Electric motor run direction questions and answers:
Frequently-asked questions about the cause of & repair for electric motors that run backwards.
This article series describes A/C electrical motor troubleshooting: here we provide an electric motor diagnostic table, a troubleshooting guide that helps diagnose and repair most electric motor problems for motors found on HVAC equipment in buildings such as air conditioners, furnace or air handler blower fans, oil burner motors, well pumps, and condensate return pumps.
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Questions & answers about the run direction of electric motors & why a motor might run backwards, posted originally at ELECTRIC MOTOR RUN DIRECTION
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An electric motor will not normally run on either 115V or 230V "hooked up the same way" - so we are missing something here. I suspect you have an older motor that achieves 230V operation by wiring two individual 115V windings in series or in parallel to swap between.
Your motor is probably from the Master Electric Co., in Dayton OH and would have been made before 1963.
Our illustrations of Master Electric Motors, Master Electric Motor Data Tags, and Reliance Electric Duty Master A-C Motor data tags shown here may be for different motor models than yours but they will provide examples for other readers.
Shown above: a Master Electric Company (Dayton OH USA) electric motor ca 1960. This motor can be wired to run on 115VAC or 130 VAC single phase current, as you can just make out on its data tag given below.
[Click to enlarge any image] Shown below: the data tag for this motor.
Here's the first thing to check: how many wires are coming off of the motor windings?
4 wires off of the windings means you can probably swap motor direction.
3 wires off of the windings means you cannot swap motor direction since 1 of those 3 is feeding both start and run windings.
Modern electric motors with more-current data tags will tell you right on the data tag that the motor run direction is reversible or not.
For example a non-reversible motor data tag might include this text: MOTOR IS NON-REVERSIBLE, CCW ROTATION SHAFT END.
For a motor that IS reversible a modern tag will usually give specific directions for reversing its direction, (usually swapping red and black wires) such as these examples (Warning: your motor will probably be different)
But on a 3hp motor it's probably not quite that simple. Your motor may have both a start winding and a separate "run" winding.
The winding with the smaller gauge or "thinner" wire will be the Start winding and that winding will be electrically in series with the start or S terminal on the motor's start/run capacitor or will be connected to a separate starting capacitor on motors that use two separate caps.
You can also identify the start winding and run winding wires by measuring the resistance of that circuit.
The start winding will always have a much higher resistance (typically about 6 Ohms on small motors, or about 3x the run winding) than the run winding (typically about 1.5 Ohms on small motors) when measured using a VOM or DMM in the OHMS or Resistance setting.
Keep in mind that you cannot properly measure a coil winding resistance unless the wire ends are disconnected from the rest of the motor wiring.
On that motor type a centrifugal switch opens or turns "off" the start winding current once the motor is up to speed.
I would prefer not to try swapping the direction of a motor using a start winding before you find the actual wiring diagram (or figure it out) for the specific motor. But generally what you'd do is swap directions of the wires bringing current to the start winding.
While I have not (yet) found the exact wiring diagram for your motor, here INSTALLATION, OPERATION AND MAINTENANCE OF RELIANCE® STANDARD INDUSTRIAL AC INDUCTION MOTORS - PDF is a book of wiring diagrams for the same series of motors when produced later under Baldor - as I'll explain in a historical note below.
Below: Older 1/2hp 1725 / 1425 RPM 3-phase electric motor and data tag from Master Alternating Current Motors, Master AC Motor Style 23721 7E
Also see more about data tags at ELECTRIC MOTOR DATA TAG
You will find electric motors from this company labelled as
Master Alternating Current, Mater Electric Co., Dayton Ohio USA
and also as
The Master Electric Company was founded in 1920 and headquartered in Dayton, Ohio by Everett Larsh.
The company built electric motors, electric gear-motors, motor controls and motor brakes. They supplied private industry as well as the U.S. government.
In 1958 the company merged with Reliance Electric Company Reliance Electric Company of Cleveland, Ohio. Master's headquarters and plant in Dayton were closed in 1961 and moved to Columbus, Indiana.
Reliance bought ... Master [Electric AC Motors] in 1963 and [the Master Electric Company] ceased to exist.
... In 1982, Reliance moved its headquarters to Greenville, South Carolina... [and] was purchased by Rockwell International in December 1994, ... acquired in turn by the Baldor Electric Company 2007. - retrieved 2017/10/14, original source: vintagemachinery.org/ mfgindex/detail.aspx?id=3320
[Use the page top or bottom CONTACT link to send me photos of the motor and its data tag and I can comment further].
On 2017-10-14 by Victor
I have a very old Masters AC single phase 3hp motor that will run on 115v or 230v each hooked up the same way.
The motor runs clockwise and there is no indication on the tag if it can run CCW
The is only 4 wires coming out of the motor Black, Gray, Yellow, Red.
Yellow and Red are tied together for both 115v and 230v. while Black and Gray are hooked up to the power source along with a Green wire that is secured to a screw and does not come out from the inside of the motor.
Question is Can I swap either black or gray with either yellow or red to have the motor run CCW?
This is on the tag and I can't seem to find any information about this motor Thanks in advance.
On 2017-06-09 by (mod) re: why would a shop fan motor run backwards in higher gear
I agree that's a curious question. I but can guess that we've got one of the "motor runs backwards" causes listed in the article above like a bad start capacitor AND perhaps a shorted motor winding that are taken out of the circuit once the motor gets up to speed in the higher gear.
On 2017-06-09 by loveel
What makes a shop fan run in opposite direction in 1st&2nd gear and start smoking, but run in right direction in 3rd gear fine
On 2017-05-0 by Qahtan Al-zaidi
Thank you for the explanation. It is really helpful in diagnosing such a.c motor faults
On 2017-03-19 by (mod) re: motor run direction stamped on a Beckett oil burner motor
Thanks for the comment, that will help other readers.
Indeed while from the factory we'd expect all of the oil burner components to be correct, at BLOWER FAN ASSEMBLY CLEANING http://inspectapedia.com/aircond/Air-Handler-Blower-Cleaning.php we include an example of how easy it might be for a technician to install a squirrel cage fan backwards with respect to its drive motor shaft - it'll spin fine but it wont' deliver air in that position.
On 2017-03-19 by Colette
@Dan mcallister, yes, you are correct. On my Beckett, it has an arrow indicating a CCW direction. On the covers of both the blower motor and the Beckett, it has a picture of the cage with an arrow going CW from the furnace opening. Hope that helps. And, thank you! Your inquiry helped me! Thank you for your understanding of the units!
On 2016-12-09 by (mod) re: oil burner components & motor run direction must all agree
On most oil burners the 3 components are hooked up in this order, often from right to left:
Squirrel Cage fan
The motor couples to the fan that couples to the drive shaft of the fuel unit (fuel pump in your note)
They all spin in the same direction.
If a motor runs backwards (because of damage or mis-wiring) some components might also rotate but the system won't work at all.
In sum I agree with you. Besides anybody can simply LOOK into the oil burner assembly to see how things have to run.
On 2016-12-08 by Dan mcallister
On a Beckett burner if the fuel pump on the left side turns counter-clockwise and the blower on the right side with the squirrel cage turns doesn't that mean that that blower motor has two turn clockwise to make the oil pump turn counter-clockwise this was a big discussion and I was told I would have to turn counter-clockwise
I don't believe that is correct and the risk of sounding dumb can somebody tell me if I'm right or wrong I believe that if the oil pump is turning counterclockwise the blower motor has to turn clockwise
On 2016-12-05 by (mod) re: why does my motor run backwards after a power outage
You might want to review the article above for explanations of common causes of an electric motor running backwards. That's a good place to find things to check and repairs to try.
I suspect you'll find a bad start capacitor
On 2016-12-05 15:37:46.068835 by Grant
I had problems in the summer and replaced a small circuit board in the outside compressor and the unit seem to run fine in the cool mode. After I flipped it to heat mode although I had a little heat I noticed a lot of ice build up on the outside compressor coils.
Then we had a power outage yesterday and I noticed the fan running in reverse when the power came back on? The one thing I cant be sure of was it running in reverse when I changed the circuit board in the summer. suggestions please!
On 2016-11-09 by (mod) re: how to identify electric motor terminals to wire it correctly
To identify the specific terminals on your motor and thus the right wiring connections you need just the motor brand (Blaunecht) and model - see your motor's data tag. Then if you don't already have a wiring diagram for the motor I'd contact the company's tech-support:
Whirlpool UK Appliances Ltd
209 Purley Way
Tel: 0344 815 8989
On 2016-11-09 by (mod) re: how can I tell polarity of run and start windings on an electric motor
If your electric motor uses a starting capacitor to operate, you can reverse the starting direction of the motor by reversing the start winding polarity. It should be a simple circuit design to provide either a pair of start buttons or a cycling button that reverses the polarity on the start windings.
To reverse motor direction the motor will, of course, have to stop fully before re-starting in the opposite direction. Matthias Wandel, over at Woodgears.ca has written a nice, clear article on reversing electric motors of various phase and size designs. See https://woodgears.ca/motors/reversing.html
On 2016-11-09 by Bob W.
I have a Bauknecht single phase motor,start and run windings are not fastened to the switch, how can I tell the polarity of the start and run windings before fastening the wires to the switch.
On 2016-10-14 by Aditya mukati
How to turn a motor from left to right with button system
On 2016-08-12 by (mod) re: hydraulic fork lift motor runs backwards after I replaced the brushes
It's beyond my expertise so I won't try to say too much, but there are several reasons a motor runs the wrong direction, including the explanations I give in this article
http://inspectapedia.com/electric/Electric_Motor_Direction.php ELECTRIC MOTOR RUN DIRECTION - let me know if that helps you out. You can find that ariticle also (though I've given the link) by searching InspectApedia for "electric motor runs backwards"
On 2016-08-12 by Ron W.
I have an old Clark 24v forklift. Before I got it some one put new brushes in the hydraulic pump motor. NOW THE MOTOR RUNS IN THE REVERSE DIRECTION. I tried swapping the power leads but it still rotates the wrong way. Can you help me? Thank you.
On 2016-05-20 by edward
What is the standard direction of rotation of an electric motor. Also, what is the adequate size of generator to power a 15hp compressor motor.
On 2015-10-12 by Juan Flores Ojeda
Changer left from or to right motor industrial rotation !
Turned on our heat pump and system was working fine for about 3 hours. Without warning, the system started blowing heated air through the return. System had been off for about 2 weeks as we transitioned from summer to fall/winter. The filter on the system had just been changed. System is off now. What we thought was smoke was dust from the system. The air handler/return had been replaced about 5 years ago. Again, system seemed to be working fine. Any ideas? - A.S. 11/13/2013
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website. That said I offer these comments:
I'm guessing that in shifting from cooling to heating mode, your system correctly reversed refrigerant flow and began using the heat pump to heat building air, OR is running off of back up heat, perhaps electric, depending on outside temperatures. So the delivery of heat does not sound like it's part of the problem about which you ask.
Key in your statement is the rather unusual observation that air started blowing out of the return registers.
I suspect that you have a problem with the blower fan motor, wiring, or controls. It is possible for some electric motors to actually begin to run backwards. While a typical air handler blower fan uses a squirrel cage fan that does not move much air when it spins in the wrong direction, it will move some. And blowing air backwards through the return ducts might indeed be expected to dislodge dust, blowing it back into the occupied space.
Ask for service from your HVAC company, and see if the technician finds a bad electric motor winding, start capacitor, or electronic control, or possibly a control damaged by a power surge or outage.
We finally got resolution for our system. We had a bad capacitor replaced with the correct size. A few years ago, a capacitor went bad in the air handler and the technician replaced it; the issue (speculation) was that since he did not have the correct size on his truck, he used a smaller size that was minimal at best. It finally wore out. - A.S. 12/4/2013
Reply: Thanks so much ..., I'm glad it's resolved - I had not considered a too-small start capacitor installation as a source of later starting capacitor failure but it makes perfect sense.
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