I was troubleshooting a kitchen countertop GFCI that would not hold the load. After opening all countertop locations involved and finding no reason for the GFCI to be tripping I turned on the garbage disposal and the GFCI tripped. I verified the garbage disposal was on its own circuit and the neutral wires were not joined. At this point I believed the garbage disposal was the cause. I began making up all the locations I had accessed and began cleaning up. The GFCI tripped again. I realized the furnace had just kicked on. Now I am really at a loss. Furnace has a separate circuit also. Has anyone experienced anything like this? Any suggestions as to the cause?
Stumped
- Thread starter cawireman
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synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Are the garage disposal and the furnace on the opposite phase from that supplying the GFCI receptacle? If so then perhaps the following could be occurring. If there's excess resistance upstream of the panel's neutral bar, then the surge of current when the motors start would produce a spike of higher L-N voltage on the line side of the GFCI. Perhaps this could then cause the GFCI to trip if the voltage feeding it momentarily exceeds its design capability.
To check out the possibility of excess resistance in the neutral, you could put a substantial load like a portable heater on a branch circuit and see if it has a signifcantly larger effect on L-N voltages in the panel than would be expected.
To check out the possibility of excess resistance in the neutral, you could put a substantial load like a portable heater on a branch circuit and see if it has a signifcantly larger effect on L-N voltages in the panel than would be expected.
ptonsparky
Tom
- Occupation
- EC - retired
New installation or existing?
Has it ever worked?
Has it ever worked?
hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
Might check voltages in the panel, possibly the main neutral starting to fail. Main outside, sub panel inside? Should be zero volts between neutral and ground bar in panel if so.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Just started the ignition process or was it when blower motor kicked on, which is usually after plenum gets warmed up?
Inductive kickback can sometimes effect GFCI's even if not on same circuit, but that normally something that happens when opening a circuit with an inductive load. Bad control in furnace possibly could be causing some "chatter" to make it happen when starting?
Just looking at this from a theory/fundamentals understanding, without the aid of years of experience, I would suggest that the issue has to be on the downstream side of the GFCI.
Not discounting the years experience of other members; It seems like it's irrelevent what is happening up stream because the GFCI will only trip if the ungrounded conducter and the grounded conductor do not balance.
I would suggest looking for a hidden connection of the neutral of the GFCI's circuit with a different circuit Downstream of the GFCI, or a neutral ground connection Downstream of the GFCI.
But first replace the GFCI with a new one to rule out a faulty GFCI
Or it could be that the GFCI is doing its job and there is an appliance that is faulting
Not discounting the years experience of other members; It seems like it's irrelevent what is happening up stream because the GFCI will only trip if the ungrounded conducter and the grounded conductor do not balance.
I would suggest looking for a hidden connection of the neutral of the GFCI's circuit with a different circuit Downstream of the GFCI, or a neutral ground connection Downstream of the GFCI.
But first replace the GFCI with a new one to rule out a faulty GFCI
Or it could be that the GFCI is doing its job and there is an appliance that is faulting
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Terminator5047
Senior Member
- Location
- Saint Louis
- Occupation
- Electrician
unhook the dishwasher could be a bad board and see if problem persists
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Normally GFCI's only respond to current issues "downstream". They will however be triggered at times by upstream disturbances usually a transient voltage of some sort or by RF interference.
ptonsparky
Tom
- Occupation
- EC - retired
Does the GFCI trip at the start or stop of either appliance and putting in a new GFCI, sometimes a different brand, is a very good starting point.
The answer to Existing or New, may prevent us from playing '50 Questions'.
The answer to Existing or New, may prevent us from playing '50 Questions'.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
The thing is, GFCI’s are electronic devices, during normal operation, load side problems can cause a trip, but faulty power on the input side can also cause issues. The most common is lightning surges, does not have to be close to trip a gfci. So all sides of the equation need to be looked at. A mistap will cause a trip condition when any load is applied, where a faulty appliance trip will depend on the type of fault, intermittent or maintained. Since it is tripping when unrelated loads are activated, the common point between them would be a neutral connection. It may not be the problem, but it is an easy check to start with.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
What is a "mistap"?
I see no way that there could be a lightning strike nearby at the exact time that a load turns on every time that load turns on. The chances of that happening are remote.
I also don't see how a bad connection upstream could be responsible.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Mistap is where they tied the load neutral to another circuit neutral, or the load hot to another neutral that is not from the gfci. The lightning strike is just an example of a non load side trip. It is not what is happening in the op’s post.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I am pretty sure I have not heard that called a mistap before.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
It is the abbreviated version of “incorrectly tapped” or mis-tapped.
ptonsparky
Tom
- Occupation
- EC - retired
I hadn't either, but still understood what he meant. (Figured it was an autocorrect)
Existing. Condition began 2 weeks ago.
Yes
Trips when the blower kicks on.
At the start
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