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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