I'm replacing my exterior main panel with an exterior main disconnect
serving an interior subpanel, so I have a couple questions on
grounding at a residential electrical service entrance.
First, is it OK to run Grounding Electrode Conductor(s) inside the
same 2" PVC conduit as the #1/0 Al SER cable feeding my subpanel? Or
do they need to be separated? I have one conductor from a Ufer
ground, and another conductor going to the copper water service and a
Second, I understand the telephone and cable services need to be
grounded. They presently have individual little ground rods, so I
assume it would be better to interconnect them with the electrical
service grounding system. Is it better to do this inside the
electrical service entrance (at the ground/neutral bar), or outside it
(at the closest Grounding Electrode Conductor)?
Could you provide a reference? I'm aware of the code requirement that
the Equipment Grounding Conductor for a feeder be run in the same
conduit as the current carrying conductors, but I'm not talking about
the Equipment Grounding Conductor.
No, I'm not, the SER cable already has 4 wires, including an EGC.
[This is in contrast to type SE cable, which only has 3 wires, no
EGC.] These obviously will all be run together, as the NEC requires.
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?
OK, gotcha now. I'm not aware of anything prohibiting that, but I still
wouldn't do it: if you run it inside the conduit, then you wind up bringing it
into your subpanel, then out again, which is kind of a PITA. Better IMO to use
a grounding electrode large enough (4AWG?) to not require conduit, then run it
Doug Miller (alphageek at milmac dot com)
The conduit is just a stub to protect the exterior portion of the
wiring, so it's no extra distance to take the GEC through the conduit.
It's primarily a cosmetic issue, to have fewer wires visible on the
side of the house, since the main disconnect is near the front entry.
If there's nothing wrong electrically or code-wise with doing it, I'll
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.
Your (one) ground-neutral interconnect is done in the disconnect box,
and the bare wire from disconnect to panel is _not_ an GEC. Also
implying you break the neutral ground interconnect in the panel.
If on the other hand, you want to run the GEC to the panel (which
I believe is more often the case), the neutral-ground interconnect
isn't disconnected, and the bare wire (or metal conduit) going back
from the panel to the disconnect box still isn't an GEC.
The only time you'd run an GEC within conduit from the disconnect to
panel is when it enters one, and interconnects to the neutral at the
other. I'm not sure that's allowed, nor would you want to.
Age and Treachery will Triumph over Youth and Skill
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
I think this would only be allowed if the disconnect and panel are
very close to each other, and then you'd be treating the conductors
between the disconnect and the panel as service entrance conductors.
So you'd only have three wires between the disconnect and the panel.
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.
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 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.
[Remember that the ground and neutral in the SER should _not_ be
interconnected in the panel.]
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.]
Age and Treachery will Triumph over Youth and Skill
Yes, that's right, it's a protective sleeve. I did find a reference
that suggested that for purposes of lightning strikes, it is better
not to run the GEC parallel with any current carrying conductors. But
I decided that parallelling for a feet is better than having a
Right, except that the ground wire in the feeder cable would be doing
double duty as the EGC and as a bonding conductor for the grounding
electrode system. Perhaps that is not allowed.
Well, the inspector provides the final answer of what is allowed, but
doesn't necessarily know what the best practices are.
Yes, of course. I see that I haven't been clear about the geometry,
so my question was unclear. Sorry about that, let me try again:
The main disconnect is on the exterior of the house, and I'll be using
a short section of PVC conduit to connect the main disconnect to the
crawl space, to provide physical protection to the wiring. Both the
grounding electrode conductors and the subpanel feeder need to go
through the crawl space. Can I run them together in the same conduit
stub, or do I need to keep them separate?
That would work fine, but the exterior portion is right near the front
entry, so it becomes a cosmetic issue. Is there anything wrong with
running the GEC through the exterior conduit stub (with the feeder)
instead of alongside it? In the crawl space there's no conduit, just
the SER cable and the bare GECs.
I think Doug and I are seeing this the same way, which is that this conduit
is attached to either or both the sub panel and the main disconnect, which
would make it a PITA to enter and exit the enclosure. It sounds like this
is merely a sleeve, which wouldn't be attached at either end. In this case I
don't see any reason not to run them through together
The GEC is actually a transmission line, designed to handle high
frequency transients. An ungrounded metal conduit will act as a choke
and slow down the sheadding of this transient. The raceway may
actually carry more of the transient than the conductor. That is why
you see "city" hubs connecting the raceway to a ground rod.
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