Contactor working principle is: after the contactor coil current, coil current creates a magnetic field, the magnetic field generated electromagnetic suction attract moving iron core, makes the static iron core and lead point of ac contactor, normally closed contacts disconnect, normally open contact closure, the two are linked. Disappear when coil power, electromagnetic suction, armature in released under the action of the spring, make contact recovery, normally open contacts disconnect, normally closed contact closure. The working principle of dc contactor is similar with the principle of temperature switch.