Grounding SDS

[wolfpackEE]

I've got a question about complying with 250.30 grounding of separately derived systems.

I am working on a project replacing several dry-type transformers in a 4-story building. Almost none of the transformers have a grounding electrode conductor installed. To remedy this, I plan on installing a ground bar on each floor with a #3/0 GEC interconnecting them as allowed by 250.30(A)(6) and then providing the required size GEC (per T250.66) from each ground bar to each individual transformer.
(There is no accessible building steel available to ground to. This is a circa 1968 concrete building and everything is covered).

My question is: Does the #3/0 GEC have to connect to the cold water pipe within 5 feet of where it enters the building? The cold water pipe is in a very difficult spot to get to and it has an existing GEC connected to a main grounding bar in the electrical room. Can I connect my #3/0 GEC to the ground bar and be in compliance since the cold water pipe is already bonded?

This is a project on a state-owned building. The state reviewer made a comment about bonding the hot water piping also. I'm kind of at a loss there and would love some feedback on that too.

 

[infinity]

I plan on installing a ground bar on each floor with a #3/0 GEC interconnecting them as allowed by 250.30(A)(6) and then providing the required size GEC (per T250.66) from each ground bar to each individual transformer.

This is an acceptable way to do it especially in poured concrete structures. A common grounding electrode riser can be used as long as it's #3/0 or larger. The common grounding electrode conductor can be connected to the building GES at another location. What does the existing building grounding electrode system consist of? We use a ground bus in the service room to interconnect all of the electrodes including the common electrode riser.

Welcome to the forum.

 

[LarryFine]

Welcome to the forum, neighbor.

My question is: Does the #3/0 GEC have to connect to the cold water pipe within 5 feet of where it enters the building? The cold water pipe is in a very difficult spot to get to and it has an existing GEC connected to a main grounding bar in the electrical room. Can I connect my #3/0 GEC to the ground bar and be in compliance since the cold water pipe is already bonded?

I believe so, as long as the existing water-pipe conductor is large enough.

 

[augie47]

IMO, if the situation qualifies, you can use the exception to 250.68(C)(1) as reference in 250.30(A)(6) exception 2(a)(2) and connect beyond the 5ft point

 

[jaggedben]

...

My question is: Does the #3/0 GEC have to connect to the cold water pipe within 5 feet of where it enters the building?

No. That is, not if you have other options, such as connecting directly to another place on the grounding electrode system, or as discussed below. The 5ft rule merely permits the first 5ft of the water pipe to be used as a bonding jumper for the electrode system. The code does not actually require any connection there, although I've experienced at least one major AHJ overinterpret this.

The cold water pipe is in a very difficult spot to get to and it has an existing GEC connected to a main grounding bar in the electrical room. Can I connect my #3/0 GEC to the ground bar and be in compliance since the cold water and be in compliance since the cold water pipe is already bonded?

Yes, assuming the existing GEC is already compliant in the way it connects to the electrode(s). The connection would have to be irreversible or otherwise in compliance with 250.64(C).