Service w/ approx 70 GFCI's tripping; need help thinking through.

[ptonsparky]

I wonder if in order to save money, they are using the same circuit board in the breakers as the arc faults? Just changing the software (or maybe not) No need to change the assembly line when switching back and forth during production? We all know the issues arc faults have.

In particular, some QOs.

Guessing all those GFCIs were the same mfg date.

 

[brantmacga]

Met with utility engineer this morning, and have since spoken to two more over the phone.

A couple of utility issues; the lineman who connected service spliced 350 to 3/0 for xfrmr taps. Engineer said he saw significant overheating issues with IR on those conductors. Also, this was a tear down/rebuild on the same site, and they maintained the existing transformers which are undersized according to the last engineer I spoke to. They scheduled an outage for next week to correct the issues. Hopefully this will resolve my issues.


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[brantmacga]

The utility ended up coming overnight on the 26th. The store manager reported that one GFCI tripped the day after on the 27th, but none since then. Fingers crossed this has actually worked.


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[brantmacga]

approx five GFCI breaker trips now since I last posted.

 

[hillbilly1]

Th

approx five GFCI breaker trips now since I last posted.

Those probably could be attributed to wash downs of equipment.

 

[synchro]

Th

Those probably could be attributed to wash downs of equipment.

Good point. And those wash downs could be longer and more intensive because of the COVID-19 situation, making tripping more likely. You'd need to check which equipment is supplied by these breakers to determine if this is a possible explanation.

 

[brantmacga]

Th

Those probably could be attributed to wash downs of equipment.

This equipment isn’t washed down.

One was a fryer control circuit, one was a heated cabinet, two are ovens, the other is a headset controller.


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[ramsy]

Can RTU's, or other suspects, get LOTO for a few days?

 

[hillbilly1]

This equipment isn’t washed down.

One was a fryer control circuit, one was a heated cabinet, two are ovens, the other is a headset controller.


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The heated cabinet, and ovens I can see, the fryer control circuit and headset controller, (well maybe the headset controller if it has a surge protector plugged in) would be a mystery.

 

[Todd0x1]

Does the fryer have a pinched wire somewhere? Could the ignitor circuit leak enough current to ground to trip gfi (I don't know how those work, just thinking out loud)?

 

[brantmacga]

Can RTU's, or other suspects, get LOTO for a few days?

0% chance


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[maxbillington]

GFCIs are built with a CT around the Hot and Neutral; poly-phase GFCIs have their CTs around the phase legs. As long as the current flowing into and out of the CT are equal, the magnetic fields are equal and opposite, and they cancel each other out. The CT sees zero current. They are set to trip if there is a current imbalance of about 5 milliamps.

If you are having intermittent tripping of several GFCI devices you probably have one piece of kitchen equipment that is connected line to ground rather than line to neutral. This piece of equipment is not used every day, but when it is used, the line to ground current returns home to the XO lug of the supply transformer through all the pathways available. That means there is line to ground current on all the ground wires, but also these currents will flow through the neutrals. If the line to ground currents exceed 5 milliamps at any of the many GFCIs you will get a GFCI trip.

If you have installed the branch circuit distribution system with proper isolation between ground and neutral, then there is a piece of equipment, or pieces of equipment, that are connected line to ground. New residential appliances often are delivered with a neutral-ground link. That link must be removed when the appliance is terminated. Look for new appliances and check their neutral connection and make sure they are isolated from the equipment ground.

If your installation is part of a multi-tenant space, all fed by the same service transformer, there could be a line to ground connection in an adjacent tenant space that is the culprit.

You are spending a lot of effort trouble shooting this. I recommend you place a recording meter at the main service and monitor all phases, neutral and ground. Be watching for ground current that is intermittent. Then if you discover a time of day when the current occurs, have the owner find out what equipment was opprating at that time.

 

[texie]

If your installation is part of a multi-tenant space, all fed by the same service transformer, there could be a line to ground connection in an adjacent tenant space that is the culprit.

Sorry, but this is not correct. A neutral to ground connection upstream of a GFCI device will have no effect on the proper operation of the GFCI.

 

[brantmacga]

If you are having intermittent tripping of several GFCI devices you probably have one piece of kitchen equipment that is connected line to ground rather than line to neutral. This piece of equipment is not used every day, but when it is used, the line to ground current returns home to the XO lug of the supply transformer through all the pathways available.

............

You are spending a lot of effort trouble shooting this. I recommend you place a recording meter at the main service and monitor all phases, neutral and ground. Be watching for ground current that is intermittent. Then if you discover a time of day when the current occurs, have the owner find out what equipment was opprating at that time.

I’m not sure a N-G fault on one circuit could affect the GFCI on another; it technically should not. I’m still trying to wrap my head around the possibility of how this could function. That would mean a fault would travel through the bonding point, down the grounding path of another circuit, then return through the neutral wire of that circuit. Right?

They are experiencing GFCI trips almost daily, and at all hours of the day. I can’t think of any equipment that isn’t used every day.


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[texie]

I’m not sure a N-G fault on one circuit could affect the GFCI on another; it technically should not. I’m still trying to wrap my head around the possibility of how this could function. That would mean a fault would travel through the bonding point, down the grounding path of another circuit, then return through the neutral wire of that circuit. Right?

They are experiencing GFCI trips almost daily, and at all hours of the day. I can’t think of any equipment that isn’t used every day.


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I know I ask before about mixed neutrals and/or grounded neutrals downstream of the GFCI but have you actually verified this with an ohmeter? This is pretty straight forward to do.

 

[brantmacga]

I know I ask before about mixed neutrals and/or grounded neutrals downstream of the GFCI but have you actually verified this with an ohmeter? This is pretty straight forward to do.

It would trip every single time if they were mixed (under load). I have done a rough verification by verifying color coordination; We use striped neutral wires. I was on-site when the service was first energized, and there were three circuits out of the 250 or so total that had the neutrals crossed up. I also had the job foreman back down there a couple of weeks ago overnight going through circuits again to verify neutrals.


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[kwired]

Sorry, but this is not correct. A neutral to ground connection upstream of a GFCI device will have no effect on the proper operation of the GFCI.

I agree. Line side causes needs to be because of things like surges, RF interference, maybe harmonics and could even be causing problems with the GFCI control circuitry more so than introducing current into the CT of the GFCI.

 

[hillbilly1]

It would trip every single time if they were mixed (under load). I have done a rough verification by verifying color coordination; We use striped neutral wires. I was on-site when the service was first energized, and there were three circuits out of the 250 or so total that had the neutrals crossed up. I also had the job foreman back down there a couple of weeks ago overnight going through circuits again to verify neutrals.


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Yeah, with a mixed up neutral, the breaker would never hold when load was applied. I’m betting they are using the same chip they use in the arc fault breakers, with it, follows the same issues.

 

[brantmacga]

Between 6pm yesterday and noon today, five GFCI’s tripped, and two will not reset.

Square D account manager thinks they’ve tripped so many times they are now unreliable, and wants to ship replacements for every GFCI in the service.

I’m apprehensive about dropping $10k in replacement breakers without knowing the problem is solved. They think the utility work likely fixed it.

I’ve asked for 2nd opinions from engineering.

The equipment on the breakers that won’t reset has been plugged in elsewhere and is working .


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[retirede]

The equipment on the breakers that won’t reset has been plugged in elsewhere and is working .


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Then the problem has to be with something on the original circuit - wiring or breaker.