Rockwell Automation Publication 2711P-TD001D-EN-P - February 2011
32
Wiring and Grounding Guidelines for PanelView Plus Terminals
Ground Reference Problem
A ground reference problem can occur if the equipment communicating with the
PanelView Plus terminal, using nonisolated communication lines on both ends, is
referenced away from earth ground by its power supply. Some systems have
voltages other than +24V, such as -24V DC. The communication equipment
might use these connections:
•
+24V DC input is connected to the power supply common.
•
Common is connected to the -24V DC power supply.
These connections p24V DC across the communication equipment
power supply and do not present a problem with the communication equipment
alone. However, when the communication equipment is connected to the
PanelView Plus terminal, the -24V DC power supply is shorted to the device’s
DC- and earth ground. High or sustained current in the PanelView Plus terminal
can damage the device. Use communication lines that are isolated on at least
one end.
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Communication Equipment
Nonisolated Comms Port
Isolated Communication
Nonisolated Communication
PanelView Plus
Nonisolated
Comms Port
DC Power Supply
User -24V Power Supply
Power Common
+24V DC
24V DC
OV
DC +
DC -
+24V
- 24V DC
Circuitry
Comms
Comms
Circuitry
User -24V Power Supply
DC Power Supply
Power Common
+24V DC
Circuitry
Comms
Circuitry
24V DC
PanelView Plus
Terminal
Isolated
Communication
Communication Equipment
+24V
DC +
DC -
OV
- 24V DC