ECN Forum Forums Code Related Discussion NEC & other Code issues 250.32(B)(1) 2005 NEC

There is quite a bit of current flowing through the ground, particularly in wye distribution.

I always insist on fiber optic between buildings, for the data connections.

But there has for a long time been issues with shared metallic paths between buildings with separate services (e.g. a neighborhood of homes on the same metal water pipe, cable TV coax, etc). If one of them loses neutral on the service drop, guess what gets to carry the difference (and all along it was carrying a fraction of it, anyway). I'd rather my water and gas come in on plastic piping, and the phone/TV/internet come in by fiber or RF, just to avoid those issues. Eventually, I'll get it arranged that way (it was hard enough just getting the cable company to properly ground their stuff).

Here's a fun one to consider:

Utility service drop comes to the house. A whole house (25kVA or more) generator is inside the separate detached (and powered) garage. How can you wire up so the house is powered by the generator, and not only comply with 250.32(B)(1) but also be sure the proper transfer(s) exists.

You are going to have problems any time you put a generator on the other side of the garage unless you feed it all the way back to the service.

No matter how you do it, I don't see any way to avoid TWO runs. There is just no safe way to share a single run and switch directions on it. But how to avoid grounding loops in that? Either the generator is isolated from the garage completely, or you have two transfer switches (with neutral transfer). But does it have a single EGC?

Just stuff to think about (when you have time to think about weird things).

You never switch the EGC and it can be tied to earth as many times as you want. The only issue is where it gets bonded to the neutral.

I am still not sure how you could coordinate two transfer switches in a compliant way. You really need to bring the generator feed back to the service entrance.

I certainly would not switch the EGC. I'm just wondering if there might be issues with having 2 or more parallel EGCs. For example, existing conduit is filled with power from house to garage. If adding the generator at garage to feed to the house (whether generator to garage power takes it directly at the garage, or lets it loop first through the house), does one need to abandon/replace the existing conduit, so that the new conductors, as well as the old (though possibly replaced to physically new), can both be run immediately adjacent to a single common EGC. Or can they be separate with duplicate EGC which might be interconnected on both ends forming its own loop (but in any case, any fault currents would certainly run parallel in both conduits if set up like that ... plus over the cable TV coax, wtx, so that's not really a solved issue)?

It seems to me (I didn't try to look this up) the correct way is one conduit big enough for all this, 3 conductors for house to garage, 3 conductors for garage/generator to house, and 1 EGC (change 3 to 4 for 3ph where that might happen to be).

Also, it seems to me that if multiple EGC connected together at each end is not a good thing, then letting TV coax shield be wired the same way is also not a good thing.

We have multiple EGCs all the time. Every time you pull a green wire in a pipe you have a parallel EGC and the HCF rules even require it.
As far as the code is concerned ground is ground and the more the better. If we have multiple circuits passing through a J box, don't we bond all of the EGCs together? We reground the EGC pretty much any time we can (generator frames, additional buildings etc).

We do get concerned with the neutral.