Safety issue

Discussion in 'Feedback and Suggestions' started by Unregistered, Dec 17, 2007.

  1. Unregistered

    Thread Starter Guest

    The correct way to implement a STOP pushbutton is to : (i) hardwire it onto a Normally Closed contact and (ii) Program it as a Normally Open contact.
    If it's implemented as you've shown ie. hardwired to a Normally Open contact and programmed as a (NOT) normally Closed, then it's unsafe because if a cable becomes detached from the Stop Pushbutton there will be no indication on the ladder logic.It will only become apparent when the stop pushbutton is pressed (possibly as an emergency) and nothing happens.
  2. cumesoftware

    Senior Member

    Apr 27, 2007
    Indeed, stop buttons must be normally closed, so a break in the wiring close to it will cause the machine to stop, instead of not allowing it to stop when the button is pressed.
  3. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    To what diagram are you refering? If I search on "stop button" I find this image:

    And the next two following images in volume 4, Chapter 6

    These (3) images seem to have the "stop button" as a nornally closed contact. as you say it should be. Am I on the the wrong image? Am I missing something? If there is a safety issue in LIEC we would like to correct it.
  4. Dave

    Retired Moderator

    Nov 17, 2003
  5. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004