At the core of an electromagnetic relay lies the interaction between electric current and magnetism. The device typically consists of four main components: the coil, an iron core, a set of contacts, and a spring. When an electrical current passes through the coil, it creates a magnetic field that attracts the iron core. This action causes the moving contacts to either close or open, depending on whether they are normally open (NO) or normally closed (NC) contacts.

    When the coil is energized, the magnetic field is strong enough to pull the core, moving the contact arm and altering the state of the contacts. For a NO contact, this results in the connection being made, allowing current to flow through the circuit. Conversely, for NC contacts, the relay will break the circuit when energized. Once the current to the coil is turned off, the magnetic field collapses, and the spring mechanism returns the contacts to their original state.