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    The common faults of motor overload protection device are as follows:

    Thermal relay fault

    –  Misoperation  : The ambient temperature is too high, which makes the bimetal sheet of the thermal relay act in advance, resulting in cutting off the circuit when the motor is not really overloaded. Or the motor starting time is too long, the starting current is large and the duration is long, which will also cause the thermal relay to misjudge the operation as overload.

    –  No action  : The setting value of the thermal relay is too large, that is, the overload protection current value set is much higher than the actual overload current of the motor, resulting in the thermal relay cannot act in time when the motor is overloaded. Or the bimetal sheet aging after long-term use, the action characteristics change, and the normal bending can not push the contact action when overloaded.

    The fuse is faulty

    –  Misfuse  : The melt selection of the fuse is too small, and it will fuse under the normal short-time large current impact such as motor startup. Or the melt installation is subject to mechanical damage, so that its cross-sectional area becomes smaller, the resistance increases, and it may also be fused due to overheating under normal current.

    –  No fusing  : The rated current of the melt is too large, and when the motor fails such as overload or short circuit, the current cannot reach the fusing current of the melt, resulting in the fuse not fusing in time to cut off the circuit. In addition, the contact of the fuse is poor, so that the contact resistance increases, the heat is mainly concentrated at the contact, and the melt can not reach the fuse temperature, there will be no fuse.

    Electronic overload protector is faulty

    –  False alarm  : Electronic components are subject to electromagnetic interference, resulting in a deviation in the current detection signal, so that the protector is misjudged as overload and alarm. Or the parameter setting is unreasonable, such as the overload operation time is set too short, the current threshold is set too low, may lead to false alarm during the normal operation of the motor.

    –  Inaccurate detection  : The current transformer is faulty, and the current in the main circuit cannot be accurately converted into a small current signal in proportion to the input to the electronic circuit, so that the electronic overload protector cannot accurately detect the motor current. Or the filter, amplification and other components in the electronic circuit are damaged, which will also cause the detected current signal to be inaccurate, affecting the normal function of overload protection.

    Other common faults

    –  Wiring failure  : Loose wiring will cause the contact resistance to increase, so that the current detected by the protection device is not accurate, may also produce local overheating, affecting the normal operation of the protection device, and even cause failure. If the wiring is incorrect, for example, the inlet and outlet of the protection device are reversed, the protection device cannot detect the current or voltage normally, resulting in the failure of the protection function.

    –  Power failure  : The power supply voltage is too low, which will make the thermal relay and electronic overload protector work unstable, and there may be misoperation or no action. Excessive voltage fluctuation of the power supply will cause damage to the electronic overload protector and affect its normal operation. For a three-phase power supply, the three-phase voltage imbalance will cause the current detected by the protection device to be unbalanced, which may trigger a false alarm or affect the protection effect.