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Electric motor rotation #170277 10/30/07 08:13 PM
Joined: Dec 2004
Posts: 78
Cinner Offline OP
Is the correct rotation of a motor always marked on the exterior of the motor?

Work Gear for Electricians and the Trades
Re: Electric motor rotation [Re: Cinner] #170279 10/30/07 08:24 PM
Joined: Sep 2002
Posts: 908
NORCAL Offline
IMO, the rotation should be marked on the equipment powered by the motor.

Re: Electric motor rotation [Re: NORCAL] #170300 10/30/07 10:32 PM
Joined: Jul 2002
Posts: 8,379
Trumpy Offline
In most cases yes.
Provided no-one has modified the connections in the terminal box for you.

Re: Electric motor rotation [Re: NORCAL] #170301 10/30/07 10:35 PM
Joined: Aug 2007
Posts: 853
leland Offline
Originally Posted by NORCAL
IMO, the rotation should be marked on the equipment powered by the motor.

Agreed. Motors power equipment.

Re: Electric motor rotation [Re: leland] #170352 11/01/07 12:20 PM
Joined: Jun 2007
Posts: 301
JValdes Offline
Three phase motors are NEVER marked for rotation. They are designed to go either direction. You choose the direction you need.
Pumps/fans/ect... have an arrow or some marking to allow it to operated properly.

Some applications I have worked on, call for the motor to use both directions on the same piece of equipment.

Re: Electric motor rotation [Re: JValdes] #170472 11/03/07 08:37 PM
Joined: Jul 2004
Posts: 101
jraef Offline
What good would it do to mark the motor? The motor mfgr. has no idea how you are going to hook it up or what the incoming line sequence is at your facility. ABC is relative. For instance, PG&E here in California is A-C-B with relation to other facilities in the US, but that means nothing to everyone local here. It just is what it is.

CBS: Connect it, Bump it, Swap leads if needed

Re: Electric motor rotation [Re: jraef] #170482 11/04/07 09:25 AM
Joined: Sep 2005
Posts: 421
togol Offline

just make sure the load is disconnected before bumping

some things don't like going backwards

Re: Electric motor rotation [Re: togol] #170483 11/04/07 10:04 AM
Joined: Jun 2007
Posts: 301
JValdes Offline
Correct my friend. When I supervised a motor shop some years ago, some customers would call and ask if we could mark the leads, so the motor would turn in the direction they wanted without "bumping". Of course we could not garranty rotation on three phase.
There are some phase detectors on the market that claim they can do this. But how can you know the complete facility is phased exact at every panel, disco or motor starter. I have even seen some companies try to do this. I have never found any of them to be successful.

Now, DC motors can be wired for a particular direction, but it must be a "shunt wound, compound wound or series wound motor.

Re: Electric motor rotation [Re: Cinner] #170488 11/04/07 10:38 AM
Joined: Dec 2000
Posts: 4,287
electure Offline
In my experience, 3Ø motors will rotate the way you don't want them to about 95% of the time.

They'll rotate the proper direction the other 5%. laugh

Tom has a good point....some machinery doesn't take well to being rotated backwards.

Re: Electric motor rotation [Re: electure] #170490 11/04/07 11:54 AM
Joined: Nov 2005
Posts: 823
JoeTestingEngr Offline
On the other hand, some motors work too well backwards. Our bus garages use 5 HP Red Jacket STPs in our underground storage tanks. (USTs) I always tell our electricians to check them both ways after replacement. I ask them to check static pressure and to squeeze off 10 seconds and check the flow rate. More than once, they've told me they didn't bother because it looked fine. I jumped on them about why I would waste my time asking them if I didn't feel it to be important. At least half the times, they've called back telling me that they got higher pressure and flow after switching the leads.

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