External thermal relay operation

What does E.OHT mean?

This fault signifies that an external thermal relay (for motor overheat protection) or an internal motor temperature relay has tripped, causing its contacts to open. The inverter has stopped its output to protect the motor from overheating. This function is active only when the 'OH' signal (value 7) is set in any of Pr. 178 to Pr. 182 (input terminal function selection). Prolonged motor overheating can lead to winding insulation breakdown and motor failure.

• Motor overloading for an extended period, leading to winding temperature rise above safe limits.
• Inadequate motor cooling due to blocked ventilation fins, failed cooling fan, or high ambient temperature.
• External thermal relay set point (e.g., Pr. 60) too low for the application or incorrect motor thermal model selected.
• Loss of one motor phase (single-phasing) causing other phases to draw excessive current and overheat.
• Faulty external thermal relay or wiring (e.g., open circuit) providing a false trip signal to the inverter input (e.g., terminal T1).

Click steps to track your progress.

1. 1

   Disconnect main power supply to the inverter and wait for DC bus discharge (measure terminal V+/V- for 0VDC).

2. 2

   Manually reset the external thermal overload relay and verify its contact status (e.g., 95-96 terminals should be closed).

3. 3

   Measure the resistance across the external thermal relay's normally closed (NC) contacts, confirming continuity (should be < 1 ohm).

4. 4

   Inspect the motor for blocked cooling fins, debris accumulation, or non-functional integrated cooling fan.

5. 5

   Verify motor load percentage (e.g., Pr. 02) during operation to ensure it is within the motor's rated capacity for extended periods.

6. 6

   Check the motor nameplate rated current and compare it to the thermal relay trip current setting (e.g., Pr. 60 or relay dial setting).