We designed an outdoor unit substation for a building. The plan reviewer mentioned 225.30 that doesn't allow more than one feeder to the building. But we only have one building and the outdoor unit substation serves the building only and there is a main service circuit breaker at secondary section. I am wondering why those manufacturers are still making outdoor unit substation if it is a code violation product. Any suggestions are welcome. Thanks.
Is an outdoor unit substation code violation
- Thread starter dahualin
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Cold Fusion
Senior Member
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David -
You left out quite a bit. Let me make some guesses:
Service is on the substation primary. So the transformer secondary is an SDS, not a service.
There is a secondary main out at the substation. There are then several (more than one) feeders going to different parts of the building.
Each feeder is small (less ampacity than the secondary main) and is protected with a single OCP at the building end.
This is a commercial building, not industrial.
So, how does this sound? Anything else that would matter?
cf
Cold Fusion
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You are almost right. In your opinion, is it a code violation? What makes it different if it is industrial building? Thanks.
Cold Fusion
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Wow - suprised me
Well, if you don't qualify under 225.30.A-E, then yes, the plans reviewer nailed it.
I suspect that AJHs are a bit more willing to agree to 225.30.E. It is easier for them to believe, "... documented safe switching procedures are established and maintained for disconnection."
Two suggestions;
1. See what you can do to qualify under 225.30.A-E.
2. Move the transformer secondary OCP over to the building. Install as switchboard at the building fed by the secondary main for OCPs for the area feeders.
cf
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Cold Fusion
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There is one other that I have seen done before. I can not vouch for the validity:
Build a covered walk way between the substation and the building. This makes them one structure. Why that would make the installation any safer, I don't know. Even if it met code, it's nothing I'd ever want my name on.
cf
Build a covered walk way between the substation and the building. This makes them one structure. Why that would make the installation any safer, I don't know. Even if it met code, it's nothing I'd ever want my name on.
cf
This is just an opinion, but I don't think one substation feeding a building was intended to be considered as "more than one building or other structure."
Again, just an opinion, but I think the intent was intended more for multiple structures that use electricity. You don't usually want multiple feeders to one building from multiple other places.
Why wouldn't you want your name on that? How is it any different than having the substation inside a room connected to the building?
I guess I personally just don't see a problem with this.
Why was the substation designed to be outside the building?
Steve
Again, just an opinion, but I think the intent was intended more for multiple structures that use electricity. You don't usually want multiple feeders to one building from multiple other places.
Why wouldn't you want your name on that? How is it any different than having the substation inside a room connected to the building?
I guess I personally just don't see a problem with this.
Why was the substation designed to be outside the building?
Steve
weressl
Esteemed Member
The manufacturing of a unit substation can not be a violation of the NEC as the NEC, only how such substation is utilized.
- Location
- Massachusetts
How far away could the substation be before you would call them separate?
Good point
I wasn't really thinking about them being the same structure. But, if the substation is down the street and turn left where the 7-11 used to be....then I think the inspector has good reason to cry foul.However, I think there also might be cases where this is a perfectly safe installation, and some common sense, or inspector discretion might be called for. An example might be where the substation is located pretty close to the building.
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- Illinois
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- retired electrician
In the plant I work in a number of them are between 50 and 100' from the building they serve and one of them is about 500' from the building. In all cases there are multiple feeders from the unit substation to the building. I see it as a technical violation of the code rules, but a safe and very common industrial installation.
Cold Fusion
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Maybe. Article 100 is pretty clear on the definition of "structure".. Most smaller stuff I have seen, like a 1000kva pad-mount with an intergal HV disconnect, has a full sized secondary run to the main building where the secondary OCP is located. Then the building has a switchboard with feeders running off to other parts of the building. There are rarely a half-dozen feeders from the pad-mount to various parts of the building.
I suspect it is cause the fire department wants one location where they can shut off the power.
Yes that too. Same reason.
It would look like I was trying to shave nickels building a marginal code compliant install. I don't like marginal. Always makes me wonder what else got shaved or "value engineered" to near un-workable
So the fire department shows up and says, "Where's the electrical disconnect?"
"Well, there are 6 scattered around this 2 acre building, or down that walkway about 145' there is a main disconnect."
Here are some guesses:
Doesn't want the 69kv primary inside of the building.
Doesn't want to put a 5mva oil filled xfm in the building.
Doesn't want to have to build a concrete xfm vault in the building.
Footprint for an outdoor mounted substation cost a lot less than heated, covered, inside footprint.
Doesn't want to install equipment to reject the heat loading from the transformer.
That's true. And the plans reviewer is calling it as 225.30 says.
And you are right about the distance. If it were 10 feet, that is a good case for a covered walkway, enclosing the secondary main, making it all one structure. But that also gets rid of the outside unlimited taps to the remote panels/switchboards.
225.30 gives methods to do what David has in mind. Just need to pick one. What the code is asking is not bad.
cf
Cold Fusion
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You completely lost me on this one.
What "gray"?
225.30 is perfectly clear. Either spend the money on a main CB at the building and a switchboard for the feeder cbs
or
meet one of 225.30.A-E
I don't see any gray.
cf
rcwilson
Senior Member
- Location
- Redmond, WA
Is a Unit Sub outside the building safer?
A unit sub has a main breaker and feeder breakers located outside the building. One reason for a single service to the building is to provide one place where all power can be removed in an emergency. If the building is on fire, being able to remove power by opening one breaker in the unit sub without going into a burning building seems safer.
A service entrance inside the building will have unprotected service entrance conductors with all of the related arc flash and other hazards. A unit sub fed building's "service" conductors (they are feeders) will be protected by the sub's Main and Feeder breakers. That gives better protection and less arc flash.
Placing a transformer and electrical equipment outside the building in a weather protected enclosure might reduce the fire hazards inside. (Assumes that electrical equipment is a fire hazard.)
A unit sub has a main breaker and feeder breakers located outside the building. One reason for a single service to the building is to provide one place where all power can be removed in an emergency. If the building is on fire, being able to remove power by opening one breaker in the unit sub without going into a burning building seems safer.
A service entrance inside the building will have unprotected service entrance conductors with all of the related arc flash and other hazards. A unit sub fed building's "service" conductors (they are feeders) will be protected by the sub's Main and Feeder breakers. That gives better protection and less arc flash.
Placing a transformer and electrical equipment outside the building in a weather protected enclosure might reduce the fire hazards inside. (Assumes that electrical equipment is a fire hazard.)
Is a SES 3' off the outside wall of a building a seperate structure ?
Some say 'yes' some say 'no', this is called 'grey' or 'gray'.
Cold Fusion
Senior Member
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Yes. If you want the two to be a single structure, build a covered walkway.
I can't help them. They need to read the book. That doesn't make it greay.
cf
cf,
The fact that SES's are installed this way every day, without covered walkways and are
inspected by officials who understand what they read in the book, and your opinion, is
proof that a gray area exists. I would like to see that area black and white in the NEC.
Cold Fusion
Senior Member
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- way north
Frank -
If you are saying that the installation of a substation as noted in post 11 as listed by Don, that installation is absolutely within code as allowed by 225.30.E.
It already is black and white.
If you are alluding to some other installation, then I have no clue as to what you are refering to.
cf
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