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Service Configuration: Right or Wrong


Scott Irwin
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Calling all electical gurus.

I recently inspected a rural property that got me into a puzzling situation. The power to the property originates at a roadside power pole approx. 200 feet from the residence. A service disconnect (breaker) exists within the meterbox attached to the pole. Within the box the neutral and ground are bonded together and a ground wire is directed to a rod buried at the base of the pole. A 3-wire feed is buried to the residence, where it enters the main panel located within the garage. At this panel, the neutrals and grounds are combined and attached on the same attachment bar. A subpanel has been installed within a detached garage/workshop and it too has been fed by a 3-wire cable. Again, the neutrals and grounds are attached to the same bar.

As I have in the past, I stated the panels downstream from the service disconnect were subpanels, and as such, should have the neutrals and grounds separated.

An electrician is called out to the property (at a later date) to correct the issues I identified. Well, he states that since the main panel is greater than 150 feet from the service disconnect that the nuetral and ground should be rebonded. He also stated that since the subpanel was fed with a 3-wire feed, it too should have the neutrals and grounds rebonded.

So then, I am totally confused, since this type of configuration goes against all that I "thought" was correct.

As luck would have it, the same configuration existed at a similar property (less the sub at a detached building) I inspected yesterday. So now I am thinking, maybe I don't know everything, and there is more for me to learn regarding this type of service configuration. Please enlighten me.

Scott

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Originally posted by Scott Irwin

An electrician is called out to the property (at a later date) to correct the issues I identified. Well, he states that since the main panel is greater than 150 feet from the service disconnect that the nuetral and ground should be rebonded.

I've never heard that one before, and I'm not buying it unless someone can post NEC to that effect. Distance is irrelevent for these purposes, configuration is critical.


He also stated that since the subpanel was fed with a 3-wire feed, it too should have the neutrals and grounds rebonded.

His arguement is BS (the number of wires the first guy pulled does not determine which configuration is correct), but it's possible the detached garage can be wired in the typical 3-wire fashion. IF there are no continuous metal paths between the house and the garage (phone lines, TV cable, metal fences, concrete sidewalks with rebar, metal pipe, etc.) it can be wired like a main panel, but it must have its own proper grounding electrode (like a ground rod). If such a continuous metal path existed it would require the typical 4-wire subpanel configuration you're familiar with. When in doubt on an outbuilding, recommend the subpanel configuration on the basis of maximum safety.

Brian G.

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I haven't contracted for 7 or 8 years but I would say that I would have written them up as sub-panels. I personally don't know of any "150 foot" rule.

You could look at it this way. If the disconnect at the pole and meter had actually been a main breakered panel would you have any doubt that the panels from that point on would be sub-panels with an the grounds and neutrals unbonded.

You get out of something on a day to day basis and things start to get fuzzy in the ole memory.

I believe that my recollection is correct in this case. I must warn you though that i have been wrong before. Probably only once or twice though. Well maybe more than that. But I always meant well. Ha-Ha. (joke)

Buster

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First a disclaimer...electricity is not my strong suit.

In Central Texas we have one rural electric co-op that uses a similar set-up. The meter and main disconnect are located at a pedestal in the front yard utility easement with a three wire feeder to a service panel located on the house. In newer homes, the house panel is wired as main service panel with a main disconnect, neutral & grounds bonded and its own ground rod, etc. This I think is OK.

In older properties, the house panel is frequently wired with neutrals and grounds bonded, no main disconnect and no ground rod. I always write up the older houses saying that this is technically a subpanel and doesn't conform with my understanding of the NEC and recommend a sparky check it out and make any necessary repairs. Do one has ever argued with this write-up.

I have never been able to get a clear explanation of this, except that the utility company isn't bound by the NEC. However, the trend to a whole new main service entrance panel on the newer houses suggests to me that electricians are beginning to see it as I do.

Doug Hansen...are you out there?

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  • 4 weeks later...

Sorry for jumping into this a little late.

I come across this fairly often here in ND. My first impression was the same as yours, that it was the Main Disconnect and all others are subpanels. Farms, however, fall into a category all their own in the NEC. The breaker on the pole is called a "Distribution Point". It's strange, but the downstream panels are not wired as subpanels. It's almost as though the farm and its buildings are their own little distribution network. More info can be found in 547 of the 2002 NEC.

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To my way of thinking the set up is correct. If this is a 240V set up, you would have to have 2 hot2, a neutral and a ground to the house (4 wires) for the panel at the house to be a sub. If this is a 120V set up than I believe the panel at the house would be a sub. Just my 2 cents.

Kevin Teitel

House-Pro Inspections

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Originally posted by B Johnson

Farms, however, fall into a category all their own in the NEC.

Interesting. Looking back at the original post however, that may or may not apply. It says "rural property", which there are lots of here that are not farms (mine included).

What does the "B" stand for, Mr. Johnson?

Brian G.

Rural Boy, Not a Farm Boy [;)]

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B is for 'Boyd'

True, a rural property is not necessarily a "farm". However, it does seem to describe what Scott observed. Farm in the NEC does not appear to be classified by anything other than buildings. I'm thinking it goes back to the original use or the AHJ to make the call as to what it is defined as. All I know is it through me for a loop the first time I saw it and upon further research, I discovered it was acceptable. However, Your Mileage May Vary.

547.2 Definitions

Distribution Point. An electrical supply point from which service drops, service laterals, feeders, or branch circuits to agricultural buildings, associated farm dwelling(s), and associated buildings under single management are supplied.

FPN No. 1: Distribution points are also known as the center yard pole, meterpole or the common distribution point.

FPN No. 2: The service point as defined in Article 100 is typically at the distribution point.

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