We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now, but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

HerHusband wrote:

We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now, but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony
Hi,
Probably motor body and fan enclosure does not have or have poor ground?

On Dec 24, 7:30 am, HerHusband wrote:
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now, but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, when the fan
is turned off, the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The GFI senses this slight current as mismatch between hot & neutral
currents & trios.

cheers
Bob

On 2007-12-24, BobK207 wrote:

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, when the fan
is turned off, the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The GFI senses this slight current as mismatch between hot & neutral
currents & trios.

Hi Bob,

If this is the story, what is the proper way to deal with this? Is
there a type of motor that can be specified and which would minimize
this effect? Would it be acceptable practice to switch both the
neutral and hot to the motor? If so do double pole switches break
both connections sufficiently close to simultaneously to avoid the
induced current imbalance?

Thanks, Wayne

"HerHusband" wrote in message
...
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent
fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now,
but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side
wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.


The fan isn't required to be on a GFI protected circuit unless it is in the
shower/tub space. I'm not sure what could be causing your problem. Maybe
try installing a two pole switch so that the hot and the neutral are being
disconnected at the same time.

"HerHusband" wrote in message
...
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent
fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now,
but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side
wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

Why connect the fan to the GFI at all? Is it a requirement in your
locality?

This is not an uncommon anomaly. As others have said, the NEC doesn't
require GFCI protection for the fan unless it's located over the tub, and
the manufacturer requires it



"HerHusband" wrote in message
...
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent
fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now,
but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side
wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

On Dec 24, 10:30*am, HerHusband wrote:
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now, but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side wall)..
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

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.

On Dec 24, 11:34 am, "HeyBub" wrote:
BobK207 wrote:

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, when the fan
is turned off, the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The field collapses 60 times a second when running...

yeah but BOTH the hot & the neutral are still connected when the fan
is running.....

I believe it is the "collapse" with the hot open & the neutral still
connected that causes the problem for the GFI current sensing circuit.

My comments were meant to provide a plausible reason for the behavior
"GFI trip on fan shutdown"

& your theory is?

Sounds like Doug's comment that its ok to switch both should solve the
issue.


OP-

Is the fan / switch wiring such that you can easily install a DPST
switch and switch the hot & the neutral to the fan?

cheers
Bob

I have had trouble with motor loads tripping GFI's.
The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I was afraid of something like that. At this point, there's not much I can
do to rewire the fan to be off the GFCI.

Is the fan / switch wiring such that you can easily install a DPST
switch and switch the hot & the neutral to the fan?

Yes, I could install a DPST, but I can't say I've seen them in stores? Then
again, I've never really been looking for them.

Anthony

This is not an uncommon anomaly. As others have said, the NEC doesn't
require GFCI protection for the fan unless it's located over the tub,
and the manufacturer requires it

Well, good to know, but a little too late. It had been my understanding
that the entire bathroom circuit needed to be protected by the GFCI. But
the inspector mentioned a couple of things that didn't need to be on it
also. Oh well, no harm done, except for the fan nuisance.

The DPST switch idea sounds like my best option if I can find one.

Anthony

Roger,

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.

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

On Dec 25, 9:08 am, HerHusband wrote:
I have had trouble with motor loads tripping GFI's.
The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I was afraid of something like that. At this point, there's not much I can
do to rewire the fan to be off the GFCI.

Is the fan / switch wiring such that you can easily install a DPST
switch and switch the hot & the neutral to the fan?

Yes, I could install a DPST, but I can't say I've seen them in stores? Then
again, I've never really been looking for them.

Anthony

Anthony-

If you have a Home Depot near by, they probably have the DPST

here's a link to listing of the Leviton double pole products (white),
HD (at least in my area) stocks Leviton products

http://www.leviton.com/OA_HTML/xxlcf...20&st=kw&cpg=0

the 1202-2W switch looks to be the one you'd want.

The DPST solution will only work IF the neutral to the fan comes from
the switch box & can be safely broken there.


cheers
Bob

Bob,

Thanks for the info!

If you have a Home Depot near by, they probably have the DPST

We have a couple of HD's and a Lowes nearby. I'll have a look next time I'm
there. I've never had a need for them before, so I've probably looked over
them and didn't know it.

The DPST solution will only work IF the neutral to the fan comes from
the switch box & can be safely broken there.

Yep, the power comes into the 3-gang switch box, then separate cables run
to the fans and lights. It'll be no problem switching to the DPST switch.

I'll have to wait and see if changing the switch will prevent the GFCI from
tripping when the fan is turned off, but it's a relatively simple and
inexpensive thing to try. Thanks for the tip.

Anthony

On Mon, 24 Dec 2007 16:23:28 GMT, Wayne Whitney
wrote:

Hi Bob,

If this is the story, what is the proper way to deal with this? Is
there a type of motor that can be specified and which would minimize
this effect? Would it be acceptable practice to switch both the
neutral and hot to the motor? If so do double pole switches break
both connections sufficiently close to simultaneously to avoid the
induced current imbalance?

Thanks, Wayne


An easy "try this" will be to swap out the washroom fan with a new one
or one from another bathroom. The puzzling thing is the exhaust fan
motor draws so little power that even stopping the motor by hand
should not cause any circuit hiccups (and will not cause the motor to
overheat.)

"HerHusband" wrote in message
...
Bob,

Thanks for the info!

If you have a Home Depot near by, they probably have the DPST

We have a couple of HD's and a Lowes nearby. I'll have a look next time
I'm
there. I've never had a need for them before, so I've probably looked over
them and didn't know it.

The DPST solution will only work IF the neutral to the fan comes from
the switch box & can be safely broken there.

Yep, the power comes into the 3-gang switch box, then separate cables run
to the fans and lights. It'll be no problem switching to the DPST switch.

I'll have to wait and see if changing the switch will prevent the GFCI
from
tripping when the fan is turned off, but it's a relatively simple and
inexpensive thing to try. Thanks for the tip.



If the GFCI is in the same three gang box as the switch for the fan and
lights you should be able to reconfigure the wiring to eliminate the light
and fan from the GFCI protection.

HerHusband wrote:
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now, but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

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.

HerHusband wrote:

Bob,

Thanks for the info!


If you have a Home Depot near by, they probably have the DPST


We have a couple of HD's and a Lowes nearby. I'll have a look next time I'm
there. I've never had a need for them before, so I've probably looked over
them and didn't know it.


The DPST solution will only work IF the neutral to the fan comes from
the switch box & can be safely broken there.


Yep, the power comes into the 3-gang switch box, then separate cables run
to the fans and lights. It'll be no problem switching to the DPST switch.

I'll have to wait and see if changing the switch will prevent the GFCI from
tripping when the fan is turned off, but it's a relatively simple and
inexpensive thing to try. Thanks for the tip.

Anthony

I think you'll be shocked at what they charge for a DPST.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

On Dec 26, 1:06 pm, M Q wrote:
HerHusband wrote:
We recently remodeled my in-laws bathroom and, as per code, the entire 20
amp bathroom circuit is protected by a 20A GFCI outlet. Everything was
inspected and functions as it should.

Unfortunately, the GFCI is tripping occasionally when the bathroom vent fan
is turned "off". It never trips when turning on the fan, only when turning
it off. And, it may go a few weeks before it trips, and then suddenly trip
three times in a row. Then it'll work fine again for a few weeks.

I suspected a bad GFCI, so I replaced it with a new one, and also replaced
the switch that controls the fan. It doesn't seem to trip as often now, but
it tripped for me again last night when we were visiting.

The only remaining item seems to be the fan itself, but I'm curious if
there's some other possible cause I might be overlooking? The fan has been
installed for a few months now, so I probably can't return it at this
point.

I thought maybe condensation from moisture draining back through the vent
pipe (it had to be routed up over a beam to get out through the side wall).
But, the tripping doesn't really seem to be related to when the shower was
used recently.

Thoughts?

Anthony

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.


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

In article , BobK207 wrote:
On Dec 26, 1:06 pm, M Q wrote:
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).

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.

A double pole switch should not make a difference.

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.

I might suggest an intermittent ground fault in the
fan or switch when the fan is turned off.

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

Please let us know what the problem is/was when/if you figure it out.

Give MQ's theory a try. I would agree with his suggestion that you
might have an intermittent ground fault in the switch itself.

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.

Cheap & easy to try it out. Just swap the switch with another SPST
from somewhere else in the house.

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)

It's time to throw all their damned tea in the harbor again.

If the GFCI is in the same three gang box as the switch for the fan
and lights you should be able to reconfigure the wiring to eliminate
the light and fan from the GFCI protection.

No, the GFCI is in a different box on a different wall. Power comes from
the GFCI over to the 3-gang box, then three cables exit the switch box to
go to the fixtures (ceiling lights, vanity lights, bath fan).

There wouldn't be an easy way to take the fan off the GFCI.

I wired both bathrooms in our own house the same way, with the fan on the
GFCI, and we've never had a GFCI trip. So it has been odd that my in-laws
GFCI trips so often with the same wiring scheme.

Anthony

you might have an intermittent ground fault in the switch itself.
Just swap the switch with another SPST from somewhere else

As I mentioned in my original post, I already replaced the switch and GFCI
with new ones, thinking the switch was bad or the GFCI was faulty. It
seemed to reduce the tripping slightly, but did not eliminate it.

Replacing the fan is kind of my last resort.

Anthony

Doug Miller wrote:
In article , BobK207 wrote:
On Dec 26, 1:06 pm, M Q wrote:
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).

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.

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.


A double pole switch should not make a difference.

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.

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


I might suggest an intermittent ground fault in the
fan or switch when the fan is turned off.

Perhaps; but the explanation referenced above is IMO much more likely to be
correct.
Please let us know what the problem is/was when/if you figure it out.
Give MQ's theory a try. I would agree with his suggestion that you
might have an intermittent ground fault in the switch itself.

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.

Yea, seems remote.

--
bud--

In article , bud-- wrote:
Doug Miller wrote:
In article
, BobK207
wrote:
On Dec 26, 1:06 pm, M Q wrote:
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).

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.

Only if there is leakage to ground.

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.

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.

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.

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.

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


A double pole switch should not make a difference.

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.

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

Pretty good assumption, I'd say.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

"HerHusband" wrote in message
...
If the GFCI is in the same three gang box as the switch for the fan
and lights you should be able to reconfigure the wiring to eliminate
the light and fan from the GFCI protection.

No, the GFCI is in a different box on a different wall. Power comes from
the GFCI over to the 3-gang box, then three cables exit the switch box to
go to the fixtures (ceiling lights, vanity lights, bath fan).

There wouldn't be an easy way to take the fan off the GFCI.

Sure there would. Just disconnect the cable coming from the load side of the
GFCI outlet, and connect it to the line side . There is no need to connect
any of the loads you have through a gfci





I wired both bathrooms in our own house the same way, with the fan on the
GFCI, and we've never had a GFCI trip. So it has been odd that my in-laws
GFCI trips so often with the same wiring scheme.

Anthony

RBM wrote:
"HerHusband" wrote in message
...
If the GFCI is in the same three gang box as the switch for the fan
and lights you should be able to reconfigure the wiring to eliminate
the light and fan from the GFCI protection.
No, the GFCI is in a different box on a different wall. Power comes from
the GFCI over to the 3-gang box, then three cables exit the switch box to
go to the fixtures (ceiling lights, vanity lights, bath fan).

There wouldn't be an easy way to take the fan off the GFCI.

Sure there would. Just disconnect the cable coming from the load side of the
GFCI outlet, and connect it to the line side . There is no need to connect
any of the loads you have through a gfci




I wired both bathrooms in our own house the same way, with the fan on the
GFCI, and we've never had a GFCI trip. So it has been odd that my in-laws
GFCI trips so often with the same wiring scheme.

Anthony

Some exhaust fans are specifically listed to be installed with a GFCI
protected supply. The concern is that the vibration of the fan is more
likely to cause a fault and a person who is standing in a shower is
particularly vulnerable to electric shock. Removing the GFCI protection
from the shower fan may be a violation of the electric code requirement
for installing all devices in conformity with the instructions included
in the listing or labeling.

You can purchase a combination device that has the switch and a GFCI on
the same yoke and use that to control the fan. It would make a lot more
sense however to open the neutral splice in the three gang box and test
for a ground fault on each of the cables that are not the supply. The
one that shows a measurable resistance to ground from the load side of
the switch with the switch open and the neutral splices open is the one
that is ground faulted. If you cannot get the fault to read a
measurable resistance with the circuits thus disconnected from the
supply you can either open and inspect all three load outlets for a
pinched wire or an over tightened cable clamp or you can rent an
insulation tester and subject the three cable's insulated conductors to
three hundred volts. Insulation testers give the resistance of the
conductors insulation under a specific test voltage. If you use any
higher setting than three hundred volts you are likely to cause faults
rather than locate the existing fault.
--
Tom Horne

Doug Miller wrote:
In article , bud-- wrote:
Doug Miller wrote:
In article
, BobK207
wrote:
On Dec 26, 1:06 pm, M Q wrote:
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).


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.

Only if there is leakage to ground.

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.

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

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.

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.

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.

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.

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

A double pole switch should not make a difference.
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.

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

Pretty good assumption, I'd say.

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--

On Dec 24, 2:34*pm, "HeyBub" wrote:
BobK207 wrote:

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, *when the fan
is turned off, *the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The field collapses 60 times a second when running...

120 times per second

"Tom Horne" wrote in message
news:6XXcj.13589$1q4.5129@trnddc06...
RBM wrote:
"HerHusband" wrote in message
...
If the GFCI is in the same three gang box as the switch for the fan
and lights you should be able to reconfigure the wiring to eliminate
the light and fan from the GFCI protection.
No, the GFCI is in a different box on a different wall. Power comes from
the GFCI over to the 3-gang box, then three cables exit the switch box
to
go to the fixtures (ceiling lights, vanity lights, bath fan).

There wouldn't be an easy way to take the fan off the GFCI.

Sure there would. Just disconnect the cable coming from the load side of
the GFCI outlet, and connect it to the line side . There is no need to
connect any of the loads you have through a gfci




I wired both bathrooms in our own house the same way, with the fan on
the
GFCI, and we've never had a GFCI trip. So it has been odd that my
in-laws
GFCI trips so often with the same wiring scheme.

Anthony

Some exhaust fans are specifically listed to be installed with a GFCI
protected supply. The concern is that the vibration of the fan is more
likely to cause a fault and a person who is standing in a shower is
particularly vulnerable to electric shock. Removing the GFCI protection
from the shower fan may be a violation of the electric code requirement
for installing all devices in conformity with the instructions included in
the listing or labeling.

In his case, the fan is not located over the shower or tub



You can purchase a combination device that has the switch and a GFCI on
the same yoke and use that to control the fan. It would make a lot more
sense however to open the neutral splice in the three gang box and test
for a ground fault on each of the cables that are not the supply. The one
that shows a measurable resistance to ground from the load side of the
switch with the switch open and the neutral splices open is the one that
is ground faulted. If you cannot get the fault to read a measurable
resistance with the circuits thus disconnected from the supply you can
either open and inspect all three load outlets for a pinched wire or an
over tightened cable clamp or you can rent an insulation tester and
subject the three cable's insulated conductors to three hundred volts.
Insulation testers give the resistance of the conductors insulation under
a specific test voltage. If you use any higher setting than three hundred
volts you are likely to cause faults rather than locate the existing
fault.
--
Tom Horne

In article , bud-- wrote:
Doug Miller wrote:
In article , bud--
wrote:
Doug Miller wrote:
In article
, BobK207
wrote:
On Dec 26, 1:06 pm, M Q wrote:
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).


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.

Only if there is leakage to ground.

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.

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

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

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.

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.

Still not explained - how is the current not the same in both wires
unless there is some form of leakage to ground.

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

The current is the same
in both wires for a light bulb. Why not the fan.

Because a light bulb is a resistive load, and a fan is an inductive load, at
least in part.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

In article , Terry wrote:
On Dec 24, 2:34=A0pm, "HeyBub" wrote:
BobK207 wrote:

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, =A0when the fan
is turned off, =A0the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The field collapses 60 times a second when running...

120 times per second

Whether it collapses 60, 120, or a thousand times a second when running is not
relevant, because when the fan is running, both wires are connected to the
GFCI. With power to the fan routed through a single-pole switch so that only
the hot conductor is opened by the switch, only *one* wire is connected to the
GFCI, thus making it possible for the collapsing field to cause imbalanced hot
and neutral currents at the GFCI.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

On Dec 28, 9:14*pm, (Doug Miller) wrote:
In article , Terry wrote:





On Dec 24, 2:34=A0pm, "HeyBub" wrote:
BobK207 wrote:

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, =A0when the fan
is turned off, =A0the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The field collapses 60 times a second when running...

120 times per second

Whether it collapses 60, 120, or a thousand times a second when running is not
relevant, because when the fan is running, both wires are connected to the
GFCI. With power to the fan routed through a single-pole switch so that only
the hot conductor is opened by the switch, only *one* wire is connected to the
GFCI, thus making it possible for the collapsing field to cause imbalanced hot
and neutral currents at the GFCI.



With only "one" wire connected to the GFI there is no difference of
potential either. It kind of makes induced currents impossible too,
but run with it.

Want to bet on the double pole switch?

In article , Terry wrote:
On Dec 28, 9:14=A0pm, (Doug Miller) wrote:

Whether it collapses 60, 120, or a thousand times a second when running is not
relevant, because when the fan is running, both wires are connected to the
GFCI. With power to the fan routed through a single-pole switch so that only
the hot conductor is opened by the switch, only *one* wire is connected to the
GFCI, thus making it possible for the collapsing field to cause imbalanced hot
and neutral currents at the GFCI.

With only "one" wire connected to the GFI there is no difference of
potential either. It kind of makes induced currents impossible too,
but run with it.

Maybe you ought to spend a little more time thinking about that...

Want to bet on the double pole switch?

Sure.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Whether it collapses 60, 120, or a thousand times a second when
running is not relevant, because when the fan is running, both wires
are connected to the GFCI. With power to the fan routed through a
single-pole switch so that only the hot conductor is opened by the
switch, only *one* wire is connected to the GFCI, thus making it
possible for the collapsing field to cause imbalanced hot and
neutral currents at the GFCI.

With only "one" wire connected to the GFI there is no difference of
potential either. It kind of makes induced currents impossible too,
but run with it.

Maybe you ought to spend a little more time thinking about that...

Want to bet on the double pole switch?

Sure.

I have to admit, I'm a little skeptical about the double-pole switch.
Whether resistive or inductive, how can you have current flow unless the
circuit is completed? Open the hot wire and current shouldn't flow through
the neutral either, unless there really was a fault in the wiring
somewhere? I was an electronic tech MANY years ago, so maybe I've just been
away from this stuff too long.

In any case, my own attempts at solving the problem have failed, so I'm
willing to give it a try. I bought a double-pole switch yesterday ($9) and
plan to install it in the next day or two. Unfortunately, due to the
erratic nature of the problem, I may not know for a month or more whether
it solved the tripping problem. But, if it does trip again, at least I can
rule out the switch once and for all.

Thanks for the feedback!

Anthony

On Dec 27, 11:22*am, bud-- wrote:
Doug Miller wrote:
In article , BobK207 wrote:
On Dec 26, 1:06 pm, M Q wrote:
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).

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.

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.



A double pole switch should not make a difference.

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.

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



I might suggest an intermittent ground fault in the
fan or switch when the fan is turned off.

Perhaps; but the explanation referenced above is IMO much more likely to be
correct.
Please let us know what the problem is/was when/if you figure it out.
Give MQ's theory a try. * I would agree with his suggestion that you
might have an intermittent ground fault in the switch itself.

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.

Yea, seems remote.

--
bud--

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

In article , HerHusband wrote:
Whether it collapses 60, 120, or a thousand times a second when
running is not relevant, because when the fan is running, both wires
are connected to the GFCI. With power to the fan routed through a
single-pole switch so that only the hot conductor is opened by the
switch, only *one* wire is connected to the GFCI, thus making it
possible for the collapsing field to cause imbalanced hot and
neutral currents at the GFCI.

With only "one" wire connected to the GFI there is no difference of
potential either. It kind of makes induced currents impossible too,
but run with it.

Maybe you ought to spend a little more time thinking about that...

Want to bet on the double pole switch?

Sure.

I have to admit, I'm a little skeptical about the double-pole switch.

So test it.

Whether resistive or inductive, how can you have current flow unless the
circuit is completed?

Back-EMF can flow through the neutral wire because the neutral is connected to
ground at the breaker box.

Open the hot wire and current shouldn't flow through
the neutral either, unless there really was a fault in the wiring
somewhere?

Back-EMF from the collapsing magnetic field in the motor windings when it's
switched off.

I was an electronic tech MANY years ago, so maybe I've just been
away from this stuff too long.

In any case, my own attempts at solving the problem have failed, so I'm
willing to give it a try. I bought a double-pole switch yesterday ($9) and
plan to install it in the next day or two. Unfortunately, due to the
erratic nature of the problem, I may not know for a month or more whether
it solved the tripping problem. But, if it does trip again, at least I can
rule out the switch once and for all.

Yep. Let us know what happens.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

In article , wrote:

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

You want to explain why you think that's the case?

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Doug Miller wrote:
In article , HerHusband wrote:


Whether resistive or inductive, how can you have current flow unless the
circuit is completed?

Back-EMF can flow through the neutral wire because the neutral is connected to
ground at the breaker box.

Open the hot wire and current shouldn't flow through
the neutral either, unless there really was a fault in the wiring
somewhere?

Back-EMF from the collapsing magnetic field in the motor windings when it's
switched off.


You basically have a 2 wire inductor. You are saying that when the
circuit is broken, magnetic field collapse produces a current flow in
one wire that is not equal to the current flow in the other wire. You
may be in line for a Nobel Prize. Or maybe not.

--
bud--

T. Rex wrote:

In article ,
says...

Doug Miller wrote:

In article , HerHusband wrote:

Whether resistive or inductive, how can you have current flow unless the
circuit is completed?

Back-EMF can flow through the neutral wire because the neutral is connected to
ground at the breaker box.


Open the hot wire and current shouldn't flow through
the neutral either, unless there really was a fault in the wiring
somewhere?

Back-EMF from the collapsing magnetic field in the motor windings when it's
switched off.


You basically have a 2 wire inductor. You are saying that when the
circuit is broken, magnetic field collapse produces a current flow in
one wire that is not equal to the current flow in the other wire. You
may be in line for a Nobel Prize. Or maybe not.



Pay attention this time. The currents _at_the_GFCI_ are unequal, because
one of the two wires is not connected to the GFCI.

I think that YOU need to pay attention:
In the wire that is not connected we can agree that the current is zero?
In the wire that is connected, what do you think the current is?
If it is zero, they are equal and the GFCI should not trip.
If it is not zero, where do you think that current is going?
Those electrons have to go (come from) somewhere. They are not
getting stored in the fan. They could be going to ground, but
only if you have a ground fault.

In article 6cRdj.559$jX4.196@trnddc07, M Q wrote:
In the wire that is not connected we can agree that the current is zero?

Of course.

In the wire that is connected, what do you think the current is?

Small, but non-zero.

If it is zero, they are equal and the GFCI should not trip.

Correct.

If it is not zero, where do you think that current is going?

To ground, obviously, at the service entrance.

Those electrons have to go (come from) somewhere. They are not
getting stored in the fan.

Electric current is the movement of electric *charge*. The current is
generated by the collapsing magnetic field.

They could be going to ground,

True.

but only if you have a ground fault.

False. All current in the neutral wire ultimately goes to ground at the
service panel.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.