I am thinking if the sub refrigeration panel is causing the ground leakage current. One easy way to check is as stolz suggested. But what if the shut down of refrigeration plants cause other problems and not allowed? In that case I think measuring the voltage drops at various points on the sub panel grounded surface, and few upstream and downstream ground points with respect to remote ground i.e at the main bonding jumper and without disconnecting the EGC will provide the necessary clue.
current on grounding conductor
- Thread starter mikejs
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I am thinking if the sub refrigeration panel is causing the ground leakage current. One easy way to check is as stolz suggested. But what if the shut down of refrigeration plants cause other problems and not allowed? In that case I think measuring the voltage drops at various points on the sub panel grounded surface, and few upstream and downstream ground points with respect to remote ground i.e at the main bonding jumper and without disconnecting the EGC will provide the necessary clue.
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Perhaps simpler would be tracking the current back with a clamp-on ammeter.
Tapatalk!
Tapatalk!
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- Windsor, CO NEC: 2017
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- Service Manager
That's a people problem, not a mechanical one. Refrigeration can be shut down in short enough intervals to isolate a potentially deadly ground fault.
Highly improbable and likely inconclusive. The quickest way to isolate it is to track it down with an ammeter, shutting off equipment in a systematic fashion to isolate the fault. Why is this a problem for you?
No problem for me but perhaps for the OP (Let him concur to your proposed 'short enough shut downs').
I am just trying to see whether it is possible to locate the fault without any shutdown.
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- Windsor, CO NEC: 2017
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- Service Manager
I misunderstood. It looked like you were declaring solutions as opposed to asking if they would work.
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- Illinois
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- retired electrician
The are appliances with EGCs and the leakage is tested between the circuit conductors and the EGC.
So what is your point, Don? Any shock felt above 0.5mA even under that condition ?
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mikejs
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- gettsburg PA
thanks for the input I had the compressors shut down and it only reduced the amps to 8a so I'm going to try each branch circuit one at a time
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- Illinois
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- retired electrician
My only point is that the standards permit that amount of leakage current. Assuming that the EGC is intact and connected to the electrical system as it should be, there is no shock hazard at that current level and when you unplug the appliance there is no longer any leakage current.
UL has used the 0.5mA in other applications, most notable is where their standards permitted things like occupancy sensors to use the EGC as the grounded conductor as long as there is no more than 0.5mA of current. That standard led to the NEC rule in 404.2(C) that requires the lighting circuit grounded conductor to be run to the light switch location.
It appears that UL believes that 0.5mA does not present a hazard.
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- Windsor, CO NEC: 2017
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- Service Manager
No, and that was likely his point.
Mike, I should add that once you believe to have the problem isolated, shutting the power off, lifting the neutral and ohming between the load side neutrals and the EGC will confirm it. I would start by lifting the panel neutral and then the branch neutrals one at a time until the problem is isolated.
Even if the ground leakage current is 0.5mA, it is likely to give a shock if the EGC is not there.
The OP stated there was reduction of leakage current in steps: 30A-12A-8A. Perhaps, the ground fault is not at one place but rather distributed. For example when he shut down the compressors, the leakage current reduction from 12A to 8A. So there might be current leakage from compressor motors to be checked individually.
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- Windsor, CO NEC: 2017
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- Service Manager
1. I'm not sure how he'd be reading 12A on an EGC that wasn't even there.
2. I suppose OSHA has their facts wrong as well, you should email them to correct this.
There may be any number of things leaking current to ground, and the presence of the extra bonding jumper indicates there may be more onsite.
1)Absence of EGC in the Don's case of leakage current on appliances as well as in the OP's case may likely cause a shock for a leakage current of 0.5mA.
2)The 0.5mA leakage current from equipment into the surrounding and not into the prospective victim. So the resulting voltage drop is the cause of the shock.
Checking those things(compressor motor for example) leaking current to ground should also be part of your 'systematic search'.
mikejs
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- Location
- gettsburg PA
I revisited the site to do some more research. 1st the readings where coming from a Rittal PQube in a box ct type monitor which is why I could not get the same readings with my fluke clamp-on. We shut down all the 480/277v circuits and only a slight chance witch I believe was from some VFD's. The only thing left was the 2-30 kva transformers witch 1 was for the IT room and the other was for the control panel and 120v support circuits for the refrigeration system. We discovered the ct monitor also had a reading for harmonic amps witch matched the amp readings on the grounding wire so is there a correction for harmonics?
If your transformer is STAR connected on the primary, harmonics current , predominantly third, will appear on the neutral and via it to the ground wire. But if the transformer primary is DELTA connected, no harmonics issue in the ground wire from the transformer.
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