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Learning Objectives
After this section, the students will be able to:• Describe the Emergency Stop Function and
requirements• Describe the three Stop Categories• List two common E-Stop devices and describe
their requirements
Emergency Stop Function
Covered in NFPA 79, EN 60204-1, and EN 13850
• Shall override all other functions
• Stop machine as quickly as possible without creating other hazards
• Reset shall not initiate restart
• Not a substitute for other safeguarding
Stop Categories
• Category 0– Remove power immediately.
• Category 1– Ramp machine to zero speed then remove power– Typical P&G E-Stop for servo machines– Need time delay safety relay (or safety PLC)
• Category 2– Ramp line to zero speed leave power on
• Every machine must have a cat. 0 stop– May be done by E-stop or Machine Main Disconnect
E-stop Devices
• Common types include:
– Push-buttons
– Pull-cord switches• Devices shall be positive opening• E-Stop actuators shall be colored Red with a Yellow
background
Safety E-Stop Device Requirements
Safety rated Emergency Stop Pushbuttons:
– shall have normally closed, positive- opening contact(s) (I.e. 1 for single channel with monitoring, 2 for control reliable) .
– for control reliable applications with removable contact blocks, shall have the two contacts on separate contact blocks.
– shall be red mushroom, 40 mm minimum diameter, with detent, requiring manual reset after actuation. Yellow Background
E-Stop Protection Devices
• Must be continuously operable and readily accessible by all operators– No covers are allowed
• Located at each operator control station, as well as at other locations as determined by the risk assessment
• Measures against inadvertent actuation should not impair its accessibility
If Button Protection is Needed
• Re-orient or relocate is best option• If needed, a protective device around the
button can be installed:– Must maintain a 120mm diameter clear area
around button– Cannot extend above the plane defined by the pressed button– P&G preference is 2 small bars above and below
E-Stop Pull Cord Device
• Pull Cord Switches
In order to meet Category 3, Pull Switches MUST be of the taut-line style.
Other versions cannot detect broken or cut cables.