Rockwell Automation 8520 9/Series CNC Integration Maintenance Manual Documentation Set - Manual (Page 240)

Section 4D
Power Distribution and Wiring Guidelines
4D-10
All components and modules must be correctly grounded to protect against
electrical shock hazards. Proper grounding also helps to reduce the effect
of electrical noise by isolating induced noise voltages to individual ground
wires and shunting them to ground.
There are two types of grounds used in electrical system design, chassis
and earth. Chassis ground is defined as the internal ground of a cabinet.
Earth ground is defined as the central ground for all electrical equipment
and ac power within any factory.
For the chassis ground use a conductor such as the control cabinet or the
cabinet’s grounding bus bar. To provide good conductivity when the
cabinet is used as the conductor, remove rust and any coating from the area
of the cabinet that will be a contact point for the ground cables. Each
component installed in the cabinet will have a separate grounding cable
connected to the conductor.
Each electrical cabinet requires two separate connections from the cabinet
to the earth ground:
from the chassis ground -- each component installed in a cabinet is
connected to the cabinet’s chassis ground. The cabinet chassis ground is
connected to the earth ground by a single grounding cable.
from the cabinet -- each cabinet is connected separately to the earth
ground.
ATTENTION: To guard against damage to the machine, do not
interconnect chassis ground wires between the components.
This would place ground wires in series and cause their noise
voltages to be additive. The resulting increased noise energy
can interfere with proper control and machine functions.
A general system grounding diagram, which shows both chassis ground
and earth ground, is shown in Figure 5A.21.
4D.3
Protective Grounding