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#196479 - 10/08/10 12:01 AM 3 or 4 wire service??  
Merlin  Offline
Joined: Jan 2004
Posts: 170
NW Indiana
Ok, so this may sound crazy but I am fighting myself on this. I am wiring a new house and am questioning myself on the service. I normally install meter and main panel back to back. But this one I cannot. I will be installing meter on outside of one wall and the panel will be inside (approx. 5 feet away) on adjacent wall. Therfore I will be running SE (or SER)cable between the two. When installed back to back, I always run 3 wires plus ground. I normally run bare ground from ground rods through meter base and continue to main panel. Since I will be using SE cable is this necessary? If I bond at the meter and bond the neutral bar at the panel with bonding screw, do I need to still run ground to it. It would difficult to do this continuousley with one piece. Can I use SE 3 wire and bond at panel with bonding screw or do I need to use SER 4 wire?

Thanks for clearing this up.

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#196480 - 10/08/10 12:40 AM Re: 3 or 4 wire service?? [Re: Merlin]  
wire_twister  Offline
Joined: Jul 2007
Posts: 265
Georgia USA
This is an AHJ call, in my neck of the woods you only need 3 conductors L1-L2-N as long as the load center is a "reasonable distance" from the meter. When I pressed him (the AHJ) on the distance he said less than 15 feet. Anything over 15 feet requires a main disconnect on the outside of the building and 4 conductors L1-L2-N-G to the load center. All these conductors must be insulated, even the EGC. The reason he gave me was to limit the length of unfused/unbreakered service conductors inside the building. So to answer the question 3 wires and a bonded neutral in the meter, and load center would be fine here.


Life is tough, Life is tougher when you are stupid

#196482 - 10/08/10 10:48 AM Re: 3 or 4 wire service?? [Re: wire_twister]  
harold endean  Offline
Joined: Feb 2002
Posts: 2,233
Boonton, NJ

I would agree with Jimmy, that it is an AHJ call. The NEC (I believe) says, the disconnect has got to be "AS SOON AS POSSIBLE." (I don't have my code book with me.) So how soon is that? Some say 3' some say 5' some say 15'. Each job is different. Will the "back to back" be subject to damage? Then you might want a disconnect outside and run a 4 wire to the service which becomes a sub panel to protect the conductors. Or you might have to install the back to back in pipe to prevent damage.

#196490 - 10/08/10 02:16 PM Re: 3 or 4 wire service?? [Re: harold endean]  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,809
Brick, NJ USA
I agree with Jimmy to a point.

The "15'" is a call by that AHJ, not an NEC mandate. There is no measurement within the NEC, an item which has won me many a bet!

IMHO, an exterior meter, with conductors entering above the sill plate, and going straight down to an interior MCB panel is compliant, irregardless of the basement ceiling height. However, locate said MCB panel a distance to the right or left of point of entry...that's a problem.


#196492 - 10/08/10 03:18 PM Re: 3 or 4 wire service?? [Re: HotLine1]  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
There's a few issues here, and no 'set' answer.

First is: where do you bond the neutral to the GEC? Well, depending on your meter base (or, for multiple meters, your main disconnect), it's very possible that it will at some point BEFORE your panel.

Why? Because some meter bases bond the neutral to the case, as do some discos. It seems to me that, when this is the case, that here is where the GEC should go.

In Reno the use of the "All-in-one" is nearly universal, and this issue doesn't arise. Here in Arkansas, it's a different story. Most services I've seen have NO main disconnect, no matter how many circuits there are. Nor is the panel located anywhere near the meter. Fortunately (?) the use of SER is nearly universal, so the issue of 'parallel paths' between the panel and the meter is avoided.

If someone is going to have the meter outside and the panel inside, I think the "Chicago" model is the way to go: disconnect outside, pipe to the panel, panel located very close to the meter. I'll leave it to someone who's been to Chicago more recently than I to tell us how they treat the neutral / GEC / ground bond.

#196494 - 10/08/10 03:35 PM Re: 3 or 4 wire service?? [Re: renosteinke]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,069
The NEC softened the language about parallel neutrals and rebonding the neutral in that area between the meter base and the service disconnect, understanding that the utility is always going to bond in the meter base. It was the only way to allow a metal SE raceway and still allow bonding in the disconnect enclosure like 250 says we have to do.
The other issue we saw was where you land the GEC. They fixed that too. It can be anywhere from the disconnect can to the service point.
The only thing they left hanging is what " inside nearest the point of entrance of the service conductors." means in 230.70.
The AHJ is the only one who can answer that and it is anything from a flexible answer to "X" feet/inches, no exceptions.
We have one AHJ here who says, on a piling house, you need a ground level disconnect, no matter what and another one is "within 5 feet or so of entry to the house" even if the SE cable ends up being 50' long snaking all around (~45 feet outside).

Greg Fretwell

#196516 - 10/10/10 10:55 AM Re: 3 or 4 wire service?? [Re: gfretwell]  
Merlin  Offline
Joined: Jan 2004
Posts: 170
NW Indiana
Thanks for the information, Gentlemen. That was what I was leaning towards, but wanted to be sure. The AHJ that I deal with is rather reasonable to agree with. Thanks again for putting my mind at ease.

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