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#95687 - 09/27/05 08:27 PM Grounding and RMC or RNMC?
kyelectric Offline
Member

Registered: 08/30/05
Posts: 64
In 250.64(C)the NEC speaks of a continuous grounding electrode conductor. Does that mean that it has to go from the neutral or ground bus unbroken all the way to the last ground rod or can it be broken for instance in the meter base where there is a connector with set screws to clamp down on it. I am running a 1 1/2" RNMC nipple from the meter base to the back of the panel so I don't have to use bonding bushings but the meter base has a place for the ground to connect to, does it have to connect there without being broken?

Also, I heard tonight from a electrical service provider in my area that I could use RNMC for the weatherhead and the conduit down to the meter base. But, it can only be used when the conduit does not entend through the roof. Is anyone using this for overhead service or just for temp service?

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#95688 - 09/27/05 09:29 PM Re: Grounding and RMC or RNMC?
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
You only need to attach the GEC at one place, anywhere from the service point to the service disconnect enclosure.
Attaching it twice will probably create a parallel neutral situation.
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Greg Fretwell

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#95689 - 09/27/05 10:53 PM Re: Grounding and RMC or RNMC?
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
 Quote:
250.142B Exception No. 2 It shall be permissible to ground meter enclosures by connection to the grounded circuit conductor on the load side of the service disconnect if
(a) No service ground-fault protection is installed, and
(b) All meter enclosures are located near the service disconnecting means, and
(c) The size of the grounded circuit conductor is not smaller than the size specified in Table 250.122 for equipment grounding conductors.


The word "near" is kind of open for interpitation... But you might notice that many neutral bars in meters are mounted directly to the can. Some places don't allow a GEC inside the can, and this is how it gets grounded. Many POCO's seem to have different rules about this, from what i can tell from other posts on the topic. If that exception is allowed where you are, there be no need to bring the GEC to the meter.

As for the question about 250.64C, it gets answered in E.

Where I am only RMC is allowed for service conductors, and would be bonded at both ends.
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Mark Heller
"Well - I oughta....." -Jackie Gleason

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#95690 - 09/28/05 05:50 AM Re: Grounding and RMC or RNMC?
kyelectric Offline
Member

Registered: 08/30/05
Posts: 64
I am planning on running the GEC from the grounding bar in the can through the RNMC 1 1/2" nipple and then attach the GEC to the connector on the meter base that has a clamp at both ends. Then install the ground rods and bring the other end back into the meter base and attach it to the meter base. Does this sound ok?

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#95691 - 09/28/05 07:35 AM Re: Grounding and RMC or RNMC?
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
It sounds as though you are creating parallel neutral paths if I understand you correctly.

The GEC connection should only be at one location, this can either be in the Meter Can or the Main Disconnect or Panel.

Between the Meter and the Main enclosure you will only have the Neutral and the ungrounded conductors, you will not run the GEC or an EGC in your 1.5" RNMC nipple. The installation should look like the drawing below, although you could move the GEC to the Panel if your local POCO doesn't allow the connection in the meter.



Roger

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#95692 - 09/28/05 08:36 AM Re: Grounding and RMC or RNMC?
markp Offline
Member

Registered: 04/12/04
Posts: 60
Loc: Kent, WA, USA
There are some rules that help explain why Roger's answer is correct. The nuetral is allowed to be a dual purpose grounded and grounding conductor on the line side of the service (250.142 I think). Your GEC comes off this wire at some point -- can be at the main disconnect, can be at the meter base, or it can even be at the weatherhead if you want. Everything else in the service that is supposed to be grounded is allowed to be grounded via the neutral, spliced in bus bars or not.
_________________________
Mark
Kent, WA

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#95693 - 09/29/05 07:20 AM Re: Grounding and RMC or RNMC?
kyelectric Offline
Member

Registered: 08/30/05
Posts: 64
I talked to a local inspector yesterday. Thanks for all the replies, you guys are exactly right. There are only 3 conductors that pass through the nipple and into the panel. One the meter base there is a small lug beside the neutral lug. They are connected and the small lug is for a #4 or #6 GEC to connect to and go out to the grouding rods. Thats why I joined this forum!!! Thanks.

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