EGC for feeder

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jeff43222

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Minneapolis, Minnesota
I have a customer who currently has overhead service and wants it moved underground because the service drop wires are in the way of a planned sports court in his back yard. The existing run between the meter and the panel runs through the slab in the walkout basement to the panelboard deep inside. Most of the basement is finished.

My plan is to install the underground service and an outside disconnect switch, which I would then connect to the existing wires/conduit running through the slab. But I'm pretty sure there is no EGC inside the conduit (1-1/4" RGS/IMC). My reading of 250.134(A) makes me think that the conduit can serve as the EGC of the panelboard. I usually run a separate EGC, but in this case it's not too feasible.

Or am I missing something?
 
Jeff, I would say based on 250.118, the GRC or IMC that is going to be in between the disconnect and the panel would suffice as the EGC.
 
Why do you need to add an outside disconnect? Seems simpler just to have the new service lateral go to the existing meter.
 
paul32 said:
Why do you need to add an outside disconnect? Seems simpler just to have the new service lateral go to the existing meter.
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230.70(A)(1) requires the outside disconnect. The existing meter socket is going to be disconnected once the new meter socket is energized. Since the panelboard is nowhere near the point of entrance, the disconnect switch is required. "Inside nearest" is not convenient, so an outside disconnect is the way to go. Good thing I just installed one yesterday, so it's all fresh in my mind. :D
 
jeff43222 said:
230.70(A)(1) requires the outside disconnect.
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Not necessarily. Because . . .

jeff43222 said:
The existing run between the meter and the panel runs through the slab in the walkout basement to the panelboard deep inside.
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. . . 230.70(A)(1) may apply to your existing installation.

2002 NEC said:
230.6 Conductors Considered Outside the Building.
Conductors shall be considered outside of a building or other structure under any of the following conditions:

(1) Where installed under not less than 50 mm (2 in.) of concrete beneath a building or other structure

(2) Where installed within a building or other structure in a raceway that is encased in concrete or brick not less than 50 mm (2 in.) thick
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The conduit might not be considred inside the building until it emerges from the concrete floor and/or a concrete or brick wall.

jeff43222 said:
The existing meter socket is going to be disconnected once the new meter socket is energized.
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I also agree that all you should need to do is remove the overhead wiring and place the underground conduit into the same meter base. Worst case is that the existing base is not acceptable for underground feeding, and must be replaced.

I always try to leave as much of an existing installation in place, saving time and money. Besides, how would you be able to install a new meter base before removing the existing one first, since you ijntend to use the existing conduit?


By the way, I also agree that the conduit is adequate as an EGC; plus, without an outside disconnect, you need not separate the EGC's and neutrals inside. Using an outside disconnect would require this to be done, as well as relocating water bond and rod GEC connections.
 
You guys are geniuses! This is the first installation like this that I've come across, and I wasn't aware of how 230.6 would make such a huge difference. After reading through that section, I agree that the outside disconnect switch isn't needed if I leave the existing conduit and panelboard in place.

My original plan was to replace the existing meter socket anyway because it's not suitable for an underground service. I also like to reuse existing stuff if it's still serviceable, and I think it will work out just fine in this case.

I just sent e-mail to the customer and recommended just doing the meter swap and not doing the service upgrade, which was Plan B.

Thanks for the useful info! :D
 
I'm scheduled to do the job tomorrow, and I'm curious about what I might need to do in terms of grounding the system. Can I consider the RGS under the house that runs from the meter socket to the panel as the required supplemental electrode as per 250.52(A)(5)?
 
jeff43222 said:
I'm scheduled to do the job tomorrow, and I'm curious about what I might need to do in terms of grounding the system. Can I consider the RGS under the house that runs from the meter socket to the panel as the required supplemental electrode as per 250.52(A)(5)?
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Yes, unless the inspector asks to see the minimum amount of conduit in contact with the earth. You'll probably need to add a bonding bushing and jumper between the conduit and the panel's ground bus.

You probably will still need to run an electrode conductor from your driven ground to the interior panel, since it's supposed to be unbroken, unless you're allowed to land it in the exterior meter base.
 
jeff43222 said:
Can I consider the RGS under the house that runs from the meter socket to the panel as the required supplemental electrode as per 250.52(A)(5)?
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IMO no.

It would be highly unlikely that the conduit under the house meets the installation requirements of 250.53(G) to be considered an 'electrode'.
 
I just scheduled the inspection, and the inspector made a point to ask me if the grounding was up to code. Glad I ran new copper to the water main and drove a ground rod. I doubt I'd win if I argued the RGS between the meter and the panel was sufficient. My experience with this inspector is that he pays particular attention to grounding.
 
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