Did You Know – Phasing Revised

When it comes to installing 3 phase HVAC equipment confirming proper voltage and rotation is vitally important.

When It Comes To Three Phase Equipment Did You Know:

  • Three phase power distribution requires smaller conductors for transferring the same amount of power as compared to single phase power.
  • All York 3phase equipment is phased for clockwise rotation.
  • Changing the direction of rotation of the motor is as simple as swapping any two wires.
  • Three Phase motors last longer than single phase motors.
  • Three Phase motors are available in a much larger range of horsepower sizes.
  • Three phase motors less parts. No capacitors are required on 3phase motors.
  • 60 (Hertz) means that 60 times per second each phase of power makes one peak and valley (a full circle).

Important Notes:

Phasing can typically be tested by quickly pressing in on the load contactor (bumping). Equipment could be damaged by improper phasing. Observing the blower motor to check for proper rotation can a good visual test, the caveat to this is that when motors use a variable frequency drive (VFD) the phase rotation will be automatically corrected internal to the VFD making this an unreliable test in the case where a VFD is used.  Also keep in mind that most condenser fan motors are single phase therefore using these motors to confirm phasing is also unreliable.

It’s important that each of the three Legs/Lines of power all offer the same voltage, without variance.  This is best tested while the system is running at peak power draw. A voltage imbalance will cause increased winding heat which leads to premature failure. To test for three-phase imbalance always check from phase to phase not from phase to ground.  Check voltage from each of the three phases to one another and find the average (add all three then divide by three), then divide the leg that is farthest from average voltage by average voltage.  You will want to make SURE the imbalance is below 2%.  If voltage imbalance exceeds this you will want to inspect the power supply for the following; melted wires, loose terminals and lugs, undersized wire, pitted contacts, poor disconnect fuse contact etc…

Thank you for your time!

Will Grauberger
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