Rockwell Automation 1747-L5xx SLC 500 Modular Hardware Style User Manual - Manual (Page 67)

Publication 1747-UM011G-EN-P - June 2008
System Installation Recommendations 67
Whenever any of the emergency-stop switches are opened, power to input and
output devices is stopped.
When you use the master control relay to remove power from the external I/O
circuits, power continues to be provided to the controller’s power supply so
that diagnostic indicators on the processor can still be observed.
The master control relay is not a substitute for a disconnect to the controller. It
is intended for any situation where the operator must quickly de-energize I/O
devices only. When inspecting or installing terminal connections, replacing
output fuses, or working on equipment within the enclosure, use the
disconnect to shut off power to the rest of the system.
Emergency-Stop Switches
Adhere to the following points concerning emergency-stop switches.
• Do not program emergency-stop switches in the controller program.
Any emergency-stop switch should turn off all machine power by
turning off the master control relay.
• Observe all applicable local codes concerning the placement and
labeling of emergency-stop switches.
• Install emergency-stop switches and the master control relay in your
system. Make certain that relay contacts have a sufficient rating for your
application. Emergency-stop switches must be easy to reach. See the
schematic on page 69.
IMPORTANT
The operator must not control the master control relay with the
processor. Provide the operator with the safety of a direct
connection between an emergency-stop switch and the master
control relay.