Generator

[bmaelectric]

Hello all, I am finishing a project where I have to hook up a temperary generator. The service is three phase 208/120 with phase rotation counter clockwise. My question is , do I just switch two leads of the generator to get that rotation ? or does the generator need to be set up for counter clockwise rotation?

 

[LarryFine]

Hello all, I am finishing a project where I have to hook up a temperary generator. The service is three phase 208/120 with phase rotation counter clockwise. My question is , do I just switch two leads of the generator to get that rotation ? or does the generator need to be set up for counter clockwise rotation?

Generally speaking, all you need to do is transpose two lines. The best bet is likely to power up a motor whose rotation direction is (a) easy to see and (b) non-damaging to be run backwards for a moment.

 

[kingpb]

When you say counterclockwise, the assumption is that you are saying that the order in which the phases reach a positive maximum are ABC. That sounds like your system voltage since you say "service". if your generator is designed for that same phasing, then there is not an y need to do anything, hook-up A to A, B to B, and C to C. Now, if for some reason the generator is ACB rotation, then other considerations need to be made.

I recommend a phasor or phasing diagram be completed to verify proper connection and coordination with your service and loads.

 

[LarryFine]

It sounds like he's merely asking if it's okay to match rotation electricially, instead of having to modify the generator to run backwards.

As I see it, the only thing that matters is that the motors spin the same way under generator power as they do under utility power.

My answer is: of course it is okay. Match the generator feed the easiest way: electrically. When one works, they'll all work.