According to Wayne Whitney :
On 2007-04-25, Chris Lewis wrote:

According to Wayne Whitney :

I'm talking about the Grounding Electrode Conductor, which is a
separate wire that runs from the neutral/ground bar in the service
entrance to the earthing sources: Ufer ground, metallic cold water
pipe, and ground rod. Is it OK to run this conductor in the same
conduit as the feeder to my subpanel?

An electrician may correct me, but I believe that when the disconnect
is separate from the main panel, and you interconnect the neutral to
the grounding electrode in the disconnect, the main panel is treated
as a subpanel for the purposes of grounding.

Yes, that's what I plan to do. My original post was unclear because I
used the term "conduit" for a short stub leading from the crawl space
to the exterior main disconnect, not a full run between the main
disonnect and the subpanel. So my subpanel feeder and my GECs will
share the conduit stub for only a few feet before diverging to their
separate destinations.

I take it then that the GEC is going from the disconnect, thru the
stub (actually a PVC protective sleeve) and thence to the electrodes,
and _not_ following the cables to the panel?

I don't think there's a problem with that. I thought you were
running the GEC to the panel. But you're not, you're running an
ordinary (but large! ;-) grounding wire.

BTW, this raises another question. My disconnect and my subpanel are
30 feet apart. So the only ground/neutral interconnect is at the
disconnect, and the feeder for the subpanel is 4 conductors (#1/0 Al
SER since my service conductors are #2 Cu). At the main disconnect I
have a Ufer ground, a metallic water service pipe, and a driven ground
rod, all connected to the ground/neutral bus bar.

[Remember that the ground and neutral in the SER should _not_ be
interconnected in the panel.]

However, at the subpanel there is available another Ufer ground. That
is, a separate 20' length of #4 copper that is embedded in the lowest
part of the concrete foundation and hopefully tied to the rebar. In
theory this Ufer ground is interconnected with the main disconnect
Ufer ground via the network of rebar in the foundation. Is it both
useful and code-approved to attach this second Ufer to the ground bar
in the subpanel? To complicate things further, the second Ufer is
farther below grade than the first Ufer, as the subpanel is in a
basement while the disconnect abuts a crawl space.

I'd ask an inspector about that. If there's no neutral-ground
connection in the panel (there shouldn't be), you're theoretically
just making the grounding electrode system bigger, but there are
some things about "uninterrupted" connections between grounding
electrodes etc, and it's getting to the point where an inspector
might worry about ground loops or corrosion or weally weally
wierd circumstances resulting in a shock or fire hazard.

[I can't think of any easily plausible circumstances, but the
inspector is the right person for a final answer.]
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.