Objectional Current on Equipment grounding conductor

[golf99]

I have two gensets feeding a manual 3-pole xfer switch. It feeds an MDP which then feeds 8 SDPs. All 5 wire. 3-phase 4-wire and 1 Equipment grounding conductor. Genset 1 is bonded ,the other is not per the NEC. I have checked for an internal bond at genset 2 but dont get a continuity reading from neutral to ground. I have 8 amps on the EGC from MDP to SDP back to the gen set that is running. Nothing on the idle one. When i disconnect the 8 EGCs from the SDPs at the MDP I still have 3 amps back to the gen set. Why ? As I add the EGCs back on one at a time the current increases back to the 8 amps. The second issue I am now trying to identify is the source of the current coming from the trailers. I eliminated some misplaced bonding jumpers that created parallel paths. Also, the panels in the trailers are RCD protected rated at 30ma.. They are not tripping.. Induction from the phase conductors to ground wires ? Any help would be appreciated ! Thank you.

 

[waross]

I would start by disconnecting the groud connection on the generator.
I am assuming that you have added a transfer switch and generators to a code compliant installation. (In North America)
The main neutral to ground connection in the main panel is the one point ground connection. With three pole transfer switches, the main ground connection that serves when you are on utility power willstill serve when you are on generator power. I fear that you may have added a second neutral to ground connection at the generator and created either a ground loop or, more likely, neutral current sharing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[golf99]

I have 2 gensets and no utility power.The bondinging jumper (N-G) is at genset 1.. 250.20(d)fpn 1.
Genset 2 is not bonded.. An equipment grounding conductor is installed from both gensets to xfer switch to MDP to SDPs.
A better (safer) design that you mention would be to install main bonding jumper at the MDP with no MBJ at the gensets. that way if genset 2 is replaced or removed for maintenance the neutral is not connected. The 3-pole transfer switch does not allow for each genset to be a separately derived system.. A 4-pole would.I think the system is installed correctly as per the NEC..There are no other bonding jumpers that are creating parallel paths that I can see or measure.. I have worked on other identical systems and have not had this same problem.. I have been researching current on the equipment grounding conductors and have found a few good articles..
Some current on the equipment grounding conductor during normal operation is usually found. Induced currents from adjacent phase conductors, induced currents from motors, capacitive coupling between the phase and neutral to the grounding conductors in long circuits etc.. Is it possible in this configuration that some current is flowing thru the neutral connection at the xfer switch and then thru the 2nd gen windings to ground ? I have removed all grounds one at a time and cant seem to pinpoint the source. I simulated a 4-pole switch and still had current on the egc at the running gen.. I also checked for an internal bond at the gen. I think that would create a parallel path from MBJ connection in the breaker enclosure to the J-box that sits inside near the engine.. Thanks for your interest and help. I appreciate it ..

 

[golf99]

Please check out the attachment. This is the diagram that shows how the system is connected.
Thanks again