Cutler-Hammer D320 PLC, User Manual

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D320 PLC User's Manual
System Design Considerations
Power Supply Wiring
Physical and Electrical Isolation of Power Supplies
When wiring the PLC, external control I/O, and large power equipment such as motors, each system
should be electrically separated as shown:
Interlock Circuit and Emergency Stop Circuit (Safety measures in
system design)
In any PLC application, abnormal and potentially dangerous operation can occur. These system
malfunctions may result from power surges, brownouts, blackouts, shorted or opened I/O devices, or
any type of system component failure. Any errors of the PLC, the external power source, and/or
external devices can cause a system malfunction. The potentially dangerous effects of these errors on
the whole system can be prevented with proper safety precautions. The use of properly designed safety
circuits external to the PLC will protect against both equipment damage and human injury.
Interlock Circuit
An interlock circuit can control and prevent problems such as those caused by unexpected or reversed
operation of a motor. Install the interlock circuit external to the PLC control wiring and circuitry.
Emergency Stop Circuit
Every industrial control application involving electrical or moving parts should be wired with an
emergency stop circuit. The emergency stop circuit turns off the power immediately to all output
devices in the system. The emergency stop circuit should provide independent power cutoff from the
PLC system.
Power
Device
External
I/O device
PLC
Main power
source
Isolation transformer