Grounding on Genetators

[Frank Bologna]

We are trying to make safe electrical installations on grounding issues.....some body has put ground rods at the generator and all the sub-panels following. I am thinking that multiple ground rods at various locations create a danger in itself as the difference of potential between ground rods may induce a current on the grounding path.

To clarify the installation:
We have 2 120kw generators connected to a main transfer switch which also breaks the neutral, to a main distribution panel which feeds various sub-panels located thru-out the compound.
Should we disconnect all the ground rods at the subpanels and make all the fault current return to the source via the equipment grounding conductor?
Thanks for the help!

 

[don_resqcapt19]

As long as the ground rods are only connected to the EGC and not to the grounded conductor, there is no issue with ground rods at all of those locations.

 

[ceb58]

We are trying to make safe electrical installations on grounding issues.....some body has put ground rods at the generator and all the sub-panels following. I am thinking that multiple ground rods at various locations create a danger in itself as the difference of potential between ground rods may induce a current on the grounding path.

To clarify the installation:
We have 2 120kw generators connected to a main transfer switch which also breaks the neutral, to a main distribution panel which feeds various sub-panels located thru-out the compound.
Should we disconnect all the ground rods at the subpanels and make all the fault current return to the source via the equipment grounding conductor?
Thanks for the help!

As long as the ground rods are only connected to the EGC and not to the grounded conductor, there is no issue with ground rods at all of those locations.

I will say that 250.30 (A) (4) will come in on the generators. Since you are switching the neutral they are a separately derived system. The grounded conductor must be bonded to the GEC. Multiple SDS can share a common grounding electrode. After that,as Don said, the rods are ok at the subs as long as they are not connected to the grounded conductor.

 

[quinn77]

if this compound consists of multiple bldngs and structures...250.32(a) would require the electrodes.

 

[tryinghard]

We are trying to make safe electrical installations on grounding issues.....some body has put ground rods at the generator and all the sub-panels following. I am thinking that multiple ground rods at various locations create a danger in itself as the difference of potential between ground rods may induce a current on the grounding path.

To clarify the installation:
We have 2 120kw generators connected to a main transfer switch which also breaks the neutral, to a main distribution panel which feeds various sub-panels located thru-out the compound.
Should we disconnect all the ground rods at the subpanels and make all the fault current return to the source via the equipment grounding conductor?
Thanks for the help!

The ground rods are there for "lighting, line surges, or unintentional contact with higher-voltage lines" (250.4(A)(1)) they are not there for fault current, downstream anyway. "The earth shall not be considered as an effective ground-fault path." 250.4(A)(5). What's most critical is not creating a parallel neutral path by bonding the grounded conductor twice and also to re-establish the earth connection if the transfer switch operates the grounded conductor.