NEC Rules on Grounding Electrode Conductor(s)

[Wayne Whitney]

Hello,

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 ground rod.

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)?

Thanks, Wayne

[Doug Miller]

It is a Code requirement that they be run in the same conduit.

Sorry, don't know the answer to your other question.

[Wayne Whitney]

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.

Thanks, Wayne

[Doug Miller]

Of course you are -- it's the conductor that grounds the subpanel.

[RBM]

Your grounding electrode conductors go the main disconnect, not to the sub panel

[Wayne Whitney]

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?

Cheers, Wayne

[Wayne Whitney]

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?

Thanks, Wayne

[RBM]

If I'm reading you correctly, I'd just use #4 copper for the grounding electrode conductors, which don't need supplemental protection, and run them along side the conduit through the crawlspace

[Doug Miller]

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 separate.

[Wayne Whitney]

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 go ahead.

Thanks, Wayne

[Wayne Whitney]

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.

Cheers, Wayne

[RBM]

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

[Doug Miller]

Yep - concur.

[gfretwell]

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.

[Wayne Whitney]

Indeed, that is why I am going to be using PVC conduit.

Cheers, Wayne

[Chris Lewis]

According to Wayne Whitney :

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.

[Wayne Whitney]

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 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.

Cheers, Wayne

[Chris Lewis]

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.]

[Wayne Whitney]

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 separate sleeve.

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.

Cheers, Wayne