Thermal relays are commonly used protection elements in electrical control systems to prevent motor overload. However, when a thermal relay trips, it can be due to the following reasons:
Thermal relay setting is too small: If the thermal relay setting is too small to accommodate the actual load current of the motor, it may cause tripping.
Motor load current is too large: When the motor load current is too large and exceeds the setting value of the thermal relay, the thermal relay will trigger trip protection.
Poor quality of thermal relays or poor contact contact: If the thermal relay itself is not of good quality, or if the contacts are not in good contact, it can also lead to tripping.
Poor quality of contactor or poor contact contact: Contactor is an important element in the control circuit, and if the contactor quality is not good or there is poor contact with contact, it may also lead to tripping.
After the thermal relay trips, a reset operation is required to restart the motor. There are two ways to reset the thermal relay: manual reset and automatic reset.
Manual reset: Manual reset can be achieved by pressing the reset button of the thermal relay. Manual reset should wait for 2 to 3 minutes before proceeding, as the internal curved hot plate needs to be cooled.
Automatic reset: When the thermal relay protection action, the normally closed contact is automatically closed, and the time of automatic reset is generally not more than 5min. The automatic reset can be selected by the reset adjustment screw, and the adjustment hole on the lower side of the thermal relay is extended with a slotted screw screw, and the reset adjustment screw (adjusted to the end) is tightened clockwise, which is the automatic reset mode; Loosen the reset adjustment screw counterclockwise so that the screw is unscrewed a certain distance and becomes a manual reset.
When using thermal relays, you need to pay attention to the following:
The thermal relay can only be used as the overload and phase failure protection of the motor, and cannot be used for short-circuit protection.
Selection of mounting points. The temperature difference between the installation place of the thermal relay and the installation place of the protected equipment should not be too large; There must be no vibration source at the installation point; When a thermal relay is attached to other electrical appliances, it should be installed underneath so that its operating characteristics are not affected by other heat-generating appliances.
The installation direction of the thermal relay should be the same as the direction specified in the product manual, and the deviation should not be greater than 5°.
The wiring screws of the thermal relay should be tightened, otherwise the contact resistance will increase and the temperature rise of the thermal element will increase, which will cause the thermal relay to malfunction.
The thermal relay of automatic reset should be adjusted to the automatic position, and it will automatically reset after 3 5min after the protection action; For the thermal relay that is manually reset, the reset button should be pressed after the protection action.
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In conclusion, understanding the cause of the tripping of a thermal relay and how to reset it is essential for the proper functioning of the electrical control system.
When using thermal relays, precautions should be taken for installation, use, and maintenance to ensure that they work properly and protect the equipment from damage.
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