Thermal relay is a simple and reliable motor overload protection. But it only works if configured correctly. Incorrectthermal protectionsetting either does not save the engine or interferes with operation due to false shutdowns. Let's figure out how to set it up correctly.
How a thermal relay works
The relay monitors the motor current and, if it is exceeded for a long time, turns it off, simulating the thermal inertia of the winding. This protects against overload, phase loss and jamming.
How to select the setting
The thermal relay setting is set according to the rated motor current indicated on the nameplate:
- Find the rated current on the motor nameplate.
- Set the relay setting equal to this current (usually the relay range is selected so that the rating is in middle).
- Take into account the connection diagram - when starting star-delta, the calculation is different.
| Situation | Action |
|---|---|
| Frequent false shutdowns | Check whether the setting is too low |
| The engine is heating up, the relay is not working triggered | The setting is too high - reduce it |
Typical errors
- Setting the set point “by eye” without taking into account the nominal value.
- Increasing the set value to get rid of shutdowns - this deprives the motor of protection.
- Using only a thermal relay without protection against phase loss.
Thermal relay does not replace full-fledged accident protection - for critical equipment, phase control relays are additionally installed. If the motor has already suffered from overload, rewind will be required.
Do you need help with engine protection at an enterprise in Tashkent? Elektromotors engineers will select and configure protection - contact us.