Bonding service

[Dave58er]

500kva transformer outside, near the electrical room, with 4 ground rods at the corners of the pad connected and brought up into the transformer. Transformer is 13.2/480.

We install 2 ground rods for grounding electrodes for the service inside. Do you connect the 2 sets of ground rods or leave them isolated? They are within ten feet of each other.
I've been told the old way (10 years ago) was to never connect them, but that now everyone connects them.

The services I've worked on in the past were completly engineered and built to the spec. sheets, usually on industrial jobs with very elaborate ground mats. I don't think I paid as much attention to some of these details as I should have.

 

[iwire]

Do you connect the 2 sets of ground rods or leave them isolated?

They are connected already by the grounded conductor from the transformer to the switchgear. The grounded conductor is likely to be much larger than any conductor of the GES so it is a more effective fault path as well.

An additional conductor would essentially create an additional path for unbalanced neutral current, and while that may not be harmful it will never be helpful.

Think of a typical residential service.

Would you ever consider running an additional jumper from the homes grounding electrodes to the power companies electrodes?

 

[Dave58er]

They are connected already by the grounded conductor from the transformer to the switchgear. The grounded conductor is likely to be much larger than any conductor of the GES so it is a more effective fault path as well.

I agree with that Bob. I had some of the same thoughts but couldn't get them organized in my head that way.

An additional conductor would essentially create an additional path for unbalanced neutral current, and while that may not be harmful it will never be helpful.

I should have thought of that. Thats precisely the reason the service to the building is 3phase 4 wire, if we connected them it would be like changing to 5 wire.

Think of a typical residential service.

Would you ever consider running an additional jumper from the homes grounding electrodes to the power companies electrodes?

Again I agree and again you make it seem obvious now.
Pretty good since you had to think about it for at least 30 sec.

 

[iwire]

Pretty good since you had to think about it for at least 30 sec.

Well thanks, but to be honest it is a question that has come up before.