standby generator

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mglennon

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I have a client that got a used 85kW, 208/120V generator that they want to install for emergency circuits. They have an existing distribution panel (480V) with two spare 3P breakers (100A & 200A). We want to use the 100A breaker for normal power input to the transfer switch (through a transformer of course), but I'm not sure what size transfer switch is required. I calculate the FLA of the generator at about 300A (assuming an 80% pf), but the normal power at 208V would be about 230A. How do I size the switch and the feeders?
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Re: standby generator

Why not fuse both sides at 250 amps and size the transfer switch and feeders to accomodate this.

I don't see the 300 amp number for the generator

Roger
 

charlie tuna

Senior Member
Location
Florida
Re: standby generator

wouldn't the full capacity of the generator be 236 amps at 208 volts and normal power would be 200 amps at 208 volts? seems to me a two hundred amp transfer switch would do the job... also consider changing the voltage connections of the generator for a 480 volt output, then go with a 100 amp transfer switch feeding the single transformer---might br cheaper???
 

mglennon

Member
Re: standby generator

I calculated the generator output as follows:
85kw/(1.732 x 208V x 0.8) = 295A.

I wasn't aware you could reconfigure the generator leads to get 480V - how is this done?
 

charlie tuna

Senior Member
Location
Florida
Re: standby generator

many generators have the capabilities to reconfigure the output leads to determine the generator's output voltage. check with the manufacturer. you said you designated the 100 amp breaker from the 480 volt source to provide normal power. this would be your limiting figure.
 
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