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

Yes, it is possible to use a "conventional" limit switch (i.e. non-safety specific) 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, it may still be useful to use a specific safety switch. We used to sell a range for this purpose that could be recognised by its red colour. They had a plate that prevents access to the screws. This plate was attached using "5 lobe torque" safety screws, with a special fixing tool  supplied with the product. We no longer sell sensors and limit switches. For information on the above, please contact telemecaniquesensors.

Julkaistu:Schneider Electric Suomi