Common Types of Relays, Applications, Electrical Contact Forms

Relays are electrically operated switches. A low-voltage, low-current control signal is used to operate a set of contacts that quickly and safely switch larger voltages and currents. Traditionally, the control signal energizes an electromagnet to open or close the contacts. Solid-state relays using semiconductor technology for the control and switching functions are also available. [caption id="attachment_15802" align="aligncenter" width="427"] Relay Operating Diagram[/caption] [caption id="attachment_15803" align="aligncenter" width="352"] Relay basic circuit symbol[/caption]

Relay Electrical Contact Forms

SPST Single-Pole Single-Throw NO: Normally open (“make”) NC: Normally closed (“break“) Two terminals which can be connected or disconnected.	SPDT Single-Pole Double-Throw CO: Change-Over (“break before make“) A common terminal connects to either of two others, never connecting to both simultaneously.	DPST Double-Pole Single-Throw Equivalent to a pair of SPST switches or relays actuated by a single coil.	DPDT Double-Pole Double-Throw Equivalent to two SPDT switches or relays actuated by a single coil.

Common Relay Types

There are five common types of relays widely used in different applications. Contactor

• A special case of relay designed to switch high-current loads such as electric motors safely.
• Fast operating speed minimizes arcing caused by the load.

Solid-State Relay

• Similar to an electromechanical relay but has no moving parts and instead uses optical or electronic means to switch the load.
• Care is needed when used with AC.

Latching Relay

• Maintains either contact position indefinitely without power applied to the coil.
• It consumes power only for an instant while the relay is being switched.

Automotive Relay

• Robust relays working with 12V or 24V.
• The starter relay controls the high current of the cranking motor by small wiring and contacts in the ignition key.

AC Relay Three basic types:

• DC relay with rectifier
• Phase relay with two coils on separate cores
• Split-pole relay uses a short-cut coil. The induced short-cut current is out-of-phase to the control current.

Please visit the following article for detailed insight into how different relays operate. Electromechanical Relays: Types and Operating Mechanism