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Current on grounding conductor on high resistance grounded system

Current on grounding conductor on high resistance grounded system

Current on grounding conductor on high resistance grounded system

(OP)
Hello All.  I have been lurking for a while and finally decided to join.  

My issue is on a 4160/480V, 5A resistance grounded system.  I am getting an amp reading of about 66 amps on the grounding conductor attached to the cable tray coming out of the building.  The current then splits between the transformer case and the grounding grid.  The amp clamp reads 0 amps between the NGR and the X0 of the transformer.  

I thought I would have a maximum of 5A with this resistor during a ground fault.  BUT, we don't seem to have a ground fault...there is a ground fault monitor (Federal Pioneer DSP-MKII) for the MCCs and also a NGR monitor (Startco SE-325) on the main from the transformer and neither of them are alarming.

My question is where could this current be coming from?    

RE: Current on grounding conductor on high resistance grounded system

Classic ground loop.  Have fun, the extraneous ground connections can be a real bear to track down.

RE: Current on grounding conductor on high resistance grounded system

Don't confuse system grounding with equipment grounding.  These are very different.  

It doesn't take much voltage difference to push 66 amps through a grounding system.  I assume this is ac current and not dc?  The frequency spectrum of the 66A would be interesting to know.  

 

David Castor
www.cvoes.com

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