current on grounding conductor

[mikejs]

I have a 3 phase 480/277v 4000a service with a 1200a refrigeration sub-panel that is monitored by the refrigeration company and they are getting a current reading on the grounding conductor, it was as high as 30a but I did some checking and we found the generator had a bounding jumper and our transfer switch was a 3 pole. Once we removed the jumper we were getting around 12a. Our voltage to neutral varies from L1-N 270v, L2-N 277v, L3-N 283v, L1-L2 475v, L2-L3 483v, L3-L1 481v. This is in a 400,000 sqft newly constructed freezer/dry warehouse. I would appreciate any feed-back

 

[texie]

I have a 3 phase 480/277v 4000a service with a 1200a refrigeration sub-panel that is monitored by the refrigeration company and they are getting a current reading on the grounding conductor, it was as high as 30a but I did some checking and we found the generator had a bounding jumper and our transfer switch was a 3 pole. Once we removed the jumper we were getting around 12a. Our voltage to neutral varies from L1-N 270v, L2-N 277v, L3-N 283v, L1-L2 475v, L2-L3 483v, L3-L1 481v. This is in a 400,000 sqft newly constructed freezer/dry warehouse. I would appreciate any feed-back

Sounds like you are on the right track in determining the source of the current on the EGC. Maybe there are other inadvertent neutral to ground bonds in the system. But I have to wonder, once you get readings on the EGC down this low on a 1200 amp circuit how much of that might be just induced current on the EGC. Maybe others more schooled than I can comment.
Also there could be a compressor leaking some current to ground which would indicate a possible future failure. You don't mention if there are 1 or many units on this panel, but maybe you could measure the EGC current while isolating them individually.

 

[mgookin]

... they are getting a current reading on the grounding conductor, ...

Does this happen only when the generator is running?
Or when it's not running?
Or both?

 

[weressl]

I have a 3 phase 480/277v 4000a service with a 1200a refrigeration sub-panel that is monitored by the refrigeration company and they are getting a current reading on the grounding conductor, it was as high as 30a but I did some checking and we found the generator had a bounding jumper and our transfer switch was a 3 pole. Once we removed the jumper we were getting around 12a. Our voltage to neutral varies from L1-N 270v, L2-N 277v, L3-N 283v, L1-L2 475v, L2-L3 483v, L3-L1 481v. This is in a 400,000 sqft newly constructed freezer/dry warehouse. I would appreciate any feed-back

If it is a large and excessive system and continuously moisture laden, you maybe seeing capacitive coupling current beween the conductor and earth/ground and the insulation acts as dielectric.

 

[mikejs]

Does this happen only when the generator is running?
Or when it's not running?
Or both?

when it's not running

 

[Sahib]

mikejs:

If the ground current of 12A you mention is on the ground conductor to sub refrigeration panel, the problem is solved:because there should be no neutral to ground bond. So the ground current for this panel should be due to any incipient phase to ground fault or neutral to ground fault or both.
So check this panel and rectify the fault.

 

[George Stolz]

Sahib, the main bonding jumper could produce the same results. You could guess any point in the system with equal odds of guessing right.

The only solution is tracking it down systematically.

 

[Sahib]

stolz:
The main bonding jumper is in the service entrance panel. So if the grounding wire to sub refrigeration panel is tapped from a separate ground bus bar away from the sub panel and the mentioned 12A is measured in that ground wire, then the cause of the 12A ground current may be the ground fault in the sub panel. This may be confirmed by disconnecting the ground wire and checking if there is any appreciable voltage between the sub panel and remote ground after taking necessary precautions.
One surprising thing is that a ground leakage current of 0.2mA and above on any appliance may produce a shock. But here no shock effect was reported by the OP.

 

[GoldDigger]

Sahib:
Ground leakage current of any value that is being carried by a properly EGC will not be a shock hazard. But it does emphasize that interrupting the EGC will not be a good troubleshooting tool.

Tapatalk!

 

[Sahib]

GoldDigger:
So no problem due to the ground leakage current of 30A or 12A in the OP's case for the time being.

 

[GoldDigger]

Well, it could well be s sign of very severe and potentially dangerous leakage, but not with an expectation of reported shocks.
Or it could simply be the result of an extra ground-neutral bond which could not produce a hazardous or palpable voltage.

Tapatalk!

 

[Sahib]

GoldDigger:
So wherever bonding is visible, no shock hazard exists there. But where moisture is present or in damp or wet environment is encountered in the OP's situation, for example, checking is required to detect any presence of touch or step potentials and in case of their presence, fault rectification is required.

 

[GoldDigger]

Any resolution of the problem must start with identifying the source of the current. Only then can it be determined what additional steps are required.

Tapatalk!

 

[Sahib]

My guess is the sub refrigeration panel is the culprit.
Yours?

 

[Sahib]

Any resolution of the problem must start with identifying the source of the current. Only then can it be determined what additional steps are required.

Tapatalk!

If the identification of source is difficult, the precautionary measure
mentioned in

where moisture is present or in damp or wet environment is encountered in the OP's situation, for example, checking is required to detect any presence of touch or step potentials

should be initiated immediately.

 

[George Stolz]

My guess is the sub refrigeration panel is the culprit.
Yours?

Thank you for clarifying that you are just guessing. I maintain that systematically tracking down the ground fault is necessary.

This may be confirmed by disconnecting the ground wire and checking if there is any appreciable voltage between the sub panel and remote ground after taking necessary precautions.

Necessary precautions to opening the EGC would include shutting the power off, which would be the much easier, conclusive and far less dangerous method of tracking the ground fault down systematically. Opening the EGC while still both energized and uncertain of the source of the fault would be extremely dangerous and foolhardy, as you run the likelihood of energizing exposed metal parts to a higher shock potential.

 

[Sahib]

Necessary precautions to opening the EGC would include shutting the power off, which would be the much easier, conclusive and far less dangerous method of tracking the ground fault down systematically. .

What a beautiful,simple effective alternative.:thumbsup:

 

[don_resqcapt19]

...
One surprising thing is that a ground leakage current of 0.2mA and above on any appliance may produce a shock. ...

That is interesting...the UL standards for residential appliances permit leakage current of up to 0.5mA.

 

[Sahib]

That is interesting...the UL standards for residential appliances permit leakage current of up to 0.5mA.

Perhaps the standards mean this 0.2mA or 0.5mA ground leakage current spreading around the surrounding ground from the subject appliance under earth fault other than its ground leakage current entirely through the EGC connected to it and distributed by other connected metals including the building steel, liable to give a shock.

 

[kwired]

My guess is the sub refrigeration panel is the culprit.
Yours?

Could easily be someone made a mistake and crossed a neutral with an equipment grounding conductor at some piece of equipment, or damaged insulation on a neutral conductor is contacting a grounded object in some remote location, could be pinched by a box cover or something really simple like that, but could take hours or even days to find it.