Publication 1763-UM001E-EN-P - June 2015
Installing Your Controller 27
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.
Using Emergency-Stop Switches
When using emergency-stop switches, adhere to the following points:
• 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.
• In the following illustration, input and output circuits are shown with
MCR protection. However, in most applications, only output circuits
require MCR protection.
The following illustrations show the Master Control Relay wired in a grounded
system.
Do not control the master control relay with the
controller. Provide the operator with the safety of a direct
connection between an emergency-stop switch and the
master control relay.
In most applications input circuits do not require MCR
protection; however, if you need to remove power from all
field devices, you must include MCR contacts in series with
input power wiring.
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