Electromagnetic relay is generally composed of iron core, coil, armature, contact reed and so on.

As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, thereby generating an electromagnetic effect. The moving contact and the static contact (normally open contact) are sucked together.

When the coil is powered off, the electromagnetic attraction will also disappear, and the armature will return to its original position under the reaction force of the spring, so that the moving contact and the original static contact (normally closed contact) will be released. In this way, it is attracted and released, so as to achieve the purpose of conducting and cutting off in the circuit.

For the "normally open and normally closed" contacts of the Electromagnetic relay, it can be distinguished in this way: the static contact in the off state when the relay coil is not energized is called the "normally open contact"; the static contact in the on state Called a "normally closed contact".