GEC & Multiple Utility Services

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Chris Hunter

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Part 1: How does the NEC view the following with respect to service grounding. A multi Tenant building has 2 or more services. Building has steel reinforced concrete foundations and precast concrete exterior walls. Interior columns are steel on concrete footings on grade. Each service is 1600 amp 277/480 volt and each is served by 4 sets of 600kcmil cu THWN. Each service is served by a separate underground utility service lateral from separate pad mounted transformers. Service disconnects are 500 feet apart. One water service serves the building. The incoming underground water service is located 1000 feet from the nearest service and 1500 feet from the other service. Water pipe is bonded to the nearest column with 3/0 cu GEC is allowed to be connected at the service disc means to any point on the grounding electrode system. 3/0 cu GEC from each service is routed overhead to the nearest building steel joist(not to steel column. Steel joists and steel beams are bolted and/or welded together to form a continuous steel structure. Building is existing so the requirement for bonding the steel in the footing is removed . Does the installation comply with NEC requirements for service grounding?

Part 2: NEC recognizes a common GEC for multiple separately derived system and for multiple service enclosures grouped at one location served by a single service lateral. Is there any provision which would allow a 3/0 GEC to be routed from the water pipe to service one disconnect and then looped to service 2 disconnect for the services noted above. I find no provision which allow tapping these services to a common GEC
 
Re: GEC & Multiple Utility Services

Nineteen people have looked at this thread without comment. There should be a law. Lurkers. :)

Part 2: I find no provision which allow tapping these services to a common GEC
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Do you find a prohibition? The NEC is a permissive document. If there isn't a prohibition, it's allowed.

In this case, the prohibition is found in 250.64(C). The GEC from a service to an electrode must be continuous. (Not having my 2005 in front of me, I believe the terminals inside the service do not qualify as the busbar described in that region of the code.

An easier solution would likely be to bond all the services to the structural metal member, and then run a bonding jumper from this to other electrodes. (See 250.53(C).)

Now, a question for you, from your profile: What's a "PM"?
 
Re: GEC & Multiple Utility Services

Chris I agree with George, the structural steel is part of the grounding electrode system and I would use that to my advantage to tie the services and grounding electrodes altogether.
 
Re: GEC & Multiple Utility Services

Take a look at

" 250.64(F). To Electrodes.
A grounding electrode conductor shall be permitted to be run to any convenient gounding electrode available in the grounding electrode system."

If you look at 250.52(A)(2)(2), it permits the steel to be bonded to the cold water to be "effectively" grounded. (I added "effectively" grounded).

So if you go to steel with the proper size GEC, and bond the steel to the cold water, you are good to go.
 
Re: GEC & Multiple Utility Services

Originally posted by Chris Hunter (via PM):
See Exhibit 250.26 The tap method of connecting grounding electrode conductors from one enclosure to another.
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I don't have access to the NEC Handbook, perhaps someone can comment on this.

My 2005's in the truck, but I'm not certain if the busbar allowed for GEC connections is permitted to be an integral component of a panelboard.

It seems to me that the busbar needs to be located very near the service.
 
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