CSLB C-20 HVAC ContractorControls, Electrical and SafetyMedium
A technician wires a new three-phase condenser fan motor and, upon startup, observes the fan blade spinning in the wrong direction, reducing airflow across the coil. What is the correct corrective action?
- AReverse the motor's run and start capacitor connections
- BSwap any two of the three incoming line leads at the motor terminals
- CReplace the motor with a single-phase equivalent
- DIncrease the motor's overload trip setting to compensate
Show answer & explanationAnswer & explanation
Correct answer: B. Swap any two of the three incoming line leads at the motor terminals
Three-phase motor rotation direction is determined by phase sequence; swapping any two of the three line leads reverses the rotating magnetic field and corrects the direction of rotation. Capacitors are not used in standard three-phase motors, and overload settings have no effect on rotation direction.
Why the other options are wrong
- A. Three-phase motors typically do not use start/run capacitors; this applies to single-phase motors.
- C. Replacing with a single-phase motor is unnecessary and not a proper corrective action for wiring error.
- D. Overload settings protect against overcurrent and have no bearing on rotation direction.
Three-Phase Motor Rotation Reversal
The direction of rotation of a three-phase motor is determined by phase sequence; swapping any two of the three line leads reverses rotation direction.
- Three-phase motors have no capacitors for starting
- Rotation depends on phase sequence (e.g., L1-L2-L3 vs L1-L3-L2)
- Swap only two leads—swapping all three has no effect
Memory trick: Swap two, spin true.