Am I right in saying that on a 200 amp. service, the main grounding conductor (#4) to the water pipe, has to come from the service disconnect and cannot come from a sub panel? The two ground rods at the service location have #6 going to them and are connected at the service disconnect of course. Thanks
Yes and no. Yes it can come from the service disconnect, no it can't come from a sub-panel. The Ground Electrode Conductor can be connected at any accessible point from the service point to the service disconnect. It can't be beyond that point. If this is a supplemental electrode it gets a little easier to connect but you still need to observe 250.66 to the service disconnect bus bar or GEC tap. I guess the question is what are you calling the primary electrode and how is it connected?
gfretwell, I guess the water line would be the primary electrode and the ground rods the secondary. I've always run the ground to the water pipe, from the the service equipment. I don't have the code section with me now, but if my memory serves me correct, It does have to come from the service equipment and not a sub panel.. Thanks again. just refreshing my memory. Had a job and wasn't thinking. Since the old existing panel had their ground wire coming from the subpanel to the water pipe, unthinkingly ( is that a word?? ) I got just enough grd. wire to do what they did. Guess I'll have to get some more wire Just wasn't thinking
I used to think the same thing, but now I'm not so sure. NEC 250.64(C) permits sections of busbars to be connected together to form a GEC. Now I'm not sure exactly what the CMP had in mind with this language, and I don't think they were thinking subpanels, but with the exception as written I think you could argue that the EGC to the subpanel is also a GEC if a ground electrode is connected to the ground bar in the subpanel. That EGC would have to be sized per 250.66 though (#4 copper on a 200A service).
Mark, I would probably go along with this if the rods (or other electrode) were connected directly to the grounded conductor between the service point and the service disconnect. I believe the rods can be the electrode if that is the way it is connected. We don't trust water pipe that much anyway, with all the plastic they use these days.