NESC vs NEC Grounding

[cripple]

I have an electrical design which shows a pad with a utility transformer and a customer owned distribution switchboard. The grounding detail shows the utility transformer and the switchboard neutral (grounded) conductor being grounded to same concrete encased electrode in the pad. I told the design engineer that I did not think this met Code, because the grounding electrode system would be paralleled with the neutral between the utility transformer and the switchboard. His response was, the utility transformer is required by the NESC to be grounded, and NEC requirements did not apply. This is my first installation with the utility transformer and the customer owned equipment being placed on the same pad. Any comments?

 

[LarryFine]

My first impression: unless you can use the EGC between the transformer and your switchboard as the bond for your neutral, you're right, sounds like there's a conflict, and I suggest approaching your AHJ.

He may say that you're required to do what you're required to do, we have no control over what the POCO does, and like the neutral and EGC between a meter and a main, it'll just have to be done that way.

 

[jtester]

My first impression: unless you can use the EGC between the transformer and your switchboard as the bond for your neutral, you're right, sounds like there's a conflict, and I suggest approaching your AHJ.

He may say that you're required to do what you're required to do, we have no control over what the POCO does, and like the neutral and EGC between a meter and a main, it'll just have to be done that way.

In most utility installations there is no separate EGC between the utility xfmr and the switchboard. There should be a solid bond between the grounding at the switchboard, if it is the service disconnect, and the utility neutral.

If I read the original description correctly, there is no problem.

Jim T

 

[LarryFine]

I was envisioning metallic conduit, but you're right if I'm wrong.

I believe the original post meant that the neutral at XO is grounded within the transformer, would be grounded again in the switchboard, and since they're sharing a grounding electrode, would place the GEC's (XO to rod and switchboard neutral to rod) and the service neutral in parallel.

I was suggesting omitting one of the GEC's; the panel's one, but that's a no-no, too.

 

[jtester]

I believe the original post meant that the neutral at XO is grounded within the transformer, would be grounded again in the switchboard, and since they're sharing a grounding electrode, would place the GEC's (XO to rod and switchboard neutral to rod) and the service neutral in parallel.

The neutral,X0, should be grounded at the transformer, and the service neutral should be grounded ath the switchboard as well. This will place neutral and earth in parallel across the service entrance conductors, but that is common on nearly every grounded service anyway.

Jim T