Allen-Bradley SLC 500 Installation Instructions Manual page 11

1746-P3 Wiring Considerations
This information describes special wiring considerations for the 1746-P3 power
supply that are not labeled as revision (REV) B.
ATTENTION
!
External DC Power Source
+24V dc
DC Neut
Chassis
Ground
Earth Ground
IMPORTANT
Any voltage applied to the 1746-P3 DC NEUT terminal will be
present at the SLC logic ground and the processor DH-485 port.
To prevent unwanted potentials across the logic ground of the
controller and/or damage to the SLC chassis, the DC NEUTRAL
terminal of the external DC power source must be either
isolated from the SLC chassis ground or connected to earth
ground as shown in the following illustration.
1746-P3
Door
+24V dc
DC Neut
•
A jumper wire is
recommended between
the DC NEUT and Chassis
Ground of the external
power source.
SLC 500 series A chassis (1746-A4, 1746-A7, 1746-A10, and
1746-A13) manufactured before November 1992 have a resistor
between the logic ground and chassis ground as the drawing on
the following page illustrates. This resistor could be damaged if
the wiring recommendation described within the attention box
above is not followed. See the figure on the following page for
the location of the resistor. SLC 500 series A chassis (1746-A4,
1746-A7, 1746-A10, and 1746-A13) with a manufacture date of
November 1992 or later do not have this resistor. SLC 500 series
B chassis have a 1 MΩ resistor that limits the current between
logic ground and chassis ground.
SLC 500 Chassis
Processor
DH-485
Port
SLC Logic Ground
Earth
Ground
Publication 1746-IN004B-EN-P - March 2008
Installation Instructions 11