Generator switch size

[jvee1985]

I have a building being fed with 4/0 Aluminum quad overhead from utility transformer to a 400 Amp indoor disconnect. They purchased a 30KW generator and had another contractor tell them they could run 200 amp manual double throw to feed there shop. I am not all that versed on generators so I thought you guys maybe could help me out. If I bid this job with the 400 Amp 3 phase double throw and 2-3/0 copper runs I am going to get beat against somebody running half the size.

 

[raider1]

Is this generator used for optional stand-by?

If it is take a look at 702.5 for capacity and rating requirements. The 2008 NEC has more restrictions on capacity and ratings then the 2005 NEC.

Chris

 

[jvee1985]

Yes it is for optional stand by I will check code

 

[jimday]

what is the generator voltage? I would assume the sevice voltage is the same? A manual XFR switch cannot be used with a legally required emergency systems. per 700.6 so I would assume this is for stand-by only. Look at section 445 for requirements that apply to non-emergency generators. Make sure you size the generator feeders correctly if it does not have a unit mounted main breaker and provide a disconnecting means, 445.13 and 445.18.....

 

[RUWired]

If your going to use the transfer switch as service equipment to the 400 amp disconnect, then a 400 amp switch would be required. If your going to use it to pick up selected loads, then size it for the load being served.
Rick

 

[LarryFine]

I have a building being fed with . . . a 400 Amp indoor disconnect.
They . . . had another contractor tell them they could run 200 amp manual double throw to feed there shop.

In my opinion, the TS must be protected from O/L.

Consider that the TS is likely to be switched under load, too.