External Thermal Relay Operation

What does External thermal relay operation mean?

The external thermal relay connected to the OH signal has been activated. This indicates that the motor or connected equipment is experiencing an overload condition, potentially causing damage if not addressed. The inverter will not restart unless it is manually reset after the relay contacts return to normal.

• Motor overload due to increased mechanical load beyond its rated capacity.
• Motor cooling fan failure or blocked ventilation, leading to motor overheating.
• Incorrect sizing of the external thermal overload relay; trip current set too low.
• Faulty wiring or loose connection between the external thermal relay's NC (Normally Closed) contact and the inverter's OH input terminal.
• External thermal relay itself is defective, tripping prematurely without actual overload.

Click steps to track your progress.

1. 1

   Measure motor winding temperature directly using an infrared thermometer to confirm actual overheating.

2. 2

   Check the mechanical load on the motor for any binding, blockage, or unusual resistance.

3. 3

   Verify the external thermal relay's trip current setting matches or slightly exceeds the motor's FLC (Full Load Current).

4. 4

   Inspect the wiring from the thermal relay's NC contact to the inverter's OH terminal for continuity and secure connections.

5. 5

   Bypass the external thermal relay for a short diagnostic test (ensure system safety, monitor motor temperature closely) to isolate relay fault.

6. 6

   Measure motor current during operation using a clamp meter and compare to motor nameplate FLC (Full Load Current).