How to Test a Motor with a Multimeter

Identify your test equipment

Confirm that your digital multimeter is functioning correctly and set aside the tools you will need for the procedure. Along with the multimeter, keep pliers, screwdrivers, and a clamp meter within reach for accessing and testing the terminal box.

Review the tests you will perform

With a multimeter, you can perform four checks on an induction motor:

• Continuity test: Confirms that each winding's coil connections (U1-U2, V1-V2, W1-W2) are intact.
• Short circuit test: Confirms that the windings are not shorted to one another.
• Ground leakage test: Confirms that no winding is making contact with the motor body.
• Resistance test: Compares resistance values between windings to check for uniformity.

Locate and identify the motor terminals

Open the terminal box and locate the six leads. These are typically labeled U1, U2, V1, V2, W1, and W2, and may also be color-coded. Correct identification of each terminal is essential before you begin testing.

Reference the winding diagram

Use the winding diagram to confirm which terminal pairs belong to the same winding: U1-U2, V1-V2, and W1-W2. This diagram guides both the continuity and resistance tests that follow.

Match terminal pairs before testing

Note that matching terminal numbers (for example, U1 with U2) indicate the two ends of the same winding. Wire color can help confirm pairs, but be aware that all wires may sometimes appear the same color. If colors are not distinct, rely on the multimeter readings instead of color alone to identify winding pairs.

Prepare the multimeter for continuity testing

Safety note: Confirm the motor remains disconnected from any power source before proceeding. Set your digital multimeter to continuity mode, typically indicated by a sound wave or diode symbol, and keep the probes within easy reach of the terminal box.

Test continuity between each winding pair

Place one probe on U1 and the other on U2, then listen for a beep or observe a low resistance reading to confirm continuity. Repeat this process for V1-V2 and then W1-W2. Each pair should register continuity, confirming the winding is intact.

Record the resistance value for each pair

As you test each pair, note the resistance value shown on the multimeter display. Healthy windings typically show low, similar resistance values across all three pairs. Example readings from this procedure were:

• U1-U2: 0.30 Ω
• V1-V2: 0.29 Ω
• W1-W2: 0.22 Ω

Consistent readings across all pairs indicate the windings are likely in good condition.

Verification: Confirm that all three winding pairs show continuity and similar resistance values. If any pair shows no continuity or a very high resistance reading, that winding may be open or damaged. If resistance values differ significantly between pairs, investigate further before proceeding.

Test for short circuits between windings

With the multimeter still in continuity mode, place one probe on U1 and the other on V1, then repeat for U1-W1 and V1-W1. These cross-winding tests should show no continuity — either no beep or an infinite resistance ("OL") reading. If you detect continuity between different windings (for example, U1 and V2), this indicates a short circuit, which must not be present. Only matching pairs (U1-U2, V1-V2, W1-W2) should ever show continuity.

Test for ground leakage

Place one multimeter probe on a winding terminal (for example, U1) and the other probe on a bare metal part of the motor body. Repeat this test for all six terminals. There should be no continuity — no beep and an infinite resistance ("OL") reading — between any terminal and the motor body. Any reading indicates ground leakage, which may result from damaged insulation or a cut wire touching the stator, and confirms the windings are not properly insulated from the motor frame.

Safety note: If you get a resistance reading or a beep during this test, there is a ground fault. Do not use the motor until the fault is repaired.

Confirm the motor body is conductive

Before finalizing your ground leakage results, verify that the multimeter correctly detects the motor body as conductive. Touch a probe to a bare metal part of the motor body while confirming the meter's response, ensuring your test setup is valid.

Test each remaining terminal against the motor body

Place one probe on the motor body and the other on each terminal in turn — U1, V1, W1, and any remaining leads. The display should show "OL" or infinite resistance for each terminal, confirming no ground leakage.

Confirm the motor is ready for use

Once continuity, short circuit, and ground leakage tests have all passed, the motor is confirmed healthy and ready for operation.

Complete all checks before powering the motor

Safety note: Double-check that continuity, short circuit, and ground leakage tests have all been performed and passed. Only connect the motor to a power source after confirming all results are satisfactory.