User guide

Wiring and Cabling
890 USE 108 00 August 2001 135
Functional
Grounding
Functional grounding diverts and neutralizes extraneous electrical signals that
interfere with orderly controller logic voltage levels and clock pulses. Extraneous
noise can be generated by electrical motors, variable frequency drives, solenoids,
etc., and can radiate through the air as well as be conducted through chassis metal
and wiring.
The indicated point on the DIN rail that supports the primary DTA 200 backplane is
the control system’s functional ground point. This location indicated on the DIN rail
is also the collection point for bonding, system reference, and system RFI/EMI
shielding.
If you are mounting multiple Compact Controllers on separate DIN rails and you are
not mounting them on a plate in a metal cabinet or on a 19 in EIA rack, connect the
primary rails to a common bonding point with braid or heavy gauge solid conductor
wire. Always avoid daisy chaining ground wiring.
Tying multiple PLCs to a common functional ground is shown in the following figure.
If you are not using a dedicated equipotential bonding path, you should tie the
primary DIN rail to the building’s structural metal via mounting hardware, metal
conductor, or metal braid installed without bends or loops.
DTA 200
DTA 200 DTA 201
DTA 201
DTA 201
DTA 201
CPU P120
Protective Ground Points
on Primary DIN Rails
Building Metal or
Bonding Surface