Cause for GFCI mA trip on floor heating thermostat

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Tell us everything, the things we'd see if we were there and looking for ideas.

Breaker (which?) or faceless GCFI? How soon does it trip?

Brand of floor heating and t-stat.

And, as mentioned, how did you test your wiring?
 
GFCI tripping

GFCI tripping

Tested with Megohmmeter.
Standard breaker
Dual Conductor twisted pair heating element. (Rather not mention company name)
Thermostat - 5 mA Touch screen, 120V/240V
I think it might be from the neutral source coming into the house.
Thermostat's at times will trip randomly and can be reset.
 
Tony Ledford said:
What would cause a GFCI trip on a floor heating thermostat when the cable tests fine? (resistance, continuity, and insulation test all pass)
Click to expand...

is the heating cable embedded in concrete?

I doubt that a resistance or continuity test is going to tell you where 5 mA of stray current went that is tripping the GFCI.

The insulation test might but it also could be that the fault only manifests itself when the heating cable warms up.

I would get an electrician to replace the GFCI that is tripping just in case you have one that is a little flakey. They do go bad from time to time.

But the most likely problem is that the heating cable was either not installed properly or has become damaged since installation.

It could also be that the thermostat is leaking enough current to ground to trip the GFCI. Some of those kind of devices have MOVs or RC networks to ground. It might be enough to cause a GFCI to trip.

is the heating cable and tstat the only thing on that circuit?

Who installed the circuit?

Can the wiring be rearranged so the GFCI is downstream of the tstat to eliminate it as the cause?
 
GFCI mA trip on floor heating thermostat

GFCI mA trip on floor heating thermostat

It seems to cause the nuisance trip when the heating cable warms up, system shuts off and starts back up again. This is typically when tripping occurs.
Heated cable is installed encapsulated in mortar with tile as a surface as are the other 2 bath areas.
The other two do not have this problem. I have tried swapping line voltage from one heated floor to another and the same one still trips.
I am told it could be coming from an outside source, (ie noise interference). This house is a smart home and has all LED lighting.
I have been in the industry for 20 years and this is my first experience with this.
The GFCI is in the thermostat. Same manufacturing date on all 3 thermostats.

 
Tony Ledford said:
It seems to cause the nuisance trip when the heating cable warms up, system shuts off and starts back up again. This is typically when tripping occurs . . . I have tried swapping line voltage from one heated floor to another and the same one still trips . . . The GFCI is in the thermostat. Same manufacturing date on all 3 thermostats.
Click to expand...

Exchange the tripping thermostat with one of the others, and see if the trip behavior stays with the cable or moves with the thermostat.
 
Tony Ledford said:

The GFCI is in the thermostat. Same manufacturing date on all 3 thermostats.
Click to expand...

al hildenbrand said:
Exchange the tripping thermostat with one of the others, and see if the trip behavior stays with the cable or moves with the thermostat.
Click to expand...

I have to agree with Al. Switching the thermostats is the easiest thing to do and will provide the most information.

If it trips a different GFCI in a different thermostat I would be inclined to believe it's a bad cable even if it doesn't show up with a megger test.

Hopefully just a bad thermostat.
 
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