Outdoor Service Transformer Grounding

[Jim Malady]

Per section 250.24(A)(2), when a service supplied tranformer is outdoors, "at least one additional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the transformer or elsewhere outside". Is it correct to say that this additional outdoor grounding connection to the grounded conductor at the trasformer should be made a grounding electrode that is NOT BONDED to the grounding electrode to which is bonded to the grounded conductor at the service disconnect?

If the same grounding electrode is bonded in both places, then a parallel path to the grounded conductor would be supplied from the neutral bus at the service disconnect to the transformer neutral. This would be undesireable?

To meet the criteria of 250.24(A)(2), is a single ground rod usually driven at the service tranformer and connected to the the transformer neutral?

 

[RUWired]

If the same grounding electrode is bonded in both places, then a parallel path to the grounded conductor would be supplied from the neutral bus at the service disconnect to the transformer neutral. This would be undesireable?

Jim, IMO this would be the same as the GEC connected to the water mains located in the cities.

To meet the criteria of 250.24(A)(2), is a single ground rod usually driven at the service tranformer and connected to the the transformer neutral?

Yes, typically a seperate rod is driven at the transformer and another for the building, but when ground rings are required and the transformer is located near the building the same ring/rod is used for equal potential reasons.

Rick