Rockwell Automation 1747-ACNR15 ControlNet Adapter Module User Manual - Manual (Page 104)

Publication 1747-UM003A-EN-P
B-12 Understanding Your SLC 500/1746 Control System
Place the main power disconnect switch where operators and maintenance
personnel have quick and easy access to it. If you mount a disconnect switch
inside the system enclosure, place the switch operating handle on the outside of
the enclosure, so that you can disconnect power without opening the
enclosure.
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 system’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.
IMPORTANT
If you are using a dc power supply, interrupt the dc side
rather than the ac side to avoid the additional delay of
power supply turn-on and turn-off. The dc power supply
should receive its power directly from the fused secondary
of the transformer. Connect the power to the dc input and
output circuits through a set of master control relay
contacts.
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.