40KW 3P 208V Generator question.....

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chevyx92

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VA BCH, VA
A 3P, 120/208V, 40KW, 0.8 PF, 60HZ at 1800 RPM generator has a calculated AMP output of 139A. The generator has a factory installed 150A molded case circuit breaker rated at 100 % in it and comes with an ATS rated for 200A. My question is: Do I size the conductors for the 139A or size them to the 150A breaker? Also why can they install 150A breaker to protect the generator when 139A is the rated output? And if I have to size to the 150A breaker, does that mean I can set a 150A panel with main breaker in it? It's a little confusing because with the 139A output, I wouldn't think you be allowed to have a load rated higher than that. What am I missing?
 
Not sure for sizing the wire it is going to make a difference.

You won't be able to use #1 Cu it is only rated 130 amps at 75 degree
That makes the 1/0 Cu at 150 amps, the only option that I see.

We would set the 150amp panel and limit the loads in it and use the 1/0 Cu
 
chevyx92 said:
A 3P, 120/208V, 40KW, 0.8 PF, 60HZ at 1800 RPM generator has a calculated AMP output of 139A. The generator has a factory installed 150A molded case circuit breaker rated at 100 % in it and comes with an ATS rated for 200A. My question is: Do I size the conductors for the 139A or size them to the 150A breaker? Also why can they install 150A breaker to protect the generator when 139A is the rated output? And if I have to size to the 150A breaker, does that mean I can set a 150A panel with main breaker in it? It's a little confusing because with the 139A output, I wouldn't think you be allowed to have a load rated higher than that. What am I missing?
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JMNSHO

If the generator has a 150A CB in it, you can install a MLO 150A (or more) panelboard. It can also have a main brekaer, but is not required. In either case, the feeder or main breaker protects the panelboard bus.

The feeder minimum conductor size has to be sized to the actual load, not the capacity of the generator.

As a practical matter, I would run 1/0 copper and not worry about it. The next size down is #1 and it is only good for 130 Amps.

Just curious, how did you come up with the 139 Amp number? I would be looking at the nameplate.
 
petersonra said:
JMNSHO

If the generator has a 150A CB in it, you can install a MLO 150A (or more) panelboard. It can also have a main brekaer, but is not required. In either case, the feeder or main breaker protects the panelboard bus.

The feeder minimum conductor size has to be sized to the actual load, not the capacity of the generator.

As a practical matter, I would run 1/0 copper and not worry about it. The next size down is #1 and it is only good for 130 Amps.

Just curious, how did you come up with the 139 Amp number? I would be looking at the nameplate.
Click to expand...

139A is what is on the specs from CAT. Plus if you calculate it that's what it comes out to be with a 80% power factor figured in.
 
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