GFCI Tripping Repeatedly?

Page 4 of 4  
wrote:

I have a similar problem. I noted that when the light bulb on the fan fixture is illuminated the problem does not occur. Perhaps a resistive load across the fan absorbs any power line spikes which trip the GFCI. Just an idea.
Mike
Note: my return address contains no numeric characters.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

In my case, the fan is just a fan. No light or heater in it.
Wiring is about as simple as it gets. A single incoming 12/2 cable coming from the switch. Fan housing is grounded, hot and neutral are connected according to the fan instructions (black to black, white to white. No brainer).
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mike Hennessey wrote:

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".
--
bud--


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bud-- wrote:

...
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
M Q wrote:

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.
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bud-- wrote:
...

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
M Q wrote:

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 http://cache.national.com/ds/LM/LM1851.pdf
--
bud--

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
http://www.codecheck.com/gfci_principal.htm
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Chris Lewis wrote:

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."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
M Q wrote:

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.
--
bud--



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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 ;-)
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Terry wrote:

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.
--
bud--


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How quickly after you turn off the swich does the GFCI trip, and how long does it take for the fan to fully spin down?

I can't really think of any. Sorry.
Cheers, Wayne
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Instantly as far as I can tell. Flip the switch off and the GFCI trips at the same time.

I don't know. Probably a couple of seconds at least.
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.