A magnetic relay is an electromagnetic switching device that uses the magnetic force generated by an electric current to control the on/off state of another circuit. It acts as an "electric switch" with isolation between the control circuit and the controlled circuit, ensuring safety and enabling the control of high-power or high-voltage circuits using low-power signals. Widely used in industrial control, household appliances, and automotive electronics, magnetic relays are valued for their reliability, long lifespan (typically 100,000-1,000,000 operations), and strong anti-interference ability.

The core structure of a magnetic relay consists of four parts: electromagnetic system, contact system, return mechanism, and insulation housing. The electromagnetic system includes an iron core, a coil, and an armature—when an electric current passes through the coil, the iron core is magnetized to generate a magnetic field, attracting the armature to move. The contact system is composed of moving contacts and static contacts: the armature movement drives the moving contacts to touch or separate from the static contacts, thereby controlling the on/off of the controlled circuit. The return mechanism (usually a spring) pulls the armature back to its original position when the coil is de-energized, resetting the contacts. The insulation housing isolates the electromagnetic system from the contact system, preventing electrical leakage and ensuring safe operation.

Magnetic relays are classified based on their functions and structures. For example, DC relays use DC current in the control coil and are suitable for low-voltage DC circuits (e.g., 12V automotive control circuits); AC relays use AC current and are commonly used in household appliance control (e.g., air conditioner compressors). According to the number of contacts, they can be divided into single-pole single-throw (SPST), single-pole double-throw (SPDT), and multi-pole multi-throw (MPMT) relays—SPDT relays are widely used in circuit switching scenarios (e.g., changing the direction of a DC motor).

In practical applications, magnetic relays play a key role in safety protection and automatic control. For instance, in a household washing machine, a magnetic relay controls the power supply of the motor: when the user selects a washing program, the control circuit sends a low-power signal to energize the relay coil, closing the motor circuit to start the washing process; when an overload or water leakage occurs, the control circuit cuts off the coil current, the relay contacts disconnect, and the motor stops immediately to avoid damage. In industrial automation, magnetic relays are used to control high-power equipment such as motors and heaters, enabling remote control and centralized management of production lines.