There are two pairs of normally open and normally closed because two groups must be used, and the most common one is a group of normally open and normally closed.

First we master the working principle of AC contactor.

When the AC contactor coil is connected to the power supply, the coil current will cause the electromagnetic field. The electromagnetic field will cause the static transformer iron core to cause the electromagnetic induction adsorption force, which will move the transformer iron core and push the AC contactor to the point position. The normally closed contact will break and the normally open contact will close.

When the coil turns off the power supply, the electromagnetic induction adsorption force subsides, and the streamline coil is released under the effect of springing yellow, so that the contact point is restored, and the normally open contact is broken. In fact, the key principle of normally closed contact is the magnetic effect principle of current. After the power supply is connected, there is magnetic, so the posture of the magnet promotes the work of the AC contactor.

When will there be two groups of normally open and normally closed? When one group is insufficient, we must improve it. For example, for the more complicated control circuit, one group can only complete one function, and when the function is completed, we must improve another group.