Three Phase

Brad White_9

Wire it, bump the motor and check rotation. If wrong, swap the leads. I knew a sparky who swore he always got it right the first time and was silent when asked how. Damn lucky I say.

Big Ed

Anyway to tell before starting a new system if the legs are right for proper rotation ?

Techman

3 phase

Hi Ed !The answer is NO.What type of system?

Josh_10

My father-in-law works as a high voltage electrician on a Hydro-electric project here in Washington. His favorite thing to say is "if there is a 50% chance of getting the rotation right the first time than how com 90% of the time they are backwards"?

I feel like that sometimes too. A couple of months ago I had to start up a couple of turbine pumps that were about 16 feet tall. Fine but they had a clutch that prevented them from rotating backward. Of all the three phase motors I have had to bump that was the scariest! I wish that there was a way to tell! It turned out well though.



To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Perry_2

My understanding is 'yes' ; but not practical for most jobs

It is my understanding is that there are some "motor" and "Generator" analyzers out there that can determine this prior to hookup. However, they are pricy and are usually only used for very large motors (on the order of 1000 HP or more) or power plant electical generators (you would not want to have a 50 to 1500 MW + generator wired backwards and connect it to the grid.... Scratch one power plant generator (well not quite... but it could easilty cause $100 million in damage in a flash of an eye).

The previous advice to wire it, bump it, and then swap leads if it runs backwards is the most practical advice for all but very-very large industrial/power plant motors and generators.

Perry

J. Reid

If you're talking about a 3 phase rooftop unit (usually) the wild leg 220 is in the middle on the contactor and checking the fan blade direction isn't good enough because some have 110V fan motors so always check with refr. gages to verify it will burn out new comp. if not.

EBEBRATT-Ed

Yes, you can tell before firing it up. Amprobe, Greenlee, Ideal etc.

See W. W. Grainger page 860


Ed