High Current From Multiple Ground Connections - Allen-Bradley 2711P Technical Data Manual

Single Power Supply Provides Power to Multiple Devices
DC Power Supply
> > >
+24V DC
Power
> >
Common
DC+ DC-
Circuitry
PanelView Plus
Terminal
Rockwell Automation Publication 2711P-TD001D-EN-P - February 2011

High Current from Multiple Ground Connections

The illustration below shows one 24V DC power supply providing power to a
DC motor and a nonisolated PanelView Plus terminal. Because DC- is
connected to earth/ground in the motor and the PanelView Plus terminal, two
paths exist for the current to return to the power supply. The motor current can
flow through the system's earth/ground structure into the PanelView Plus
terminal, and back to the power supply.
Because the system's earth/ground structure has a lower impedance than the
common wiring, the motor current will flow through earth/ground and the
PanelView Plus terminal. The motor current could damage the terminal.
Nonisolated DC PanelView Plus Terminals
Use a separate power supply for each device; one to power the nonisolated
PanelView Plus terminal and one to power the motor. The current will return to
each power supply through the DC- wiring instead of the earth/ground
structure.
>
DC Motor
>
Motor Common
tied to Earth
> >
>
Wiring and Grounding Guidelines for PanelView Plus Terminals
Separate Power Supply for Each Device
2711P-RSACDIN DC Power Supply
+24V DC
Power
Common
DC+ DC-
Circuitry
PanelView Plus
Terminal
29
+24V DC
Power
Common
DC Motor
Motor Common
Tied to Earth