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.

Common Types of Relays
Relay Operating Diagram
Common Types of Relays, Applications,
Relay basic circuit symbol

Relay Electrical Contact Forms




NO: Normally open (“make”) NC: Normally closed (“break“)

Two terminals which can be connected or disconnected.




CO: Change-Over (“break before make“)

A common terminal connects to either of two others, never connecting to both simultaneously.




Equivalent to a pair of SPST switches or relays actuated by a single coil.




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.


  • 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

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