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How To Select A Contactor For Your Application

by Ed Kenny | Oct 05, 2016

Although the contactor is probably one of the most common components in an industrial / motor control application, selecting one correctly requires detailed application information to be provided.

There are 3 key elements to a contactor:                                                    

  1. Main contacts (also referred to as main poles)

  2. Auxiliary contacts

  3. Coil (part of the electromagnet used to energize the contactor).

Each of these elements should be fully specified based on the application. Understanding these main elements will take you a long way in identifying the proper contactor.

1. Main pole selection criteria:

  • How many required in either normally open (N/O) or normally closed (N/C) format?

  • Current rating in amps.

  •  Voltage rating                           

  • Duty In the absence of a specific duty, a full description of the nature of the electrical load (e.g. lighting, resistive heating etc), making current, breaking current and continuous current through the contacts.

2. Auxiliary contacts selection criteria:

  • How many required in either normally open (N/O) or normally closed (N/C) format? Possibility of time delayed auxiliary contacts with certain product ranges.

  • If not used in standard low power signaling application, details as per main poles required.

3. Coil selection criteria:

  • Voltage of coil (Note: The coil is often a different voltage to the main poles).

  •  AC or DC voltage; Frequency of coil if AC. If DC coil, is low consumption required

Depending on your application, additional ancillary parts and accessories are available and may be required.

To determine if you need these, additional information should be considered:

  • Is the contactor to be enclosed, i.e. is an enclosed motor starter required?

  • Specific design requirements

  • Number of operations per hour

  • Latching operation

  • Environmental considerations such as ambient temperature etc.

You should also review if any ancillary parts are required such as mechanical interlocks, busbars, thermal overload relays or motor protection circuit breakers. Additional parameters and options available include:

  • Operating and Control Voltage

  • Horse power/Amps/KVAR

  • No. of Phases & No. of Poles

  • Bidirectional

  • Motor

  • Capacitor

  • Transformer

  • Vacuum vs. Air-break

  • Ambient Temperature

  • Standards (UL, IEC, NEMA)

Selecting the proper contactor for your application requires a thorough understanding of your situational needs and demands. A member of our Application Support Team would be happy to assist should you have questions.

To learn more, please Download our contactor brochure.