Generator power feeds to multiple buildings

[isupowerplant]

We have several generators on campus that each feed emergency power only in 2-3 buildings at a time. I consider these multiple generator power circuits to fall under Article 225 Outside Branch Circuits and Feeders, and specifically art 225.30 (A). I also point to 225.32 Exception #1 for locating disconnecting means for the generator power circuit inside each building. I was told by another engineer that these generator circuits feeding multiple buildings are actually services and need to be installed per 230.6 and 230.70. I disagree with him and am looking for confirmation and perhaps something more specific in the code stating that the generator power feeders routing to multiple buildings are not services but outside branch circuit feeders. Please let me know what your interpretation of the code is for generator power feeders.

 

[charlie b]

The article 100 definition of ?service? includes the phrase ?serving utility.? That would tend to imply that the generator conductors are not service conductors, but rather feeder conductors. But I think the situation is not that clear. If your campus (Iowa State, by the way?) is similar to ones I have worked on, there is a utility connection at one or more large substations, and all power lines downstream of that (those) point(s) is (are) owned by the university. Nevertheless, when a medium voltage line is connected to the primary of a transformer, and when the secondary of the transformer is used as the power source to a building, the secondary conductors are treated as service conductors, and article 230 (not 225) is applied to the installation.

My take is that the generator output is a service, so long as the generator is located outside the building. But I can?t cite a specific code article that would confirm that viewpoint.

But I am left to wonder what difference it would make. The things I would have to do with the generator?s conductors (and the building?s disconnecting means, the ground rods, the overcurrent protection for the conductors, etc.) are no different, regardless of whether I call them service conductors or feeders.

One more thing: I don?t think it matters at all that the generator is serving multiple buildings or a single building. The answer to your question (whether I be right or not) would be the same.

Welcome to the forum.

 

[david luchini]

We have several generators on campus that each feed emergency power only in 2-3 buildings at a time. I consider these multiple generator power circuits to fall under Article 225 Outside Branch Circuits and Feeders, and specifically art 225.30 (A). I also point to 225.32 Exception #1 for locating disconnecting means for the generator power circuit inside each building. I was told by another engineer that these generator circuits feeding multiple buildings are actually services and need to be installed per 230.6 and 230.70. I disagree with him and am looking for confirmation and perhaps something more specific in the code stating that the generator power feeders routing to multiple buildings are not services but outside branch circuit feeders. Please let me know what your interpretation of the code is for generator power feeders.

I agree with your take. Art 230 does not apply. You have the right sections in Art 225. I don't know where you would find anything more specific than the sections you have already indicated.

 

[isupowerplant]

Thanks for the responses. The main differences to me are the allowable locations of the first disconnecting means inside a building depending on the circuit being a "service" or a "feeder". A service disconnect shall be installed nearest the point of entrance of the service conductors per 230.70 (A)(1). Unless you want to install the conductors per 230.6, the disconnecting means needs to occur the instant the service conductors are accessible inside the building. A disconnect for an outside feeder does not need to be located immediately inside the building per 225.32 Exception #1, which I would strongly argue that we meet.

 

[GoldDigger]

Thanks for the responses. The main differences to me are the allowable locations of the first disconnecting means inside a building depending on the circuit being a "service" or a "feeder". A service disconnect shall be installed nearest the point of entrance of the service conductors per 230.70 (A)(1). Unless you want to install the conductors per 230.6, the disconnecting means needs to occur the instant the service conductors are accessible inside the building. A disconnect for an outside feeder does not need to be located immediately inside the building per 225.32 Exception #1, which I would strongly argue that we meet.

I agree.
If the generator has OCPD or short circuit protection which protects the conductors involved, that makes the situation qualitatively different from the situation with a utility service where there is only short circuit protection and on overload protection. Since the service conductors are not effectively protected against heat generating overload, the code limits their penetration into the building. That concern does not apply to most generator conductors. Worst case the long term overload current available from the generator is limited by the prime mover.

 

[mjmike]

To the OP, you may want to review 700.12.B.6. Assuming you have a breaker on the generator, this shall meet the disconnect requirement of 225.31 if it is within sight of the building. You should also note, it refers to "225" article for outside branch circuits/feeders; not service.

 

[don_resqcapt19]

... If your campus (Iowa State, by the way?) is similar to ones I have worked on, there is a utility connection at one or more large substations, and all power lines downstream of that (those) point(s) is (are) owned by the university. Nevertheless, when a medium voltage line is connected to the primary of a transformer, and when the secondary of the transformer is used as the power source to a building, the secondary conductors are treated as service conductors, and article 230 (not 225) is applied to the installation. ...

Charlie,
While those conductors may be treated by the engineers and installers as service conductors, there is nothing in the code to support that idea. The medium voltage distribution and the transformers downstream of the service disconnect(s) are not covered by Article 230. Those items are covered by 215 and 225.