3 phase motor rotation

allscott

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Jul 2004
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1,332
I've googled to no avail and I know someone on here will know.

I am hooking up a Nema 3 phase AC motor and want to know which way the motor will turn if hooked up with an ABC rotation.

I know how to reverse the motor but on this one I would like to know which was it is going to turn before I power it up.

thanks in advance.
 
At the risk of sounding stupid.....

I would think you need a scope to determine that for certain. I've never been that concerned with initial direction to take the time to find out, so I'm interested to see if there is a concrete method that is consisten across the board. When needing to know, I always bumped the motor without load connected.
 
Its a big motor and disconnecting the load would be a major pita. It wouldn't be disastarous if I bumped the load and it went the wrong way but I'd like to get it right.

I would think with a NEMA motor there should be some sort of standard as to which way the shaft will turn if hooked up ABC.
 
Thanks for that, however I can't physically turn the motor with the load connected and if I'm going to uncouple the load I might as well just bump the motor.

I just thought there would be some sort of Nema standard as to which way a motor should turn based on ABC rotation, maybe there isn't because I can't find anything.
 
one other method is hook up a small motor of the same type to see the rotation and possibly help determine which is actually phase a b or c. Then hook up the large motor the same configuration. This method however is not always quaranteed however but has helped me in the past in a similar problem
 
I think the OP may have been misunderstood.

He is not asking how to determine rotation of a circuit like with a phase rotation tester he is asking with the phasing correct A,B,C which way should the motor turn by nema standards?

I think if looking inline at the rear of the motor that it should turn clockwise if phased a,b,c.

Someone correct me if am wrong.
 
I think the OP may have been misunderstood.

He is not asking how to determine rotation of a circuit like with a phase rotation tester he is asking with the phasing correct A,B,C which way should the motor turn by nema standards?

I think if looking inline at the rear of the motor that it should turn clockwise if phased a,b,c.

Someone correct me if am wrong.

Kid

It sure would be neat to have such a standard design practice for sure. With nearly all of USA all interconnected on the grid one would think it possible to take a motor anywhere and hook it to A B and C and have it run in correct rotation, but as you have seen sometimes people do not hook up the wires correctly.


With one of the phase rotation motor rotation testers it does not take much motion of the motor to get a reading. Try turning with a pipe wrench or something. IF that does not work you just have to bite the bullet and do a short test run even if it does demand decoupling.

Just to make sure we are talking same instrument check grainger page
http://www.grainger.com/Grainger/ww...=motor+and+phase+rotation+testers&N=0&sst=All


Dan Bentler
 
Last edited:
Check your Pocket Electrical Engineering Handbook. NEMA does spec this and it is shown in this Handbook.

Don't have one? Shucks, they're free! Just ask your motor supplier, motor shop, or pipe and wire distributor. They usually are happy to stamp their name on the cover and give them away as promotional material.

The Handbook is published by EASA, Electric Apparatus Service Association. Don't confuse with Ugly Handbook which doesn't have nearly as much motor data.
 
On single phase motors on most name plates it dictates rotation direction cw or ccw depending on how it is wired.

I know this is vastly different from a 3 phase motor but the motors are tested and i would imagine on a correctly phased power source so to stamp direction cw or ccw when wired ABC from some reference point should be very easy.

As milldrone pointed out there are exceptions but those exception most likely only make 10-15% of the motors in industrial use.

Most are standard motors. Even on double shafted you could have some kind of reference point is all that i am saying. The design is not all it could be and could be improved for very little effort on the mfg behalf.
 
Call a manufacturer???

I consulted my pocket reference as DickDV suggested. I only find reference for single phase motors, which would lead me to believe that there is no such standard for 3 phase motors. That said, perhaps a call to the motor manufacturer could provide this detail, and confirm if there is a standard direction. This is an interesting question, so I'm looking forward to a definitive answer.
 
one other method is hook up a small motor of the same type to see the rotation and possibly help determine which is actually phase a b or c. Then hook up the large motor the same configuration. This method however is not always quaranteed however but has helped me in the past in a similar problem

I find this to be the best solution. Which I have used several times myself. Truely having ABC connected to ABC on the power coming into the building is usually suspect at best.

Last place I worked we went thru the entire plant and corrected each 3 phase drop so that ABC was the same in every location. Common place for phases to get crossed where distubution panels and transformers. Do not remeber where I read it, I think it was an Ugly's book but on a standard nema motor ABC produced a clockwise rotation. At the plant I mentioned earlier that is what would happen an ABC hookup would give you a clockwise rotation.
 
How was it wired before? which way did it rotate THEN? If the motor has been disassembled, (sent to the shop, rewound....) then why did you re-couple the load?... If it HASN'T, then it should rotate the same way it did before. Did someone forget to mark the leads.... or determine rotation BEFORE a rewire?

How did you get into this situation?

On a "very large motor" where disconnecting the load would be a PITA, it would SEEM that extra care would be taken to determine A,B,C, BEFORE you disconnected it..

Like other posters on here, I always uncouple the load and bump the rotation, unless I am the one who disconnected it (in which case it will be well marked) and it hasn't been to the shop.

My 2 cents,

Stationmaster
 

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