Preface
MicroLogix 1000 Programmable Controllers User Manual
1–12
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.
• 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 is 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.
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