Generator

[tdv]

I have a question about ATS/Generator. Hope you guys can help.

My client wanted to install an ATS for a future lease propane generator. It's 240V/3PH service. I've never done this before and I am not sure what exactly need to be done. Do I need to provide any special connector for future generator connection? The contractor told me that it requires a special hook up because of the 'high leg'. Not sure what else I need to show on my one-line.

thanks

 

[augie47]

How much is provided seems more a "contractual" decision than a NEC one.
Things to keep in mind:
(a) The ATS must be "service rated" if it is installed ahead of your service disconnect.
(b)The ATS & Generator must be capable of carrying the designed load
(702.15)
(c) The generator supply must have disconnecting means at the building or meet 702.11.

Locally, what I see most often is a ATS with the generator wiring terminated in an outside disconnect switch or a "inlet" for generator cord.

 

[ceb58]

Agreeing with what Gus has said. I would ask for some more info. on exactly what you mean by

a future lease propane generator

Is this a unit that will be brought in before or during an outage and then taken away later?

 

[tdv]

Yes, that generator will be brought in and taken away later. I connected a Generator terminal box to the ATS for future use. That's all I need, right? I am not sure why the contractor mentioned about the "high leg". The service is 240/3PH, they can bring in a 240/3PH generator and connect to the terminal box. I just want to get some opinions before asking the contractor about it. He said he has already installed one in the past and it's not simple as I proposed above.

thanks

 

[Electric-Light]

Yes, that generator will be brought in and taken away later. I connected a Generator terminal box to the ATS for future use. That's all I need, right? I am not sure why the contractor mentioned about the "high leg". The service is 240/3PH, they can bring in a 240/3PH generator and connect to the terminal box. I just want to get some opinions before asking the contractor about it. He said he has already installed one in the past and it's not simple as I proposed above.

thanks

Generators often offer various output configurations, such as 240v delta with no CT, 208Y/120, etc. If the utility provide 240/120 delta with high leg, the 120v loads will be hooked up between the center tap and the two phases except the high leg.

3 phase motor loads will rotate the correction direction as long as the phase rotation is correct, but if the relationship between the legs and the center tap is incorrect, 120v stuff on one of the legs will get fried from getting fed 208v.

 

[augie47]

Yes, that generator will be brought in and taken away later. I connected a Generator terminal box to the ATS for future use. That's all I need, right? I am not sure why the contractor mentioned about the "high leg". The service is 240/3PH, they can bring in a 240/3PH generator and connect to the terminal box. I just want to get some opinions before asking the contractor about it. He said he has already installed one in the past and it's not simple as I proposed above.

thanks

It's possibly a grey area since the generator is not on site and some info can't be obtained, but I would be inclined to require a disconnect per 225.31 and 225.32. If it is a 240 hi-leg service, he should comply with 110.15 and the system should comply with the requirements of Art 702 including 702.8

 

[ceb58]

Another item the OP did not state is what size amp service he is working with. In this case I think I would go with a service rated manual transfer switch. There may be long periods of time when the ATS is not transferred. Some times the electronics will go bad from not being used or they could take damage from surges or strikes. The problems may not show up until the ATS is needed and then it will not work properly.

 

[kwired]

... The problems may not show up until the ATS is needed and then it will not work properly.

Which also gets me thinking what is the point of an ATS if there is no power source to transfer to. If the generator is only brought in when needed why not transfer power when needed also?

 

[tdv]

The service is 400A and I provided a service rated manual transfer switch for the future generator. I didn't see anything wrong with the design and I wondered what the contractor had in his mind. Thanks all.