Assembly and Installation
Chapter 3
333
Figure 3.32
Cable Shield Connection
Ground Shield at
I/O Chassis
Mounting Bold
Shield and Drain
Twisted into
Single Strand
Field
Wiring Arm
17798
The shield cable at the field devices can be configured as described in
Figure 3.33.
When bringing AC power into the enclosure, the raceway or conduit may be an
equipment grounding conductor which should be connected to the ground bus
on the back panel. Ground loops may introduce objectionable ground currents
causing faulty operation of the Programmable Controller. If the use of multiple
grounding connections results in faulty operation, refer to Article 250-21 of the
National Electric Code. This Article recommends methods of reducing
objectionable ground currents. Local Codes and Ordinances dictate which earth
grounding method is permissible.
When AC power is supplied as a separately derived system through an isolation
stepdown transformer, it can be connected as a grounded AC system or an
ungrounded AC system. In a grounded AC system, one side of the transformer
secondary must be connected to the ground bus (Figure 3-34).
In an ungrounded AC system, one side of the ground fault indicator test switch
must be connected to the ground bus (Figure 3.35).
Incoming AC Wiring
Guidelines
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