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What information is required to correctly select (specify) a contactor?

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;

  • Main contacts (also referred to as main poles)
  • Auxiliary contacts
  • Coil (part of the electromagnet used to energise the contactor).
Each of these elements should be fully specified based on the application;

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 in AC or DC
  • Duty (either AC1, AC3, DC1- DC5 etc). 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 (available for certain ratings of TeSys D and TeSys K contactors). 
Any additional information available should be provided, such as;

  • Is the contactor to be enclosed, i.e. is an enclosed motor starter required?
  • Specific design requirements (e.g. Modular)
  • Number of operations per hour
  • latching operation
  • Environmental considerations such as ambient temperature etc.
  • Are any ancillary parts required such as mechanical interlocks, busbars, thermal overload relays or motor protection circuit breakers?

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