tinkerbell2069
Member
Can You Apply 220.87 To Size A Generator Transfer Switch For A Generator Installation On An Existing Load And Size Switch At 200 Amps If Existing Service Is 600amps. There Is No Added Load And Maximum Demand Is 37kw.
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220.87
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bphgravity
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Consult your AHJ. In the jurisdiction that I work, any method recognized in Article 220 is approved for generator calculations...
A caveat would be location of the ATS in the system. if it will be ahead of the main, ATS will have to be Service Entrance Rated.tinkerbell2069 said:Can You Apply 220.87 To Size A Generator Transfer Switch For A Generator Installation On An Existing Load And Size Switch At 200 Amps If Existing Service Is 600amps. There Is No Added Load And Maximum Demand Is 37kw.
tinkerbell2069
Member
220.87
ats is located in front of 600 amp service disconnect it is service rated question is can a 200 amp ats feed a 600 amp service using 220.87.PE-noy said:A caveat would be location of the ATS in the system. if it will be ahead of the main, ATS will have to be Service Entrance Rated.
necnotevenclose
Senior Member
I'm confused is the generator new or existing?
tinkerbell2069
Member
generator and ats are newnecnotevenclose said:I'm confused is the generator new or existing?
necnotevenclose
Senior Member
Article 220.87 (NEC 2005) addresses adding load to an existing service. Article 220.87 states that you need either (1) year of data showing the peak demand or a 30-day meter reading. Based on that final existing load you need to add 125%. It is very important that if a meter is set that the meter has been tested and calibrated and the person setting the meter is qualified.
With regards to the generator I would first determine what loads are planned for the generator, how many steps may be best and how I plan to feed the generator. After that I would suggest utilizing a manufactures generator sizing (such as Cummins/Onan) program to determine my generator size. My ATS would be sized accordingly. But don't forget to consult your generator rep to make sure what is calculated is available.
With regards to the generator I would first determine what loads are planned for the generator, how many steps may be best and how I plan to feed the generator. After that I would suggest utilizing a manufactures generator sizing (such as Cummins/Onan) program to determine my generator size. My ATS would be sized accordingly. But don't forget to consult your generator rep to make sure what is calculated is available.
tinkerbell2069
Member
necnotevenclose said:Article 220.87 (NEC 2005) addresses adding load to an existing service. Article 220.87 states that you need either (1) year of data showing the peak demand or a 30-day meter reading. Based on that final existing load you need to add 125%. It is very important that if a meter is set that the meter has been tested and calibrated and the person setting the meter is qualified.
With regards to the generator I would first determine what loads are planned for the generator, how many steps may be best and how I plan to feed the generator. After that I would suggest utilizing a manufactures generator sizing (such as Cummins/Onan) program to determine my generator size. My ATS would be sized accordingly. But don't forget to consult your generator rep to make sure what is calculated is available.
Engineer I am talking to wants to size single family ATS switch using 220.87 and size it less then existing service witch is 400 amp. New 200 amp ATS will supply the total 400 Amp service. I tried to tell him 220.87 was for added load only and he showed me same artical in 1996 nec 220.35 that reads (For the purpose of allowing additonal loads to be connected to existing feeders and services) in 1999 nec this sentence was removed. This engineer is saying when they took this sentence out it allows you to re-size service. I appriciate any input you can give Thanks
necnotevenclose
Senior Member
tinkerbell2069 said:Engineer I am talking to wants to size single family ATS switch using 220.87 and size it less then existing service witch is 400 amp. New 200 amp ATS will supply the total 400 Amp service. I tried to tell him 220.87 was for added load only and he showed me same artical in 1996 nec 220.35 that reads (For the purpose of allowing additonal loads to be connected to existing feeders and services) in 1999 nec this sentence was removed. This engineer is saying when they took this sentence out it allows you to re-size service. I appriciate any input you can give Thanks
Talk about reading inbetween the lines or no lines at all! I'm not sure how you can feed an existing 400A service service with a 200A ATS. Even if the demand load is low now, depending on where you live it may be higher in a different season. I would suggest calling another engineer to get a second opinion.
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