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5 Crucial Electric Motor Inspection Tests You Should Know

5 Crucial Electric Motor Inspection Tests You Should Know

Maintaining every little detail is essential when it comes to preventive maintenance of your electric motor. As the classic adage goes, “an ounce of prevention is worth a pound of cure!” Hence, an effective preventive maintenance procedure on your electric motor requires a thorough inspection.

Inspection is a crucial step that you need to take to properly diagnose and prevent any possible breakdown or damage to your electric motor that could sometimes lead to electric motor rewinds or overhauling. Inspection testing of an electric motor is an integral part of establishing your equipment’s condition and the troubleshooting process’s start.

Read on to find out some of the most common and significant inspection tests you can perform to ensure your electric motor runs efficiently.

1. IR to Ground Test

An IR to Ground Test is an instrumental electric motor inspection test, as it examines anomalies that are sure indicators of a motor that will fail or have failed already. This test is usually conducted on three phase motors wherein the inspector measures the insulation resistance (IR) between the motor frame and each motor windings. Hence, it requires an IR tester that can read the expected high levels of resistance.

When conducting an IR to Ground Test, it is necessary to note a link between resistance and temperature. As the temperature alters, the resistance also changes. For the values of the IR to be significant, they should be determined with a reference temperature for the winding, and the IR values should be corrected to correspond to the standard 40° Celsius reference temperature.

2. Polarisation Index Test

The Polarisation Index Test is an IR to Ground Test conducted over 10 minutes. It delivers valuable information about the condition of the motor insulation with respect to cleanliness and moisture. Once data has been obtained, the value at the 10-minute mark is divided by the value at the 1-minute mark to come up with a ratio that is significant as it traced

overtime for a motor.

3. Surge Comparison Test

Electric motors usually undergo both final and incoming Surge Comparison Tests. Most of the time, a Surge Comparison Test requires the use of a multi-functional surge tester to be performed effectively. The primary purpose of this test is to discover insulation shorts and weaknesses and detect improper internal connections or erroneous turn counts.

4. Winding Phase-to-Phase Resistance Test

Winding Phase-to-Phase Resistance Tests are typically performed to detect any huge differences in resistance between the windings. This test is a standard repair test for AC motors. For an electric motor to be considered well-running, the resistance of each winding must be the same. A standard low resistance ohmmeter is often required for this type of test.

5. DC Voltage Drop Test

If the Winding Phase-to-Phase Resistance Test is for AC motors, then the DC Voltage Drop Test is for DC motors. This test is specifically for the repair of DC motors and is the primary testing method for determining shorted turns in a DC motor’s field windings, interpoles, series, and shunts. It is conducted by having voltage applied to the interpoles and shunt fields, and then the voltage drop between the same feeds will be measured. Take note that both DC and AC voltages are applicable in this test.


Inspection is undoubtedly an integral part of an electric motor’s preventive maintenance. By implementing a rigorous electric motor inspection testing regimen, you can save plenty of dollars to avoid delays and downtime due to motor failure. To help make sure your electric motor is always in good shape, it is highly recommended that you partner with a reliable mechanical and electrical engineering company in Singapore when it comes to maintaining your equipment.