Existing grounding electrode

[jimingram]

My company is upgrading a service in an existing apartment building, built in 1983. There are three wings tied together by a common hallway. The wings have ten , six, and four floors respectively. There is a separate service in each wing.

The utility water line comes into one wing and pipes out to the other wings. This water line was used as a grounding electrode in each of the wings.

We went from 1200 to 1600 amps in the middle wing to power up new rooftop A/Cs.

We were puzzled that there were two full size ground wires at the existing middle wing service. Both were 3/0 bare copper. One went outside the electrical room and attached to a nearby cold water pipe. The other went into the concrete floor.

I found an original electrical print with a detail which solved the puzzle. It showed this second wire was embedded in the slab on grade concrete floor and extended 20' past the building to a ground rod in the lawn.

Because we upgraded the service we can't use the water pipe electrode just outside the electrical room. We would have to go about 400' to the first wing to where the water enters the building.

Would the concrete encased electrode conductor be acceptable to use as a service ground? It would save a lot of work it it could be used instead of going all the way back to the first wing. It would seem to fit the requirements for a grounding electrode.

I know in 1983 it was common to use the water pipe as ground. I would guess the electrical engineer wanted a better supplemental ground than code required.

Thanks, Jim

 

[tryinghard]

Actually the water pipe electrode (250.52(A)(1)) is not a qualified electrode without a supplemental electrode additional to it, 250.53(D).

Why can?t you use the water pipe? The ground that goes into the slab on grade does not sound like a ?ufer? (CEE, 250.52(A)(3)) because it extends past the slab, a CEE remains in the foundation or footing. You could just install a couple of driven electrodes but if the water pipe is qualified by all the criteria of 250.52(A)(1) you must bond it as well.

You can use any electrode/combination of the over 7 listed in 250.52. But you must bond all that are present see 250.50.

 

[Pierre C Belarge]

The utility water line comes into one wing and pipes out to the other wings. This water line was used as a grounding electrode in each of the wings.



We were puzzled that there were two full size ground wires at the existing middle wing service. Both were 3/0 bare copper. One went outside the electrical room and attached to a nearby cold water pipe. The other went into the concrete floor.

I found an original electrical print with a detail which solved the puzzle. It showed this second wire was embedded in the slab on grade concrete floor and extended 20' past the building to a ground rod in the lawn.

Because we upgraded the service we can't use the water pipe electrode just outside the electrical room. We would have to go about 400' to the first wing to where the water enters the building.

Would the concrete encased electrode conductor be acceptable to use as a service ground? It would save a lot of work it it could be used instead of going all the way back to the first wing. It would seem to fit the requirements for a grounding electrode.

I know in 1983 it was common to use the water pipe as ground. I would guess the electrical engineer wanted a better supplemental ground than code required.

Thanks, Jim

If you mean the GEC in the concrete slab, the answer is no, as this is not one of the listed electrodes in 250.52(A).

Is the wate pipe that is installed to the separate wings run in between the buildings via an UNDER GROUND path, where the water pipe is in contact with the earth for at least 10 feet where installed between the buildings?
If not, then it looks as though you will be required to make you connection to the water pipe at the location where it enters the building as per 250.52(A)(1)
As per 250.53(D)(2) you will be required to supplement the water pipe electrode.

From your description in the OP, it sounds like you have quite the task in front of you.