Grounding multiple services

[rwkaei]

I am designing the electrical system for a building addition at a high school. The new addition will be attached to the existing building, separated by fire walls.

A new electrical service with new utility transformer will be installed approximately 400' from the existing utility transformer and service.

There was a request from the owner to provide a ground from the new data/telecom room to the existing data/telecom room. I was working on my details sheet and came up with the following question....

The new service would normally include a ground wire to a ground bar in the new data/telecom room. Do I not do this and ground the new bar in the new room to the existing room per the owners request?

Which leads me to my next question...do I need to ground the two services together? There will be a new water service for the building additions well.

New grounding system will consist of ground rods. The grounding system used by the existing building is unknown.

 

[chris kennedy]

Welcome to the Forum.

A new electrical service with new utility transformer will be installed approximately 400' from the existing utility transformer and service.

This sentence does not make sense. I believe you mean the same tranny not service???

There was a request from the owner to provide a ground from the new data/telecom room to the existing data/telecom room.

If fed by the same POCO (power company) tranny you have that path via the grounded conductor.

The new service would normally include a ground wire to a ground bar in the new data/telecom room.

Yes 800.100.

Do I not do this and ground the new bar in the new room to the existing room per the owners request?

How much money do they have?

There will be a new water service for the building additions well.

New grounding system will consist of ground rods. The grounding system used by the existing building is unknown.

If the new water consists of 10' or more of underground copper and if the new footer has steel in it you will need to use both as grounding electrodes as per, 250.50.

I would like to add that the schools we do here usually have engineered specifications that go well above and beyond the minimum requirements of the NEC.

 

[augie47]

I can see reason for concern but would rely on shaper posters for an answer.'
From what I read you have a "technically" separate building (due to fire walls) and separate service fed by separate transformer.
It would seem there might be potential for some unwanted current flow thru computer circuits that were common to both buildings.
My first thought would be to bond the grounding electrode system for each building together to establish a 0 potential but I can't honestly say that would be necessary or sufficient.
In essence, I can only support your (their) concern.

 

[rwkaei]

Yes, by "separate service" I mean separate service entrance section, SES, main distribution board, whatever you like to call it. The existing utility transformer and it's SES will remain for the existing building.

 

[pete m.]

My first thought would be to bond the grounding electrode system for each building together to establish a 0 potential but I can't honestly say that would be necessary or sufficient.

I can't find an NEC requirement to bond the GES for each service from each building together. I agree with Gus that it is probably a good idea but I can't find a mandatory requirement.

Pete