3 phase 208v GFCI modules serving commercial conveyor oven.

[Ephraim.Barlow]

Has anyone had any experience with 3 phase 208v pizza conveyor ovens randomly tripping GFCI modules? I have not been able to find any correlation with timing and have not been able to successfully consistently reproduce the issue while I am monitoring it. I have taken a Meter reading of the line and load side of the module and I have 0.99A of imbalance (measuring all three phases at the same time.) on the load side and 0.77A on the line side of the module. there is a 33% difference in the load per phase e.g. 68A (A), 33A+/- on (B) and (C) phase. (My guess is this is just sequential element rotation.) The other factors to consider are the module runs one of three identical ovens two of which do not have GFCI protection (Installed pre 2020) We definitely are able to recreate a trip by unplugging/plugging the cord in this I understand but when it just randomly trips with no apparent indicators it has me stumped. Is there a good tool for testing the insulation on the wiring and the current leakage on the case frame of the stacked ovens available in the market?

 

[gene6]

Is there a good tool for testing the insulation on the wiring and the current leakage on the case frame of the stacked ovens available in the market?

I have always used a megger for testing insulation. You need to be careful and make sure you don't leave anything in circuit, just the wires or motor leads etc.

 

[ptonsparky]

Are the GFCI tripping because of inductive kickback of contactors coils? Snubbers on those coils should help if that's the case

 

[Ephraim.Barlow]

Are the GFCI tripping because of inductive kickback of contactors coils? Snubbers on those coils should help if that's the case

That is something that could make sense. Can you Educate me a little on this a little? What are snubbers?

 

[ptonsparky]

Snubbers is probably the wrong term but I never remember what it is. SPD.
Basically when power is removed from coil the collapsing field generates a short term spike that can affect GFCIs. I used RKE but there are others.

 

[gene6]

We definitely are able to recreate a trip by unplugging/plugging the cord in this I understand but when it just randomly trips with no apparent indicators it has me stumped.

I would unhook the cord from the oven check the cord and the cord cap with a voltmeter on ohms. there should be no continuity between any of the conductors.

 

[Jraef]

Snubbers is probably the wrong term but I never remember what it is.

“Coil surge suppressors”, which would be INCLUSIVE of RC snubbers, but could also be MOVs or diodes

 

[Ephraim.Barlow]

“Coil surge suppressors”, which would be INCLUSIVE of RC snubbers, but could also be MOVs or diodes

Thank you. this definitely makes sense to me. another item that I was thinking is maybe inductance between the three circuits I am not sure how close or how the circuits are routed to the panel. The circuit we installed is in MC but I think both the existing ovens were ran in the same conduit and that for sure could give us more than 5mA of induced current on the ground conductor. Am I correct in this thought process? If so what would be the cure for bleeding this current to ground so it does not backfeed onto the new circuit?

 

[ptonsparky]

The GFCI does not care how much current is on the EG. Its looking for a current imbalance on the phase conductors. You could be sharing the EG with another piece of equipment that has a continuous 5 amp ground fault.

 

[Ephraim.Barlow]

The GFCI does not care how much current is on the EG. Its looking for a current imbalance on the phase conductors. You could be sharing the EG with another piece of equipment that has a continuous 5 amp ground fault.

Do you think this could potentially induce over 5mA current one way or another into the phase conductors in the 50' run if the other EGC are not properly connected? This Physics theory is a little above my head.

Has anyone had any experience with 3 phase 208v pizza conveyor ovens randomly tripping GFCI modules? I have not been able to find any correlation with timing and have not been able to successfully consistently reproduce the issue while I am monitoring it. I have taken a Meter reading of the line and load side of the module and I have 0.99A of imbalance (measuring all three phases at the same time.) on the load side and 0.77A on the line side of the module. there is a 33% difference in the load per phase e.g. 68A (A), 33A+/- on (B) and (C) phase. (My guess is this is just sequential element rotation.) The other factors to consider are the module runs one of three identical ovens two of which do not have GFCI protection (Installed pre 2020) We definitely are able to recreate a trip by unplugging/plugging the cord in this I understand but when it just randomly trips with no apparent indicators it has me stumped. Is there a good tool for testing the insulation on the wiring and the current leakage on the case frame of the stacked ovens available in the market?

Update:
I have found more information on this and it looks that as was suggested above the relay coils are prone to malfunction on these particular units, also the heating elements going out and tripping the high heat sensors thus calling for the coils to open ( This would be more of a one time occurrence because you have to do a manual reset of the high heat sensor trips).