Undervoltage Relay

Electromechanical Relays
Basic parts and functions of electromechanical relays include:

1. Frame: Heavy-duty frame that contains and supports the parts of the relay.
2. Coil: Wire is wound around a metal core. The coil of wire causes an electromagnetic field.
3. Armature: A relays moving part. The armature opens and closes the contacts. An attached spring returns the armature to its original position.
4. Contacts: The conducting part of the switch that makes (closes) or breaks (opens) a circuit.

Relays involve two circuits: the energizing circuit and the contact circuit. The coil is on the energizing side; and the relays contacts are on the contact side. When a relays 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, which is formed so that the armature can pivot, while the other end opens and closes the contacts. Contacts come in a number of different configurations, depending on the number of Breaks, poles and Throws that make up the relay. For instance, relays might be described as Single-Pole, Single-Throw (SPST), or Double-Pole, Single-Throw (DPST). These terms will give an instant indication of the design and function of different types of relays.