250-104, d-1

[Red Wiggler]

I have a situation where there are 2 water systems entering two buildings served by only one electrical service. The two buildings are connected together via an enclosed walkway, but they are not connected together by building steel.

I am required to bond to the nearest water system, and to building steel at the service, but can I provide a bonding jumper to tie the two building steel systems together, and bond the other water system to the steel in the other building?

Also, can every transformer's grounded conductor be bonded to either the nearest water line or to building steel as long as the bonding jumper is sized correctly?

 

[Smart $]

The way I see it, there's a question here whether you have one or two buildings. Only the local authorities can make that call for certain. The answer to your first question changes accordingly.

If two buildings, each building is required to have its own grounding electrode system (GES). If one building, there'd only be one GES and that would include both water systems.

Regarding structural steel, each building or section is reqiured to be bonded, but that requirement would be covered if the steel qualifies as a grounding electrode, i.e would be bonded via a grounding electrode conductor GEC.

If two buildings, bonding of the GES's is accomplished through an equipment grounding conductor run with any feeder. If one building, there would have to be a GEC between sections, and that would cover the bonding.

Regarding your second question, not only can they, each is required to have a GES established by bonding to the closest of the two types: the water supply electrode (closest of the two) or (bonded) building steel closer than the neasest water supply electrode... provided the transformer's secondary constitutes a separately derived system.

 

[Dennis Alwon]

Smart< I thought the building steel if structural needs bonding regardless if it is a electrode. 250.104(C)

 

[Smart $]

Smart< I thought the building steel if structural needs bonding regardless if it is a electrode. 250.104(C)

Not redundantly...

(C) Structural Metal. Exposed structural metal that is interconnected
to form a metal building frame and is not
intentionally grounded and is likely to become energized
shall be bonded to the service equipment enclosure, the
grounded conductor at the service, the grounding electrode
conductor where of sufficient size, or the one or more
grounding electrodes used. The bonding jumper(s) shall be
sized in accordance with Table 250.66 and installed in accordance
with 250.64(A), (B), and (E). The points of attachment
of the bonding jumper(s) shall be accessible.

If it is an electrode used, it is intentionally grounded.