Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 27)

Hardware
Installing Your Controller
1–11
Safety Considerations
Safety considerations are an important element of proper system installation.
Actively thinking about the safety of yourself and others, as well as the condition of
your equipment, is of primary importance. We recommend reviewing the following
safety considerations.
Disconnecting Main Power
Explosion Hazard — Do not replace components or disconnect equipment
unless power has been switched off and the area is known to be
non-hazardous.
The main power disconnect switch should be located where operators and
maintenance personnel have quick and easy access to it. In addition to
disconnecting electrical power, all other sources of power (pneumatic and hydraulic)
should be de-energized before working on a machine or process controlled by a
controller.
Safety Circuits
Explosion Hazard — Do not connect or disconnect connectors while circuit is
live unless area is known to be non-hazardous.
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.