Electrical checks on a Electric Motor

Here are some basic checks that can be done on a running motor when you take your rounds

1) Pressure Gauge

• Monitor suction and discharge pressure.

2) Ammeter Reading

• Check the current drawn while running.
• Pay special attention to the current during motor start-up.

3) Temperature and Vibration

• Touch and feel to check for abnormal heat or vibration levels.

4) Noise: Listen for abnormal sounds such as:

• Grinding
• Scraping
• Humming

5) Physical Condition

• Inspect for visible damage, corrosion, or water ingress.

Two important electrical tests that can be done on a Motor/equipment when the power is isolated or when overhauling the  motor are

1. Continuity test 
2. Insulation Resistance Test

Continuity Test

• Purpose: This test ensures that there is a complete and unbroken path for electrical current to flow through a circuit.It means there is a low resistance value between the points being tested, indicating a closed circuit
• Tools:  A continuity test can be performed with a multimeter
• Show a low resistance reading if the circuit is complete.

• Why is the Continuity test important?

• They help pinpoint the source of faults in circuits, allowing for faster and more accurate repairs.
• By detecting potential problems early, they help prevent larger issues and reduce downtime.
• They can test simple components like switches, fuses, and wires to ensure they are functioning correctly.

Insulation Test

• Purpose: This test measures the resistance of the insulating material around electrical conductors, like cables. It determines how well the insulation prevents current from leaking or flowing through the insulating material.
• Tools: An insulation test is carried out using a megger
• Usually done with a megger test with a test voltage of 500V DC for a 440V AC motor.

• Why is the Insulation test important?

• Crucial for ensuring the safety and reliability of electrical systems by verifying the integrity of insulation materials.
•  They help prevent electrical hazards like shocks, short circuits, and fires, as well as equipment downtime. 
• Regular insulation testing can also identify potential problems before they become major failures, allowing for timely maintenance and repairs.

Continuity test on a motor

Prove the equipment/motor is dead

• Set the Multimeter to Voltage Mode. Turn the dial to AC Voltage (V~ ~). Make sure it's set to a range higher than the system voltage (e.g., 600V range for a 440V system).
• To verify the Multimeter Works, test it on a known live circuit to make sure it reads voltage correctly.
• Open the motor terminal box.Using the multimeter probes, test:Phase-to-phase: (e.g., L1–L2, L2–L3, L1–L3)Phase-to-earth/ground: (e.g., L1–E, L2–E, L3–E)
• Expected result: 0 volts on all tests.

After proving the equipment/motor is dead using a multimeter

•  Turn the dial to the continuity setting
• If using a digital meter, you may hear a beep when continuity is detected.
• Test the Multimeter: Touch the two multimeter probes together.You should hear a beep or see 0 ohms (or very low resistance), indicating the meter is working.
• Access Motor Terminals,open the terminal box of the motor.Identify the motor winding terminals (typically marked U, V, W or T1, T2, T3).
• Test Winding Continuity touch the probe you want to test for continuity.
• You should get a low resistance reading (a few ohms), indicating good continuity

Insulation test- Using megger-tester

Usually done with a megger test with a test voltage of 500V DC for a 440V AC motor.

The test is performed by applying a current-limited DC test voltage between the conductors (e.g., Windings) and the Ground. Any current leakage is to be measured across the insulation’s dielectric materials. The current may be measured in milliamps or microamps and then calculated into Meg-ohms of resistance. The lower the current value, the greater the insulation resistance.

• The equipment/motor needs to be disconnected and locked out according to standard safety procedure
• Check megger function by shorting probes—pointer should indicate 0 MΩ.
• Prove the equipment/motor is dead using a multimeter or a megger tester. If using a megger test, connect the probes to a pair of conductors or motor terminals. If the pointer deflects, that means the circuit is live
• After ensuring the conductors are dead, it is safe to press the button and log the phase-to-phase insulation resistance. 3 readings should be measured U-V, V-W, W-U
• Then measure the phase to earth insulation resistance reading U-E, V-E, W-E
• The higher the resistance, the better the insulation.
• Results are typically in Meg-ohms (MΩ).