Service Ground Connections

[jerryb]

There seems to be more than one way to terminate Service Ground wires. If I were to look through Article 250 of the 2002 NEC, there are several sets of illustrations that show the termination of service ground conductors at the Neutral bus. Then there is a bonding jumper run to an equipment grounding bus. At this ground bus they then show the Main bonding jumper to the cabinet enclosure.

This is all fine for a residential or small commercial service but what about a larger service such 1000 or 2000 amps? For something this large I would expect all service grounding conductors to be terminated on the ground bus, and then a ?bonding jumper? from the ground bus to the neutral bus. In the case of some Ground Fault Protection Systems, this bonding jumper is where the current transformer is installed so as to monitor against current flow through the grounding conductors.

Is there an inconsistency in how the NEC shows the Ground Conductors connections?

 

[charlie]

Re: Service Ground Connections

I am not sure what the source of confusion is for proper grounding. The single point grounding concept is that the load side of the service equipment is all bonded back to the service bonding (grounding) bar. At that point, a main bonding jumper is to connect the bonding (grounding) system to the grounded service conductor at the service equipment. At this same location, a grounding electrode conductor is to be run to the water, building steel, Ufer ground, ground ring, ground rod, etc. Section 250.24(A)(4) permits the grounding electrode to be attached to either the bonding (grounding) bus or to the grounded (neutral) bus. If the service equipment has just one bus, the bonding (grounding) and grounded conductors will both be landed on the same bus. All bonding (grounding) goes back to the same point.

The ground fault return path runs from the ground fault to the service equipment, across the main bonding jumper to the grounded conductor, and back to the service transformer. The same concept applies for a separately derived system. I used the terminology "bonding system" and "bonding bar" to keep the concept simple. By the way, the grounding conductor will be changed to bonding conductor in the 2005 NEC (I think, it has passed the proposal stage with no negative votes). To answer your question, yes there are more ways than one to do any job (usually) and the Code permits both ways here, depending on the particular parameters involved.

 

[dereckbc]

Re: Service Ground Connections

I agree with Charlie. You can bring all your electrode conductors to the grounding bus, then install the MBJ to the Neutral Buss. 250.24(A)(4) permits this method and forms a SPG. Also look at exhibit 250.21 in the handbook, it also demonstrates a SPG with multiple electrodes.

The key to make it work is a Single Point Ground to the neutral.

[ February 24, 2003, 10:46 AM: Message edited by: dereckbc ]

 

[don_resqcapt19]

Re: Service Ground Connections

Charlie and Dereck are correct in their responses. I just want to make it clear that in small services where the main bonding jumper is a not a wire or busbar, that the grouning electrode conductor must be connected to the grounded conductor bus and not to the equipment grounding conductor bus, if there is one.
Don

 

[dereckbc]

Re: Service Ground Connections

Don & Charlie: Interesting point was made about SDS. If you apply 250.24(A)(4) to 250.30(A)(2) then couldn't you connect the GEC of a SDS to the grounding buss at either the SDS or first disconnecting means? I see the wording of such in 250.30(A)(2).

The reason I ask is because I have seen a lot of post saying it must be connected to the Xo or neutral in the first discconect.

 

[charlie]

Re: Service Ground Connections

If you apply 250.24(A)(4) to 250.30(A)(2) then couldn't you connect the GEC of a SDS to the grounding buss at either the SDS or first disconnecting means? I see the wording of such in 250.30(A)(2).

Yes, but not both places. This would be placing the grounding in parallel with the neutral.

 

[don_resqcapt19]

Re: Service Ground Connections

Dereck,
I don' t think the wording of 250.24(A)(4) would permit the grounding electrode conductor to be landed to a grounding bus at the SDS. If the words "service equipment" in 250.24(A)(4) include the SDS OCPD equipment, then at the OCPD, the SDS grounding electrode conductor could be landed on the grounding bus as long as the bonding jumper between the grounding bus and the grounded bus is a wire or busbar.
Don

 

[dereckbc]

Re: Service Ground Connections

Don, I agree with your assessment if the transformer is part of the "service equipment". Personally I specify the GEC to terminate to the Xo or the neutral in the first disconnect, as it is clear this method is allowed.

But I hear a lot of experienced PE's, electrical engineers, inspectors, electricians and the like say either is allowed. From my experience I have seen many transformers with the GEC connected to ground buss. It was shown in the approved drawings, and passed inspection. I find it interesting there is not a consensus among all the professionals.

 

[don_resqcapt19]

Re: Service Ground Connections

Dereck,
I don't think that I stated my position clearly in my last post. I'll try again. A SDS in not a service, so I don't think that it is permissible to land the GEC on a grounding bus at the transformer. In my opinion, if you make the GEC connection at the transformer, then you must connect it directly XO. If you make it at the SDS OCPD, then you may be permitted to connect the GEC to the grounding bus. To make the connection to the OCPD grounding bus, you have to stretch 250.24(A)(4) a bit. This section only permits the GEC to land on a grounding bus within "the service equipment". The SDS OCPD, is not "the service equipment", but I would permit the connection to be made in the SDS OCPD enclosure. I see not difference between this OCPD and "the service equipment" for this purpose.
Don Ganiere

 

[dereckbc]

Re: Service Ground Connections

Don that is what I thought you said the first time. Hope it helps others. I am thinking about making a new post just to get an idea of what other professionals think about it.

 

[tom baker]

Re: Service Ground Connections

Jerry, part of our problem in grounding is we use differnt terms than the NEC does. You state "service ground wires" but that could be:
grounding electrode conductor
grounded conductor
equipment grounding conductor
I use to skip over the definitions in my grounding and bonding class, but I don't anymore.
Part of our confusion is due to poor terminology in the NEC. We ground a recptacle?
In terms of your first post what is the serive ground wire?