Thermal overload relay adjusted to the motor's rated current. (For service factor motors, approximately SF × I_n). A relay is selected that averages this value for the adjustment range; the tripping class (Class 10/20/30) is determined according to the load's starting time.
Setting ≈ SF × I_n (IEC/EN 60947)
Example calculation: For a motor with a rated current of 28 A, the SF 1.0 → thermal relay is set to ≈ 28 A (a relay with an adjustment range of ~23–32 A is selected).
Thermal (Overload) Relay Setting
Find the recommended setting value for the thermal overload relay based on the motor's full load current.
Suggested setting
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Relay range (recommendation)
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Notes: The overload relay is set to the motor's rated current (approximately SF×I_n for motors with a service factor); within the scope of IEC/EN 60947, a relay is selected whose setting range averages this value. Opening class (Class 10 / 20 / 30) It is determined according to the departure time of the cargo.
How is it calculated?
- Enter the motor full load current (I_n).
- Enter the service factor (SF).
- Press Calculate.
Frequently Asked Questions
What setting should the thermal relay be set to?
The current is adjusted to the motor's rated (full load) current; for motors with a service factor, it is approximately SF × I_n.
What is the opening class (Class 10/20)?
This class specifies the overload tripping time of the relay; a higher class is selected for loads with longer tripping times.
How to choose a relay?
A relay is selected whose adjustment range averages the motor's rated current.
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