Rockwell Automation Publication 2711P-TD001D-EN-P - February 2011
Wiring and Grounding Guidelines for PanelView Plus Terminals
27
How to Avoid Grounding
Problems
This section provides details on how to avoid grounding problems:
•
Multiple Ground Connections
•
High Current from Multiple Ground Connections
•
Ground Shift Problem
•
Ground Reference Problem
Multiple Ground Connections
It is important to avoid multiple ground connections with nonisolated and
isolated PanelView Plus terminals.
Nonisolated DC PanelView Plus Terminals
The internal DC power supply of the nonisolated PanelView Plus terminals does
not isolate the output voltages from the input voltages. On some PanelView Plus
terminals, DC- is internally connected to functional earth/ground (and chassis).
If another device by using the same power source has a DC- common to the
earth/ground connection, then two parallel-current paths exist:
•
One path leads from the DC- of the PanelView Plus terminal to the DC-
common of the other grounded device.
•
One path leads from the earth/ground terminal of the PanelView Plus
terminal to the earth/ground connection of the other grounded device.
A ground loop occurs in a system with parallel ground paths. A ground loop can
cause excessive current to flow in the PanelView Plus terminal. Excessive current
flow can damage the PanelView Plus terminal.
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Circuitry
Circuitry
+24V DC
Power
Common
Ground Loop
DC Power Supply
Circuitry
Circuitry
PanelView Plus
Terminal
PanelView Plus or
Other Grounded
Equipment
DC Power Supply
+24V DC
Power
Common
In+
In-
In+
In-
DC+
DC-
DC+
DC-
Isolated
DC-to-DC Converter
Isolated
DC-to-DC Converter
PanelView Plus
Terminal
PanelView Plus or
Other Nonisolated
Grounded Equipment