For machinery such as conveyors, it is often more convenient and effective to use a cable pull device along the hazard area as the emergency stop device. These devices use a steel wire rope connected to latching pull switches so that pulling on the rope in any direction at any point along its length will trip the switch to cut off the machine power.
The Allen-Bradley Guardmaster 440J is a hand-operated grip style enabling device. Underneath the rubber boot, called the trigger switch, the 440J enabling device has two three-position switches. The contacts are closed when the actuator is in the mid-position (partly depressed). The contacts are open when the actuator is in the rest (released) position and in the fully pressed position. When transitioning from fully pressed to released, the contacts remain open. The 440J meets the requirements of IEC 60947-5-8:2006, which was written to describe the performance and design requirements of three-position enabling devices.
Emergency Stop devices provide increased reliability. E-stops with normally closed late break contacts comply with EN418 and IEC 947‑5‑5 standards. This means the operator will latch when actuated before the contacts will change state.
Application flexibility is offered with 2‑position push-pull or 2‑position push-pull/twist release configurations. Non-illuminated and illuminated operator options are available. Contact block versions are also available that provide IP2X finger-safe protection.
Rockwell Automation also offers Self-Monitoring™ contact blocks (SMCB) which feature enhanced E-stop safety for critical process control applications. The SMCB monitors whether or not it is properly installed on the operator so that the normally closed contacts will open when the E-stop is actuated. If the SMCB is separated from the operator for any reason, the controlled circuit will automatically open.