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Can I use a "conventional" limit switch for safety applications?

Yes, it is possible to use a "conventional" limit switch for safety applications, as long as the switch is "positive action"

Definition of positive action:
 

  • A limit switch is said to be positive action if its normally closed (NC) contacts can be changed to the open position with certainty
     
  • The symbol indicating this type of operation is an arrow in a circle.

     Contact with Positive Opening
 

Notes:

Other conditions may be necessary for integrating a limit switch in a safety application:

  • Redundancy of contacts of NC contacts
  • Integrity of the sensor, the contacts in the sensor must not be modified.
  • For these reasons Schneider has developed a range of safety limit switches, that can be recognised by their red colour.
  • They have a plate that prevents access to the screws. This plate is attached using "5 lobe torque" safety screws, and the fixing tool is supplied with the product.
FA24894  |  05-Mar-2014  | Safety
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