grounding seperate bldgs seperate systems

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JeffD

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I'm working on a project where 1 owner owns 2 office buildings. They share a demising wall but are 2 completely seperate buildings. The owner leased a space to a tenant. This tenant wanted more windows so the owner has this office in both buildings. the tenant then says that they want a common ground in the space because of their computer network. Everyone is just thinking run a ground from the 120/208 panel in one building to the 120/240 panel in the other building. The best I can come up with, assuming it is even allowed, is that a 3/0 should be run from the where the ground comes into one building to the other. Such as bonding the two incoming water lines together. Anyone have any views on this.

In case it matters it is on the 4th floor of an 8 story building.
 
What would be the purpose of this Grounding conductor ?
Your EGC must be installed with your power conductors from the panel that serves the receptacles.
 
The company renting the space says they want the grounding conductor bonded because they are afraid the ground will be at different potentials causing problems. they are a computer outfit. My only guess is that the Cat5/6 cable might pick it up somehow????? Otherwise the systems in each building are going to be completely isolated from one another.
 
I don't understand what exactly you think this is going to do for you. Are the receptacles being used grounded now? Is there two separate services or one service with two meters?
 
This isn't my idea. :(

This is two seperate buildings, two seperate services, two seperate distribution types, 120/240 single phase, 120/208 three phase.

the owner is requesting it because the client is requesting it.

My main questions are is it allowed and if so how?
 
Have you considered the likelyhood that your ground connecting both buildings will have neutral current current on it due to the fact that the neutral impedance of the two service neutrals is bound to differ?

This will cause neutral current bonded to the ground bus in one service entrance to travel up to your floor, across the ground you want to install, and then down to your service entrance and out that neutral.

This net current may cause problems with various electronic equipment that sits near the various pathways of the net current.

I have seen this in buildings which shared a metallic water system. The imbalanced neutral uses the water pipe to go from one service entrance to the other. But this was on the ground floor. You may be creating problems and liability with other floors and their tennants. Beware!

Karl
 
Seeing how this on the 4th floor, the service should have a disconnecting means on the ground level and the neutral and ground conductor should be seperated.Bonding the two panels together at the tenant space should not be a problem.This method of bonding is mandatory in certain sections of hospitals using only a #10awg wire.
Rick
 
Rick, reading your post again I think you were referring to the subpanels on the 4th floor. Right.

But neutral current from the neutral/ground bond at one service entrance will flow up the grounding conductor to the subpanel, then over to the other subpanel by the connecting ground wire, then down to the second service bonding point, transfering to the neutral and back to the transformer. This will happen in one direction or the other depending on the impedances of the service neutrals of the two services.

Right?

Karl
 
Guys,

thanks for the input. We told the owner today we're not going to bond the systems together in any way. If he gets someone else to do it that is going to be his problem not ours.
 
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