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#170277 - 10/30/07 06:13 PM Electric motor rotation
Cinner Offline

Registered: 12/01/04
Posts: 77
Loc: Kelowna, B.C., Canada
Is the correct rotation of a motor always marked on the exterior of the motor?

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#170279 - 10/30/07 06:24 PM Re: Electric motor rotation [Re: Cinner]
NORCAL Offline

Registered: 09/25/02
Posts: 805
IMO, the rotation should be marked on the equipment powered by the motor.

#170300 - 10/30/07 08:32 PM Re: Electric motor rotation [Re: NORCAL]
Trumpy Offline


Registered: 07/05/02
Posts: 8532
Loc: SI,New Zealand
In most cases yes.
Provided no-one has modified the connections in the terminal box for you.
Let's face it, these days if you're not young, you're old - Red Green grin

#170301 - 10/30/07 08:35 PM Re: Electric motor rotation [Re: NORCAL]
leland Offline

Registered: 08/20/07
Posts: 856
Loc: Lowell area, Ma. USA
 Originally Posted By: NORCAL
IMO, the rotation should be marked on the equipment powered by the motor.

Agreed. Motors power equipment.

#170352 - 11/01/07 10:20 AM Re: Electric motor rotation [Re: leland]
JValdes Offline

Registered: 06/03/07
Posts: 308
Loc: South Carolina
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.

#170472 - 11/03/07 06:37 PM Re: Electric motor rotation [Re: JValdes]
jraef Offline

Registered: 07/21/04
Posts: 90
Loc: San francisco, CA, USA
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

#170482 - 11/04/07 06:25 AM Re: Electric motor rotation [Re: jraef]
togol Offline

Registered: 09/15/05
Posts: 426
Loc: NW In. USA

just make sure the load is disconnected before bumping

some things don't like going backwards

#170483 - 11/04/07 07:04 AM Re: Electric motor rotation [Re: togol]
JValdes Offline

Registered: 06/03/07
Posts: 308
Loc: South Carolina
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.

#170488 - 11/04/07 07:38 AM Re: Electric motor rotation [Re: Cinner]
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
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%. \:D

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

#170490 - 11/04/07 08:54 AM Re: Electric motor rotation [Re: electure]
JoeTestingEngr Offline

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
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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