Oven trips GFCI

[augie47]

This has been an "over the phone" troubleshoot question and I can't figure what I am overlooking,........
New restaurant... 240v steamer oven, cord & plug(no neutral) on a GFCI.
Sit the oven on a 120v grounded cooler and the oven GFCI trips.
Isolate the oven on a mat and GFCI does not trip. Measure no voltage from oven case to ground; use a jumper wire from case to ground an no trip.
Electrician may be leaving out some vital info but other than that can you think of a reason the GF would trip ?

 

[synchro]

When the oven is on a mat, I suggest having the voltage between the oven case and the cooler case be measured.
Also, does a jumper wire between the two cases cause the GFCI to trip? (just to check whether it's only an electrical connection between the cases causing the trip and not something more subtle).

Measure no voltage from oven case to ground; use a jumper wire from case to ground an no trip.

Was the ground mentioned here from the oven receptacle, or from somewhere else?

 

[Little Bill]

I would say since it is a new oven that there might be moisture in the internal wiring compartment from being on a ship. But since the oven works on a mat that probably rules that out. Be worth a try to let it run/heat while on the mat to dry any possible moisture out. Then try it at it's resting place.

 

[Tulsa Electrician]

Both circuits from the same panel and system?

 

[augie47]

Both circuits from the same panel and system?

yes

 

[hbiss]

Apparently, the case and line cord ground are not connected internally. Start by measuring resistance from the case to each hot and ground pin on the plug. Should be infinite (no resistance) from the hots and zero resistance from the ground pin.

You don't have to turn it on for the GFCI to trip, right? Just sit it on the cooler and plug it in?

-Hal

 

[winnie]

Some random thoughts:

1) High impedance fault though oven elements to ground, but at the element midpoint. No imbalance current and no GFCI trip from oven alone, even when frame touches ground.

2) When other EC said 'jumper to ground case, no trip' was the jumper to some random metal on the ground or to a known good bonded EGC?

3) Is the voltage from the chassis of the cooler to ground?

-Jon

 

[kwired]

This has been an "over the phone" troubleshoot question and I can't figure what I am overlooking,........
New restaurant... 240v steamer oven, cord & plug(no neutral) on a GFCI.
Sit the oven on a 120v grounded cooler and the oven GFCI trips.
Isolate the oven on a mat and GFCI does not trip. Measure no voltage from oven case to ground; use a jumper wire from case to ground an no trip.
Electrician may be leaving out some vital info but other than that can you think of a reason the GF would trip ?

Is EGC to oven connected to EGC/grounded conductor at panel or did it happen to get connected to GFCI load neutral terminal?

Could happen if someone happened to use a 10-30 or 10-50 receptacle and didn't think this out when putting a GFCI on it. Presuming the GFCI is a circuit breaker type. I don't think GFCI breakers have the N-G fault detection circuitry that GFCI receptacles have, so it won't necessarily trip immediately on a N-G fault, but will if there is 4-6 mA or more flowing on the protected neutral that didn't originate from the protected ungrounded conductors.

 

[synchro]

Is EGC to oven connected to EGC/grounded conductor at panel or did it happen to get connected to GFCI load neutral terminal?

Could happen if someone happened to use a 10-30 or 10-50 receptacle and didn't think this out when putting a GFCI on it. Presuming the GFCI is a circuit breaker type. I don't think GFCI breakers have the N-G fault detection circuitry that GFCI receptacles have, so it won't necessarily trip immediately on a N-G fault, but will if there is 4-6 mA or more flowing on the protected neutral that didn't originate from the protected ungrounded conductors.

Along those same lines, perhaps a conductor from a GFCI breaker load neutral was brought to the oven receptacle and connected to the ground terminal of the receptacle. Then putting the oven on top of the cooler could've created a bond between neutral and EGC. That would create a parallel path for current flowing through the neutral bar (and busbar for plug-in breakers), and this may have diverted enough current through the neutral conductor over to the oven outlet to cause the GFCI to trip. Wiring the ground terminal of the oven receptacle to the neutral as above could also create another neutral/EGC bond through the receptacle yoke. But if so, perhaps that wasn't quite enough to trip the GFCI by itself.

 

[kwired]

Along those same lines, perhaps a conductor from a GFCI breaker load neutral was brought to the oven receptacle and connected to the ground terminal of the receptacle. Then putting the oven on top of the cooler could've created a bond between neutral and EGC. That would create a parallel path for current flowing through the neutral bar (and busbar for plug-in breakers), and this may have diverted enough current through the neutral conductor over to the oven outlet to cause the GFCI to trip. Wiring the ground terminal of the oven receptacle to the neutral as above could also create another neutral/EGC bond through the receptacle yoke. But if so, perhaps that wasn't quite enough to trip the GFCI by itself.

Is what I was thinking of when I posted before.