Troubleshooting a Dual Voltage 3-Phase Motor

Our subject matter experts (SME) at Multi-Skill Training Services have found the most efficient way to troubleshoot a dual voltage 3-phase motor for winding failure.  Time and accuracy are two important factors with troubleshooting, and this begins with checking that the motor and drive system is receiving the high quality power it needs and is not adversely affecting power quality upstream.

  • Preparation:

1) Make sure all power has been isolated from the motor
2) Make sure the motor is wired for high voltage; this puts the coils in series with each other.

  • Resistance to ground should be very HIGH or OPEN

1) Check resistance from Lead 1 to ground.
2) Check resistance from Lead 2 to ground.
3) Check resistance from Lead 3 to ground.

If resistance is low (under 100 ohms) or one lead has much less resistance to ground than other leads, then the motor has a short to ground.

  • Resistance Lead to Lead should be the same for each pair of motor leads.

1) Check resistance from Lead 1 to Lead 2.
2) Check resistance from Lead 2 to Lead 3.
3) Check resistance from Lead 1 to Lead 3.

If the matter reads OL on a pair of leads, then that coil is OPEN.

If the meter reads less resistance on a pair of leads than other pairs, then that coil is SHORTED. 

IF ALL PAIRS OF LEADS READ THE SAME AND THE MOTOR IS NOT SHORTED TO GROUND, THEN THAT MOTOR IS MOST LIKELY GOOD. 

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