Emg Gen Back Up System

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doninphx

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PHOENIX,AZ
I have to put in an emergancy gen with a transfer sw and transformer to service a 100 amp panel with about 40 amps of load on it.
Is there an easy way to find the calculations to size the generator, trans, and panel?
right now I have a 17.5 KW gen 120v/208 3 ph
 
I had temporarily moved this thread to an area accessible only to the Moderators. I had taken that action because this appeared to me to be a DIY situation. Being an engineer, I had no idea that the ?JIW? in the member?s profile meant ?Journeyman Inside Wiring.?

I am returning this tread to the active area. I offer an apology to doninphx for the delay and for the inconvenience.
 
If your load is 40A, 208V, 3 phase, then that would use 208 * 40 * sqrt(3) = 14.4 KVA. So a 17.5 KW generator sounds pretty close. I am assuming the 40A isn't one large motor...otherwise the generator might have problems starting the motor.
 
i am an electrican for 30 years+, but i was just trying to find a easier way of gathering this data. there are programs out there i understand that work well. if you dont do this offtin you kind of get rusty.

thanks for your help. don
 
doninphx said:
I have to put in an emergancy gen with a transfer sw and transformer to service a 100 amp panel with about 40 amps of load on it.
Is there an easy way to find the calculations to size the generator, trans, and panel?
right now I have a 17.5 KW gen 120v/208 3 ph
Click to expand...

Suggestion: Don't call it an "emergency" generator unless it is supplying legally required emergency loads. As you may know, you can't mix non-em loads or non-em wiring with emergency wiring. And you can't connect non-em loads to an em panel or transfer switch.

If it is not for legally required emergency loads such as em lighting, call it a standby generator.

The vendors would be happy to run the calc for you with your data, including motor HPs and non motor loads.
 
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