Contactor

Contactor cut-away animation with AUX

Pneumatic by-passing contactors of electric locomotive VL11

Contactor

A contactor is an electrically-controlled switch used for switching an electrical power circuit. A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current.

Design and Operation[edit | edit source]

Contactors come in many forms with varying capacities and features. Unlike relays, contactors are designed to be directly connected to high-current load devices. Contactors range from those having a breaking current of several amperes to thousands of amperes and 24 V DC to many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side.

Components[edit | edit source]

A contactor typically consists of:

An electromagnet (or coil) which provides the force to close the contacts.
A set of contacts that carry the current and withstand the arc when opening and closing.
An enclosure to protect the contacts and the electromagnet from dust, oil, and other contaminants.

Types of Contacts[edit | edit source]

Contactors use different types of contacts depending on the application:

Normally Open (NO) contacts: These contacts close when the contactor is energized.
Normally Closed (NC) contacts: These contacts open when the contactor is energized.
Auxiliary contacts: These are used in control circuits and are not designed to carry high currents.