Relays rely on an electromagnet, which pulls the switch mechanism, or lever, moving it to the on or off position based on the level of electromagnetic energy received. Relays control circuits with a low-power signal, and via the switching mechanism, enable a high-energy current to flow through those circuits.
Solid State Relays
Solid-state relays control large-load currents through a small control signal. A current sensor responds to the control signal, which is used to switch the power on or off. A solid-state relay operates similarly to electromechanical relays, but contains no moving parts. Solid-state relays are often used with machinery that requires high levels of voltage.
Protective relays calculate the operating conditions of electrical circuits, and are used to interrupt, or trip, circuit breakers when a fault is detected. A fault is an unintended electrical connection, or “short circuit.” Protective relays are used to protect electrical equipment from such harmful conditions as over-voltage, over-current or reverse-power flow.