1 generator, 2 houses

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bill j

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This question involves a residential setting, a standby generator application.
If you were to try and feed two residences from one generator ( which I do
not recommend or do ) I see a few issues. First I do generators fairly
regularly. I know how to configure multiple transfer switches with one
source, with one transfer switch sensing and the rest utilizing only the
transfer circuit.
The gen is a 50 kW, floating neutral, solidly grounded/bonded at each
service . The thinking is 25kW to each residence. Both will have a standard
transfer switch feeding a small sub panel at each location. Underground
PVC run to both locations. Don?t figure voltage drop.

1. What does the local utility think about it. You are crossing property lines.
2. Are the two residences on the same utility feed. ( One guy looses power
and the other doesn?t )

3. Now the main question. Splitting the feed would require the breaker on
the gen to allow double landed conductors. After that problem is solved,
445.13 ex. would allow someone to size the conductors at 100% of
generator rated output ( not gen breaker size ). In all the great minds out
there would that mean that each run of conduit requires full sized
conductors?
Each conduit run is also capable of full fault current. So if you had a 100
amp breaker at each house panel and sized the wire accordingly and the
incoming feed went to ground before the 100 amp breaker, the grounded
conductor returning to source is undersized.
If the generator went to ground /frame the equipment ground is sized for
100 amp. Current would travel to each service bond and back to source at
generator on undersized conductors. In parallel but I don?t think that?s code.
If current traveled through utility grounded conductor, that isn?t source, but
would it trip the gen?s breaker. ( I have Mike Holts grounding vs bonding
book )
Distance has got to be too far for tap rule. ? ( 200? each )
I believe the installers intent is to size the wire to the 100 amp breakers at
each house ( plus voltage drop ).
A sign at each service is a MUST!
I would probably come out next to the generator to a 200amp RT panel and
break it up there.

I wouldn?t be asking if someone hadn?t already invested thousands $$ into
this and it is part way finished.
 
never heard of someone doing this with a generator. why can't you just put two 100 amp breakers at the generator and size the feeds to 100a to each dwelling ?(assuming this whole shabang is legit). (seems like there might be some crazy zoning issues, this one's beyond me)
 
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Maybe 3 years ago I had a customer that wanted to centrally locate a PTO powered generator on his farmstead for backup power to all the houses (his house, and the homes of his 3 children's families). When I started looking into how to pull this off, one of my first calls was to my inspector. He cautioned me that my state's Public Utilities Commission has rules on this, since he's basically setting up a small "power company", even though he's not charging his kids for the power. I looked into it a bit, and me and the customer determined that it was too much red tape to hassle with, and we put in 4 small padmount genny's; one for each home. Just a head's up, in case this sort of thing applies to you.
 
Thanks Marc -When told about the set up the very first thing I said was how does the power company feel about that. And you are crossing property lines. Everything went silent. They hadn't thought about it.
I like installs that are clean.
Anyway, any idea about the wire size questions? I posted in NEC because I am looking for a code answer here assuming the legal issues are OK.
 
Bill
I cannot see this installation as being legal, athough I cannot pinpoint where I would reference it in the NEC. I will think about it.

If it is proved to be legal, it will be another lesson learned.


Reason it may not be legal

210.25 - this may not be the reference, but then again it may. :smile:
I would think that a piece of equipment on one piece of property would not be permitted to supply power to another property.
 
Pierre C Belarge said:
Bill
210.25 - this may not be the reference, but then again it may. :smile:
Click to expand...

I don't think that applies here. We're talking about feeders, not branch circuits. In any case, the intent of 210.25 isn't being violated here, IMHO.

Pierre C Belarge said:
I would think that a piece of equipment on one piece of property would not be permitted to supply power to another property.
Click to expand...

Why not? Poco does this all the time, and so do end users- I cite my recent oilfield experience- the oil lease owner has non-poco (post-poco) primary distribution that runs across multiple properties for the purpose of stepping down (from 13200 to 480) to power the wells. What Bill is proposing (as someone else pointd out I believe) is a minipoco of sorts. There are probably zoning and/or regulatory issues here, but I don't think there is anything NEC-wise that forbids this. Like the oilfield job, there just isn't anything dealing with this situation in the Code.

I'd do this one "under the radar", (especially if it's out in the country) but that's just me. I know that's pure flame bait... go ahead and scold me... ;)
 
jerm said:
I don't think that applies here. We're talking about feeders, not branch circuits. In any case, the intent of 210.25 isn't being violated here, IMHO.



Why not? Poco does this all the time, and so do end users- I cite my recent oilfield experience- the oil lease owner has non-poco (post-poco) primary distribution that runs across multiple properties for the purpose of stepping down (from 13200 to 480) to power the wells. What Bill is proposing (as someone else pointd out I believe) is a minipoco of sorts. There are probably zoning and/or regulatory issues here, but I don't think there is anything NEC-wise that forbids this. Like the oilfield job, there just isn't anything dealing with this situation in the Code.

I'd do this one "under the radar", (especially if it's out in the country) but that's just me. I know that's pure flame bait... go ahead and scold me... ;)
Click to expand...



Jerm
You would make a good reporter...chopping up and editing what one has said to make it fit your purposes.

Sort of like your last statement in your last post. :wink:
 
All right everybody. I'm going to tell your wife to revoke your Internet privileges if someone doesn't have
an idea on how they would size the phase conductors and equipment ground for this situation.

Lets change the parameters and say this is on the same property.
It's a code question on sizing conductors.

The question is: If you fed two sets of conductors from one breaker situated ON the generator, does each
run need to be sized at 100% of genny output? Distance is 200 ft each.
Does the equipment grounding conductor need to be sized from the generator breaker? One in each PVC conduit to both locations.
In other words that's a lot of wire to deliver 1/2 the rated power of genny to each location.

If one were to do this, the right way is to set a 200 amp panel adjacent to the generator and split it up to 2 100 amp breakers.
 
bill j said:
The question is: If you fed two sets of conductors from one breaker situated ON the generator, does each
run need to be sized at 100% of genny output? .
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You betcha. There's no other way to do it. If you have a 20 amp breaker in a residential panel, and you're going two directions with it, you can't size each conductor for only 10 amps. They both have to be #12. Same with this generator. If you have a 60 amp breaker in the genny, any place you tap off without additional overcurrent protection has to be sized for at least 60 amps. Doesn't matter if that tap is in a junction box someplace 20 feet away or right on the genny breaker's load side terminals.

If you want to run smaller conductors, to assure that each dwelling only gets up to 1/2 capacity, then you'd need a small panel on the genny's load side and put breakers in that panel for each dwelling, sized for what you want to feed each dwelling with.
 
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Pierre C Belarge said:
Jerm
You would make a good reporter...chopping up and editing what one has said to make it fit your purposes.

Sort of like your last statement in your last post. :wink:
Click to expand...

Sorry about that!!! I didn't mean to re-state you in a way you didn't intend!! No offense meant!!
 
Thanks Marc. That's just what I was thinking but I thought I would run it by everyone. The reason is this is a real situation with real people involving a fair amount of money and work. I really don't want to be the bearer of bad news regarding the property line thing but I might need to. Also I wanted to verify the splitting of feeder situation. I may walk into the job being almost done and need to recommend corrections.
 
bill j said:
Thanks Marc. That's just what I was thinking but I thought I would run it by everyone. The reason is this is a real situation with real people involving a fair amount of money and work. I really don't want to be the bearer of bad news regarding the property line thing but I might need to. Also I wanted to verify the splitting of feeder situation. I may walk into the job being almost done and need to recommend corrections.
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I am glad that they are real people. :grin:


If there is a fair amount of money involved, how come you don't try to convincet them to install 2 generators?
 
Pierre C Belarge said:
If there is a fair amount of money involved, how come you don't try to convincet them to install 2 generators?
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Yeah, no kidding. If one generator out of 2 fails, at least one has power. If a single generator fails, they're both out of luck. Seems like you want to split the power 1/2 and 1/2 anyhow, so why not go with 2? If we're talking about a large amount of power, you're going to be able to source two generators less than 30kw each more easily and quickly than one large generator greater than 30kw. If you have one generator, you're going to have two ATS's anyhow.
 
Remember I am just walking into this about 85% done. The gen is set, the conduit in, transfer switches in. I haven't been to the site though. But I might be the point man to make 'er work.
About the real people thing. haha I was just making a point that I may need to go eyeball to eyeball with someone who may not be happy with what I have to say. They have spent x amount of dollars and might need to spend more. I know I know, not my problem, it needs to be done right.
But the property line thing may be the biggest issue.
 
bill j said:
But the property line thing may be the biggest issue.
Click to expand...

Be sure to let us know at least how that end works out for you, so we can cite it in case it ever comes up for any of us. ;)

I bet one 50 is cheaper than two 25's. That's probably why they went that way. Are these big houses? My parents have an 18 on their 1500~ sqft house and it's more than they need for whole-house switchover for sure. But they're on natural gas and not electric heat. Maybe that's the deal?
 
Maybe you already thought of this, but it would be a real good idea to only set the exerciser in one of the ATS's and leave the other exerciser clock turned off or disabled. I would also have both ATS's closing the start contact to the generator, in case just one house loses power. Won't hurt a thing for the house that still has power to have power "available" at the 'E' terminals in its ATS, since the house with normal power won't transfer anyhow.
 
Get this project done before the 2008 NEC takes effect in your area. 2008 Art 702 requires a generator with an ATS to be able to pick up the entire load calculated per Art 220.
 
tom baker said:
Get this project done before the 2008 NEC takes effect in your area. 2008 Art 702 requires a generator with an ATS to be able to pick up the entire load calculated per Art 220.
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I don't disagree with this section of the Code, but I find it humorous that we will see houses with a 30 kw gen set sitting next to the POCO pole wih a 15 kw pot feeding the samwe house :grin:
 
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