Control wires for a thermal overload relay are connected through the relay's auxiliary contacts to the motor control circuit, ensuring the motor shuts down during overload or overheating conditions.

Step-by-Step Connection Guide

1. Safety First Before starting, ensure the motor and power supply are completely de-energized. Use lock-out/tag-out procedures to prevent accidental re-energization, as improper handling can cause electrical hazards . 2. Identify Relay Terminals A typical thermal overload relay has:

• Main terminals (L1, L2, L3) for the motor power supply
• Motor terminals (T1, T2, T3) for motor connection
• Auxiliary contacts (NC and NO) for control circuit integration 3. Power Circuit Wiring
• Connect the incoming power supply to the relay's input terminals (L1, L2, L3).
• Connect the motor leads to the relay's output terminals (T1, T2, T3).
• This series connection ensures the relay senses the motor current and trips if it exceeds the set value . 4. Control Circuit Wiring
• Use the normally closed (NC) auxiliary contact to break the control circuit when the relay trips. This contact is typically wired in series with the motor starter coil or control switch.
• The normally open (NO) contact can be used for signaling, such as activating an alarm or indicator light when the relay trips .
• Ensure all control wires are properly insulated and securely connected to prevent loose contacts or short circuits. 5. Setting the Trip Current
• Adjust the relay's trip setting according to the motor's full-load current. This ensures the relay activates only during genuine overload conditions . 6. Testing and Reset
• After wiring, test the system by simulating an overload condition or using the relay's test function.
• Reset the relay using the manual or automatic reset button after a trip to restore normal operation .

Additional Tips

• Always follow the manufacturer's wiring diagram for your specific relay model.
• For self-holding (latching) relays, ensure the control wiring allows the relay to maintain its tripped state until manually reset .
• Verify that the relay's current rating matches the motor's specifications to prevent nuisance tripping or insufficient protection. By following these steps, the thermal overload relay will effectively protect the motor from overheating, phase imbalance, and prolonged overcurrent, while the control wiring ensures safe and reliable operation of the motor control circuit .