Cutler-Hammer D320 PLC, User Manual

Page: 196 / 258

184
D320 PLC User's Manual
Advised Installation Practices
Shield the PLC
The most common method of shielding, is to install the PLC inside a grounded steel enclosure.
Proper Cable Selection
Use twisted, shielded-pair cable for the power cable and field wiring. Properly terminate the shields of
all cables to a single-point high-quality ground. (See section on shielding.)
Ground the PLC
The purpose of grounding the PLC is to protect the electronic equipment from electric shock and
harmful noise.
To ground the PLC, connect a 12 to 16 gauge wire from the frame ground terminal strip screw of the
power supply to a high quality earth ground (less then 2
Ω ). Since electrical currents always take the
path of least resistance, the noise currents induced by a magnetic field will flow through the PLC frame
ground terminal screw to earth ground. This essentially draws the noise away from the PLC modules.
The most effective method of grounding the PLC frame is to ground the PLC independent of other
equipment. Avoid grounding the PLC through a daisy chain of wire connections with other equipment.
See figures below for good and bad examples:
The length of the ground cable should not exceed 65 feet (20 m). For best results, the resistance of the
ground cable should be less than 2
Ω
. If single grounding is not possible, connect the frame ground
terminal of the PLC power supply to the equipment panel metal chassis via one of the PLC rack panel
base mounting screws.
PLC Others
PLC Others Others PLC