Peel magnetic relays – how thermal relays control contactors

Create Date: 2024-8-30 12:03:23|Source: PILZ/PILZ

The main function of a thermal relay is to protect the motor.

The new electronic thermal relay has protection against overload, overcurrent, blocked rotor and various phase faults, current unbalance, interphase short circuit, inter-turn short circuit or overvoltage, undervoltage and so on.

We should pay attention to the following points in the process of using thermal relays.

First, when the motor starts for too long or the number of operations is too frequent, the thermal relay will malfunction or burn out the electrical appliance, so in this case, the thermal relay is generally not used for overload protection.

Second, the connecting wire at the outlet end of the thermal relay should be selected appropriately, if the wire is too thin, it will affect the relay may act in advance, if the wire is too thick, the thermal relay may lag in action.

Thirdly, when the thermal relay is installed together with other electrical appliances, it should be installed under other electrical appliances to avoid the influence of other electric heating on its working characteristics.

Fourth, the rated current of the thermal relay should be greater than the rated current of the motor.

Fifth, generally light load start, short time work, you can choose a two-phase structure of thermal relay, when the balance of the power supply voltage and the working environment is poor or the power difference of multiple motors is more significant, you can choose a three-phase structure of thermal relay.

Sixth, the normally closed point of the thermal relay is generally used to control the power supply of the contactor coil, and the normally open point of the thermal relay is used as the fault signal for power supply.

Seventh, generally adjust the setting current to be equal to the rated current of the motor, for the motor with poor overload capacity, the setting value of the thermal relay can be adjusted to 0.6 to 0.8 times the rated current of the motor, for the motor with a long starting time, dragging impact load or not allowed to stop, the setting current of the thermal relay should be adjusted to 1.1 to 1.15 times of the rated current of the motor.

Peel magnetic relays – how thermal relays control contactors

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