Seperatly derived system bonding confusion

[riverjig87]

We are installing the electrical system in a hospital. Each floor has its own electrical services. They are fed from the main gear downstairs. On each floor, we have 120\208 and 277\480 services. The question is since every floor has med gas pipes, med vacuum pipes, and cold water, do we need to run a seperate bond from the xo of each of these transformers to these pipes passing thru each floor? Does this suffice for the bonding requirements of the seperatly derived systems? ( My logic is that these systems are adding a difference in potential so they must be bonded in order to make the zero potential needed for a grounding system) Also, each floor has a grounding plate that serves as the grounding electrode, located directly underneath each electrical room.

I am not certain that I overthought this to death and would like clarification.
Thanx for any input.

 

[LarryFine]

Seems to me that bonding the X0 to the grounding plate is ideal, as long as there are appropriate bonds between said plate and the various piping systems.

I would not say that the piping on each floor need be redundantly bonded; that should have been done at the main service, and continued via these plates.

 

[riverjig87]

Still questionable

Still questionable

I agree. These med gas pipes and cold water supply run up thru each floor and supply each floor, originating at a common mechanical equipment room. The confusion lies with each seperate service on each floor requiring this bond in order to create a fault path from these seperatly derived services. It seems to me that if the med gas pipes are bonded in the main equipment room on the first floor where they originate, that would meet the requirement.

 

[zyhml]

i am not certain if different volt rating system could connect to the one grounding electrode. According to 250.60, lps electrode shall be seperated from power grounding electrode(not prohibit bonding).

 

[don_resqcapt19]

Also, each floor has a grounding plate that serves as the grounding electrode, located directly underneath each electrical room.

How does a plate on an upper floor become a grounding electrode?

The code spicifically requires a local bond to a metal water piping system and to exposed structural metal. See 250.104(D). The code does not require the SDS to be bonded to other metal piping systems, but I think it would be a good idea.

Don