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
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.