Rockwell Automation 1768-PA3_PB3 CompactLogix Power Supplies Installation Instructions - Manual (Page 11)

1768 CompactLogix Power Supplies 11
Publication 1768-IN001B-EN-P - July 2006
Safety Circuits
Power Considerations
This section describes power considerations you should take into account for the
CompactLogix I/O system.
Power Distribution
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. We recommend
that the controller remain powered even when the master control relay is
de-energized.
Avoid the delay of power supply shut-down by wiring the master control relay to
remove power from the devices instead of the 1768 power supply. Power the dc
power supply directly from the fused secondary of the transformer. Connect power
to the dc input and output circuits through a set of master control relay contacts.
WARNING
Explosion Hazard - Do not connect or disconnect connectors while circuit is
live.
ATTENTION
Circuits installed on the machine for safety reasons, like overtravel limit
switches, stop push buttons, and interlocks, should always be hard-wired
directly to the master control relay. These devices must be wired in series so
that when any one device opens, the master control relay is de-energized,
thereby removing power to the machine. Never alter these circuits to defeat
their function. Serious injury or machine damage could result.