Residential Power Distribution

[mbrooke]

Ok, yeah I can go along with that. But take a look at 250.30(A) for SDS's. It doesn't say "premises". Then there is 250.142(B). But all that said, part X for over 1KV which "supplements an modifies...."

I still say they need to clarify what they mean by "multigrounded neutral system". I guess one could say that at a transformer bonding everything together and to the neutral and not running a EGC is the only thing it could mean, because any other permutation doesn't make sense.

Perhaps, but when a neutral is mandated to be grounded every 1/4 of a mile and at every transformer, IMHO it becomes obvious as to what they mean by MGN.

If a current carrying conductor is permitted or in this case mandated to be earthed repeatedly, nothing from an electrical theory standpoint says it can not function as a fault clearing conductor.

 

[electrofelon]

Not really. One transformer by itself is not enough to define a multigrounded neutral system. To have an MGN you need Multiple. In particular multiple transformers on a distribution line, each connected by a common metallic neutral which is grounded at each transformer and often at some intermediate poles.

I don't know, 250.184(C) says ".... Grounding shall be permitted at one or more of the following locations..." I don't see why I couldn't have one transformer with the supply neutral bonded and grounded.

I was questioning what "grounding/grounded" means in this context. Does it mean just connecting the neutral to an electrode? Bonding the neutral to the transformer? Both? Is a EGC still required? Although the writers fell into the "ground" trap on this one, they must mean bond and ground the neutral and don't run an EGC, as it wouldn't make sense to do just one or anything else. I think they should be more specific and/or add a definition for MGN.

 

[electrofelon]

Perhaps, but when a neutral is mandated to be grounded every 1/4 of a mile and at every transformer, IMHO it becomes obvious as to what they mean by MGN.

If a current carrying conductor is permitted or in this case mandated to be earthed repeatedly, nothing from an electrical theory standpoint says it can not function as a fault clearing conductor.

I think we are in agreement, I just don't like the vagueness of the language in the NEC. Adding another exception to 250.142(B) referencing 250.184(C) or an I.N. would make me stop complaining

 

[mbrooke]

I think we are in agreement, I just don't like the vagueness of the language in the NEC. Adding another exception to 250.142(B) referencing 250.184(C) or an I.N. would make me stop complaining

It would- but there are so many things that need clarifying in the NEC that it would quadruple in size. It is best to simply say what you can't do rather then what you can do.

 

[GoldDigger]

I don't know, 250.184(C) says ".... Grounding shall be permitted at one or more of the following locations..." I don't see why I couldn't have one transformer with the supply neutral bonded and grounded.

I was questioning what "grounding/grounded" means in this context. Does it mean just connecting the neutral to an electrode? Bonding the neutral to the transformer? Both? Is a EGC still required? Although the writers fell into the "ground" trap on this one, they must mean bond and ground the neutral and don't run an EGC, as it wouldn't make sense to do just one or anything else. I think they should be more specific and/or add a definition for MGN.

You can. It just would not be an MGN situation then, unless the incoming supply neutral happened to be multiply grounded at intermediate poles along the way.

 

[Sean.Day72]

Page 27 of that Long Island PA technical drawings is exactly what is going on. Loop feed transformer with a Bayonet Fuse to protect the primary and a MOV elbow for the surge arrestor. Load break switch in the transformer is isolate the homes it feeds.

Each home get s 3 Wire, 240/120 from the secondary with the main bonding jumper in the service disconnect.

 

[electrofelon]

Page 27 of that Long Island PA technical drawings is exactly what is going on. Loop feed transformer with a Bayonet Fuse to protect the primary and a MOV elbow for the surge arrestor. Load break switch in the transformer is isolate the homes it feeds.

Each home get s 3 Wire, 240/120 from the secondary with the main bonding jumper in the service disconnect.


View attachment 19723

Yup, very typical. If it was,fed from a delta system, it would look pretty much the same except the bushings would be labeled h1 and h2 instead of h1a and h1b.

 

[mbrooke]

Yup, very typical. If it was,fed from a delta system, it would look pretty much the same except the bushings would be labeled h1 and h2 instead of h1a and h1b.

You know your stuff!

Down side is you can't do feed through- thought 3 phase pads with 6 bushing are common regardless of wye or delta primary.