Electromechanical relays are devices that complete or interrupt a circuit by physically moving electrical contacts into contact with each other. A relay involves two circuits: the energizing circuit and the contact circuit. The coil is on the energizing side and the relay contacts are on the contact side. When a relay coil is energized, current flow through the coil creates a magnetic field. Whether in a DC unit, where the polarity is fixed, or in an AC unit where the polarity changes 120 times per second, the basic function remains the same: the magnetic coil attracts a ferrous plate, which is part of the armature. One end of the armature is attached to the metal frame that is formed so that the armature can pivot, while the other end opens and closes the contacts. Relay contacts are designed, built and specified for the type of application for the relay. No single voltage and current rating applies to a given set of contacts under all circumstances. Contact the relay manufacturer for guidance if your requirements are unusual or the specifications seem incomplete.