Allen-Bradley SLC 500 Notice D'installation page 9

1746-P3 Wiring Considerations
The information below describes special wiring considerations for the 1746-P3.
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
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, -A7, -A10, and -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, -A7, -A10, and
-A13) with a manufacture date of November 1992 or later do not
have this resistor. SLC 500 Series B chassis have a 1MΩ resistor
that limits the current between logic ground and chassis ground.
SLC 500™ Power Supplies
SLC 500 Chassis
Processor
DH-485
Port
SLC Logic Ground
Earth
Ground
Publication 1746-IN004D-MU-P - May 2003
9