Rockwell Automation 1763 MicroLogix 1100 Programmable Controllers User Manual - Manual (Page 25)

Publication 1763-UM001D-EN-P - March 2011
Installing Your Controller 23
Power Distribution
There are some points about power distribution that you should know:
• The master control relay must be able to inhibit all machine motion by
removing power to the machine I/O devices when the relay is
de-energized. It is recommended that the controller remain powered
even when the master control relay is de-energized.
• If you are using a DC power supply, interrupt the load side rather than
the AC line power. This avoids the additional delay of power supply
turn-off. The DC power supply should be powered directly from the
fused secondary of the transformer. Power to the DC input and output
circuits should be connected through a set of master control relay
contacts.
Periodic Tests of Master Control Relay Circuit
Any part can fail, including the switches in a master control relay circuit. The
failure of one of these switches would most likely cause an open circuit, which
would be a safe power-off failure. However, if one of these switches shorts
out, it no longer provides any safety protection. These switches should be
tested periodically to assure they will stop machine motion when needed.