Possible Cause                    


Recommended Action

Fan running the wrong way Incorrect wiring.  

To reverse the rotation of a three-phase motor interchange any two supply leads.  To reverse the rotation of a single-phase motor interchange leads on the start winding.  Refer to the directions in the motor junction box.

This note applies to single-speed motors only.  For 2-speed motors refer to the supplier.

Fan won't run Wrong electrical supply.   Check the electrical supply matches the motor nameplate.
  Electrical connections in the motor terminal box or starter are not tight.   Check and tighten as necessary.
  For single-phase motors the capacitor is not wired in or is faulty.   If a capacitor is fitted check with a multimeter or replace.
  Fuses are blown.   Before replacing fuses check the motor circuit for any faults.
  Belts on belt-driven units have broken.   Replace the belts and re-align the drive.
  Overloads have tripped out.   Check the motor before resetting the overloads.
  If a variable speed drive (VSD) has been fitted incorrect installation can cause an electrical 'spike' causing the motor windings to fail.   Check the motor windings and if failed replace the motor. Check the installation is in accordance with the VSD supplier's recommendations.
Fan runs in alternate direction. The capacitor is not in circuit or it could be faulty.   Check with multimeter or replace.
  Alternatively, the connections could be poor or incorrect.   Check all connections and ensure there are no loose terminals.
Electrical hum Electronic speed-controllers can generate an electrical hum.   If the electronic controller is not faulty explore using a SSC single-phase 2-speed switch in its place.  Alternatively, use an auto-transformer speed controller.
  If a variable speed drive (VSD) is fitted incorrectly it can cause a high level of harmonics in the supply.   Check the installation conforms to the VSD supplier's recommendations.
  Phase imbalance on three-phase motor.   Check and correct the supply.
  Motor is not designed for the electric supply ie. wrong voltage or frequency.   Check the electrical supply matches the motor nameplate.
  Motor is overloaded and drawing greater than the nameplate amps.   Check the correct motor is fitted.  If correct check the pitch-angle if an axial fan or the belt-drive details if a belt-driven fan.  If these are correct contact the supplier.
  Motor has excessive clearance between stator and rotor.  In this situation the motor will run slower than the normal speed. ie.  have excessive slip.   Check motor speed, if slow contact the supplier.
Motor overheating or high current draw. Faulty instruments.   Ensure all instruments are accurate and calibrated where necessary.
  Incorrect power supply.   Check the electrical supply matches the motor nameplate.
  Three-phase motor running with one phase disconnected.  This is called single-phasing.  When single-phasing, the motor will draw uneven current on each phase and will generally not start from standstill.   If single-phasing, check if it is the power supply or the motor windings.  If a winding has failed the motor may need to be replaced.  Fitting correct overloads or phase protection will prevent this problem.
  Impeller has too much inertia for the motor power and does not achieve full speed.   Check the inertia of the load and reduce as necessary.  Alternatively, fit a larger motor.
  Excessive dirt on the motor cooling fins so the heat is not able to dissipate.   Remove the dirt and dust on the motor body and between the cooling fins.  Increase the maintenance frequency.
  If the motor is out of the air stream either the cooling fan is not fitted or the air inlet to the motor cooling fan is obstructed.   Fit the motor cooling fan if not fitted and remove any obstructions from the air inlet to the motor.
  Excessive stopping or starting - 10 starts/hour is generally acceptable.   Check the control system and reduce the number of starts/hour as recommended.
  A conventional three-phase motor is connected in Delta when it should be in Star, or vice-versa.   Check the motor nameplate and re-wire correctly.
  The fan impeller is jammed resulting in a locked rotor situation.  The motor will draw 6-10 times the rated current in this situation.   Check to ensure the impeller can rotate freely.
  A 2-speed motor, when switching from high to low speed, can generate heat if the supply is not switched off.   Switch off the power first and allow the motor to run down before engaging low speed.  Alternatively, use a time delay interlock.
  Backward-curved centrifugal impellers may be running in the wrong direction.  When running in the wrong direction they will tend to overload the motor.  Airflow capacity will be down to approximately 30-40% of full flow.   Check and correct the direction of rotation of the impeller if necessary.
Motor overheating or high current draw. If the fan is a forward-curved centrifugal there may be insufficient system resistance.   Ensure the duct system is installed correctly and, if necessary, lower the fan speed.  Alternatively, increase the system resistance by fitting perforated metal on the fan inlet but note that this is inefficient.
  Axial fan impeller over pitched.   Re-pitch to the correct angle.
  Error in the motor selection for the required duty.   Check the motor nameplate and change as necessary.
  With belt-drive units incorrect pulley selection or pulleys on the wrong shafts.   Check the pulley ratio and that the pulleys are on the correct shafts.
  Gas density greater that design.    Increase the motor size to suit.