Two buildings connected for about 10 corner to corner. Service laterals to each from a single pad mounted transformer. 120/240V-1 Ph. Multi family with separate meters at the buildings. Essentially the two buildings are separate buildings except that they share a water service (the water service & meter is in one and the copper water main runs to the other)
Should just the one building service ground be connected to the underground water service?

Sounds like there are two (2) electrical services. Two (2) main disconnects, 1 at each, or the good old six switch rule at each. So each has to be grounded at the respective first means of disconnect to the water, steel, rods, etc.

Yes. Two services/two main disconnects (1 each). But only one water.
Just ground the other one to a ground rod only. I don't think both should be connected to the water?

I would say since the building is connected that the 2nd service grounding electrode conductor should be connected to the waterpipe within 5ft of its entry to the structure...250.50 + 250.68(C)(1)

I hear you but that is the same as connecting the ground for the two services together. Is this OK?

IF you have water pipe that is in contact with the earth, it must be connected to the grounding electrode system.

Think about this....a bunch of structures all connected with metallic water services; all tied into a metallic water 'main' in the street. That equates to many services all connected to what in actuality is a 'common electrode'!

You certainly want all of the grounding electrodes bonded together and the water pipe is as good a way as any. Does the pipe run underground between buildings? Connect the second service to the water pipe within 5' of it's entrance to that building. You still need another electrode in both buildings. Water pipes can not be the only electrode.

On second thought cgw...if the building you are working in has a true Fire Wall separating the structures, they are considered separate buildings and each would need its own grounding electrode system. You would still need to BOND the water pipe system in the 2nd building. (if it were metal)

The fact that you have 2 services to the building must have been allowed because of Fire Wall separation?

I say you are allowed to ground to the water pipe in the 2nd building but not required. Better ask the AHJ what he thinks also.

I agree with John and Greg: there are Two Separate Services, therefore each Service requires a Grounding Electrode System.

Since there is a Metallic Water Line with minimum 10 feet direct contact with the Earth, this Metallic Pipe must be included in the Grounding Electrode System.

In addition, per 250.53(D)(2), the Cold Water Electrode must be supplemented by at least (1) additional Electrode (typically driven rods or "Ufer").



This may require the Grounding Electrode Conductors bonding to the Cold Water Line at the same location (i.e.: both terminate within 5 feet of entrance to the Building), unless the Cold Water Line entering the "Other Building" (the Building without the Water Meter) could be figured as if it was coming in from the Street (min. 10 feet contact with Earth).

Sounds to me that the GEC from both Services will need to Terminate at the same location on the Cold Water Line (within 5 feet from entrance to the Building).
There will only need to be (1) Supplemental Electrode(s) to the Cold Water.

Does this sound right???

--Scott (EE)

Scott:
As I 'see' the OPs layout; two (2) electric services, and one (1) water meter, with metallic water pipe to the second structure.

A GEC to the street side of the water pipe, with a jumper around the water meter bonds all the metallic water piping, both within that structure, and over to the adjacent structure. A GEC on the water pipe in the second structure would bond that service to the GE, along with whatever additional GEs the OP cares to install.

I see no reason to run the GEC from the second location back to the street side of the water meter.

Agree? Or debate?

John...I agree with your comment...

The reason for connection of the GEC within 5ft of its entry to the building is that there is less likely a chance that changes in the water pipe system to other than metallic will happen there than downstream from that point.

Once again I will say that if there is a real FIRE WALL separation between the 2 units they are considered separate buildings and a grounding electrode conductor connection at the building with the water pipe entry would NOT be required from the building without the water pipe entry from the street.

They are separate buildings with the fire wall period.

In my 9th edition of Soares Book on Grounding page 236 figure 13-10 depicts this same scenario.

Separate Buildings=Separate Grounding Electrode Systems.

Does the water pipe go back in the ground between buildings?

Shortcircuit:

OK two structures that are joined, but separated by a real firewall, makes then individual structures. We agree on that.

The water pipe from one building to the other, IMHO is the same thing as IF this is a water service from the street, IF it is in the ground between structures. The fact that there is only one water meter is irrelevant IMHO.

I do not have a Soares Book.

Also, the water piping system must be bonded to the GEC system in the structure, so is this a moot point???

This is where I see the difference between Bonding the GEC's at One point, or each GEC Bonded at separate locations: if the Second Building is fed via an Earthed Cold Water Line, or is it fed via a Cold Water Line mounted on hangers.

The latter (Cold Water Line mounted on hangers) seems more likely of an Installation; as it is the norm for most Projects I have had the pleasure to contend with.

So, IMHO, if the Cold Water Line to the Second Building / Service is installed >10 Feet in the Ground (Earthed), then termination of the GEC within 5 Feet of the point where it comes out of the Ground would be compliant - with Supplemental Electrode(s) Bonded to the Second Location as well as the First Location; otherwise, the GEC from the Second Service would need to be run to the POE (Point Of Entrance).

Does this sound right, or am I missing the point???
(or should I wear a Hat, to "Cover My Point" )

--Scott (EE)

Scott35

Yes, we agree, and you are not missing the point.

No hat needed.

The area that the OP is from tends to influence me to lean to an earthed water line, well below a frost line.

The ultimate answer depends on the OP responding IF the water pipe is earthed. There are many scenarios that the pipe could be installed from point to point.

---BUMP---


Whazzup with this topic???
(i.e.: did this thread answer the OP's question/s???)

--Scott (EE)

Sometimes....ya never know!

LOL!!!

Scott,
The OP hasn't been here since he posted this topic.

I guess the OP is using Mental Telepathy to view the Replies in this Thread!!!

--Scott (EE)