Amperage on Ground Wiring

[ken44]

I have two 1200 amp ATS's at one of our facilities in which we just had a new 1.6 megawatt generator installed to back up the data center, during testing the generator was shutting down due to a ground fault so we did some additional testing over the weekend and during this testing, the generator contractor adjusted the ground fault setting from 10 amps to 100 amps and while the load was maintained, we still have a ground fault indicator light that is "on". Now that I have established some background, my question is concerning, the generator company used the electrical contractor that subbed for them on the generator installation to come out and take some readings and here is what they wrote back to us-

"We had Robert G. go out to TFS building and take some ground readings. There was 12 grounding wires at the panel .This is what he found at the Main Switch Gear. Looking at the Main Switch gear form Left to Right 7.6, 15.9 ,0 ,11 ,12.8, 4.7 this is the first six wires. Now the second six wires 7.9, 17.8, 12.8, 2.9, 3, 3 these readings are in amps. We did not see a bond wire between the ground and the neutral. Robert told me that one of the maintenance men was looking at the meter with him. You should not have any amps on the ground wire."

I know that there should not be any amperage on the ground wire and that the neutral and ground should be bonded at the Main Service but they only indicate that they did not see one so it does not mean that it may not be present-this faciltiy has been around for years and we have not had any issues previously indicating that this could be a problem. I have seen amperage on ground wires before and I am trying to get some ideas as to how others may have handled similar situations.

 

[don_resqcapt19]

The most common cause would be more than one neutral to ground connection. Was one added when the generator was installed?

 

[brian john]

Are the ATS's 33 pole or 4 pole?

Check the grounding at the generator and verify the you have grounded/not grounded the neutral based on type of ATS you employed.

I assume you have this current while on generator and while on utility?

Are there UPS systems on the distribution system, If you do and they have a 4-wire bypass check grounding.

Perform a visual inspection of all distribution panels for wiring errors, some electrician still insist on grounding the neutrals downstream from the main neutral ground bond.

If all else fails during a schedule outage arrange to isolate all neutrals and megger them to check for shorts to ground. Utilize the typical divide and concur method.