Calculating the size of a 3 phase generator

[Moxy Man]

When I size a single phase unit I simply have the client turn on those tings they want to have access to during an outage and I simply take an amp draw reading. I've been doing the same thing with 3 phase. I then go to the data sheets on the generator I'm using, typically a Kohler, and find the unit that, at .8 PF, that supplies those loads.

 

[kwired]

That approach may or may not work, especially with motor driven loads. You need to be able to start the motor(s) and at least need to do such current measuring at normally expected loading levels. A machine running idle may draw a lot less than when at normal loading.

Then when dealing with three phase, you may or may not have strictly three phase loads vs single phase loads or you could have mix of single and three phase loads and possible unbalancing of the three phase supply, which could result in needing a larger capacity unit just to make sure you can handle a certain amount of unbalance.

 

[Moxy Man]

Excellent answer. Obviously a LOT to consider with 3 phase. So noted. Thank you.