Measure winding to winding on the plug feeding the motor (called phase to phase below). Resistances should be less than 20 ohms and nearly the same between all phases/windings. Measure from each winding to ground on the casing, and you should see no less than 100k ohms to ground.

Here are the methods used for the insulation of motor windings.

1. Dip and Bake. This is among the most common insulation methods used for motor windings.
2. Trickle Varnishing. In this method, the windings will be connected to electrical wires on a rotating table.
3. Vacuum Pressure Impregnation.
4. Ultra-Seal Winding.

You should test the windings for a “short to ground” in the circuit and open or shorts in the windings. To test your motor for short to ground, you’ll need to set the multimeter to ohms and disconnect the motor from its power source. Then inspect each wire and look for infinite readings.

Diagnosing ECM Motors

1. Verify that the correct thermostat input voltage is present at the interface of the main control board on the furnace or air handler.
2. When checking low-voltage connections, always use the C terminal on the board, never on the ground.

Running a three phase motor on single phase power is simple. Essentially all you need to do is wire the single phase power to the input side of your variable frequency drive and then wire the three phase power of your motor to the output section of the drive. That’s it!

Comparing single-phase vs. three-phase power, three-phase power supplies are more efficient. A three-phase power supply can transmit three times as much power as a single-phase power supply, while only needing one additional wire (that is, three wires instead of two).

If you require a motor for use in industrial, commercial or professional sectors, the three-phase motor is the better choice – it is more efficient, offers more power and is good value for money, regardless of the higher costs.