You may need to reverse a fan motor after a replacement, after rewiring, or when somebody reconnected the supply differently.
The method depends entirely on the motor type, and one type will not reverse at all.
On a three phase motor, swap any two supply leads. On a PSC motor, move the start winding connections as the wiring diagram shows. Shaded pole motors will not reverse at all. Many EC fans set direction by parameter or link. Never reverse a fan simply to flip airflow, since blades work in one direction only.
How to reverse a fan motor on three phase
This is easily the simplest case of the lot.
Swap any two of the three supply leads at the terminal block, and the rotating field flips. So the motor turns the other way with no internal changes at all.
Isolate and prove dead first, then label the leads before you disconnect anything. Meanwhile check the rotation arrow on the housing rather than guessing which way is correct.
Single phase capacitor motors
To reverse a fan motor of the PSC type, you change how the main and start windings relate.
- Isolate the supply and prove the circuit dead.
- Discharge the run capacitor through a suitable resistor.
- Find the motor wiring diagram, usually on the plate or inside the cover.
- Swap the two start winding leads as the diagram shows.
- Reinstate the capacitor connections exactly as drawn.
- Finally, confirm rotation before refitting any covers.
Some motors bring those leads out and some do not. Where the start winding stays buried, you cannot reverse the motor without opening it up.
Shaded pole motors cannot be reversed
The shading rings that create the rotating effect sit in fixed positions on the pole faces.
So the factory sets direction, and no wiring change alters it. If a shaded pole motor runs the wrong way, order one built for the other direction.
State rotation as viewed from a specific end, usually the shaft end, and confirm it against the fan housing arrow. Rotation described from opposite ends is a common source of wrong deliveries.
EC and DC fans
Electronic motors handle this differently, and often more conveniently.
- Many EC fans set direction by parameter or by a wiring link.
- Some models need configuration software or a service tool.
- DC fans may reverse with supply polarity, although only where the maker allows it.
- Never flip polarity on a fan whose datasheet stays silent about it.
- Check whether the datasheet derates performance in reverse.
- Finally, confirm the protection features still work the other way round.
Our EC wiring guide covers configuration, and our EC fan range lists which models support reversal.
The important warning about airflow
Reversing rotation does not give you a properly reversed fan.
Blades work in one direction only. Run them backwards and an axial fan gives roughly 40 to 60 percent of its rated airflow, noisily. Meanwhile a centrifugal wheel loses 50 to 70 percent and still draws real power.
So reversal fixes a wiring error rather than changing what the system does. Where you genuinely need reversible airflow, specify a fan built for it. Our rotation checking guide covers the diagnosis side, and it takes only a few minutes on site.
Confirming the result
Never assume the change worked, since a second mistake is easy to make.
Watch the wheel through the inlet guard with a torch, or feel which way the air leaves. On three phase, a phase rotation meter settles it outright. Meanwhile compare measured airflow against the curve when nobody can see the wheel.
For general motor connection practice, IEC 60034-8 covers terminal markings and direction of rotation.
Motor reversal FAQ
Can every fan motor be reversed?
No. Three phase and most PSC motors can, while shaded pole motors cannot. EC fans depend on the model and its configuration options.
Will reversing damage the fan?
Not usually in the short term, although bearings on some designs prefer one direction. So the real penalty is lost airflow rather than mechanical harm.
How do I know which direction is correct?
Check the arrow on the fan housing, then confirm which end it refers to. After that, verify by watching the wheel or by feeling the discharge.
Can I reverse an axial fan to exhaust instead of supply?
It will move air the other way at reduced performance and higher noise. For genuine reversible duty, specify a fan built with symmetrical blades.
Reverse a fan motor to correct a wiring error, never to change what the system does. Although the method takes minutes, the confirmation takes only seconds.
