Bonding Service Transformer and Grounding Electrode System

[strap89]

I've never been asked to do this before and can't find any information, but something seems funky about it.

We have a medium voltage delta:wye transformer (26.4kV:4.16kV) properly grounded per all requirements. This feeds a 4.16kV medium voltage 1500 hp motor drive where I am establishing a grounding electrode system at the first protective device. Additionally, there is a second service in the building which is 480Y/277V for all standard utilization equipment. I have permission for multiple services in this facility.

The reviewer who represents the end user (not an AHJ) has asked us to bond the transformer ground with the motor drive GES (grounding electrode system) and the building GES...something seems wrong about this, but I can't find a standard to clarify. My gut tells me that you can't bond the medium voltage drive GES with the building GES, but I'm not certain about the bond between the MV transformer and the medium voltage drive GES.

Thanks for the help.

 

[big john]

You bond everything together.

Per 250.191 all the rules for low voltage GES also apply to high voltage systems.

And 250.50 says that all described electrodes shall be bonded together.

As a general explanation, during a fault you want everything as close to the same potential as possible, regardless of whether it's on the MV or LV side. The only way to achieve that is extensive bonding.

 

[Smart $]

You bond everything together...

+1

:happyyes:

 

[cuba_pete]

Odd that he's never been asked to do this before.

Seems pretty common...as in...the only way I do things.