Contactor

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

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

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

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.

Applications

Contactors are used in various applications, including:

• Electric motor control
• Lighting control
• Heating, ventilation, and air conditioning (HVAC) systems
• Capacitor bank switching
• Welding machines

Advantages

• High current capacity
• Long operational life
• Reliable performance
• Can be controlled remotely

Disadvantages

• Can be bulky
• May require maintenance
• Can generate electrical noise

Related Pages

• Relay
• Circuit breaker
• Electromagnet
• Electric motor
• HVAC