I have a 3 phase roof top unit I have to connect to new service. Will keeping it in phase be a problem? Will be enough to follow the a b c legs. It was attached to a different service on the same building coming off its own CT cabinate. The only thing I have ever done with 3 phase is replace breakers. I don't want to screw up my roof top unit.

Call your HVAC rep. and ask him if phase rotation is an issue. I don't think it is but verify
Before you finish...

Yes. Phasing is very important.
Please call an electrician. This is not something you want to get wrong and no place to play around if you don't know what you are doing.