot end, reversing the leads may help. I wouldn't bet on it.

Probably not stated previously, a spike is not only high voltage, but because it is short duration it is high frequency. High freq increases capacitive currents.

Another possibility - capacitance from hot wire to ground wire in Romex between fan and GFCI.

Sure. If you don't mind a light turned on with the fan, it works for Mike. May work for the OP.

Reply to
bud--

What I remembered was inducing a current into just the neutral. A manufacturer's datasheet shows common mode induction into both H & N like you said. That would also give "neutral"-ground fault detection if the hot and neutral wires were reversed. The data sheet shows a fullwave rectified 60Hz source, which would be 120Hz with harmonics.

When there is load on a circuit with a GFCI, resistance will cause a voltage from neutral to ground, and there will be current in a N-G fault that will trip the GFCI. With the added circuitry a GFCI will trip on a N-G fault with no load.

(datasheet is at

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Reply to
bud--

According to M Q :

Detecting current difference between hot and neutral is a lot simpler than that.

If the neutral is shorted to the ground, the ground wire acts as a parallel conductor to the neutral which reduces the neutral's current, hence, the hot and neutral won't match.

GFCI's work by running the neutral and ground around a magnetic core, measuring the net magnetic flux, and triggering if it exceeds a certain threshold. If the neutral and hot currents are the same, the magnetic flux cancels out.

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Reply to
Chris Lewis

I see that you didn't even read the link that you provided. "To detect a Neutral to Ground fault there is a second transformer placed upstream of the H-G sense transformer. A small drive signal is injected ... which induces equal voltages on the H and N wires passing through its core."

Reply to
M Q

A typo - neutral and hot instead of neutral and ground.

What is detected by adding the CT in MQ's post is a N-G fault with no load. Without the added CT, the simple GFCI in Chris' post won't detect a N-G fault until there is a load on the circuit. Other than that a GFCI operates as Chris describes.

I was surprised to learn this function was built into GFCIs. But it only adds 2 parts.

Reply to
bud--

Whoops yup.

It seems rather strange even to do that. The slightest bit of load on the circuit, either before or after the GFCI, will mean that the neutral is at a different potential than the ground. If the neutral shorts to the ground after the GFCI, then there will be current flow thru the neutral at the GFCI to the ground without the hot at the GFCI seeing anything.

Me too. I shoulda read a bit farther ;-)

Reply to
Chris Lewis

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