User guide

Wiring and Cabling
134
890 USE 108 00 August 2001
System Bonding and Grounding
Overview As part of your installation procedure, provide the Compact system with
equipotential bonding of all inactive metal parts, protective grounding, functional
grounding, and system reference grounding.
Equipotential
Bonding
A conductive connection, or equipotential bond, must be made between the inactive
metal parts of all electronic equipment. Equipotential bonding provides protection
from electric shock, which can result from system faults or from dissimilar chassis
potentials due to site wiring. Bonding also prevents ground loops and conducted
noise from affecting the system. Building structural metal is normally used, but for
the best bonding quality, a separate and dedicated bonding path should be
established. Solid metal stock makes the best path, and metal braid installed with
minimum loops or bends is a second choice. Stranded heavy-gauge wire is not a
good choice because its reactive components present a high impedance at noise
frequencies. A dedicated bonding path or any bonding path other than structural
metal should be connected to the building metal at one point.
If a dedicated bonding path is not practical at your installation site, you may establish
the path using building structural metal or electrical wiring conduit. Lighting circuits,
vending machines, and other factory electrical equipment-such as variable
frequency drives-can generate interference that may be coupled to your system
equipment via building structural members. Equipment should be mounted as far as
possible away from these noise sources. Use toothed lockwashers at each
connection point to ensure good bare metal connections. Choose connection points
that are free from grease, oil, or dirt.
Protective
Grounding
To establish protective ground for a Compact Controller, connect ac source ground
wires (green or green/yellow) to the DIN rail on which the DTA 200 primary
backplane is mounted. This ground connection protects the operator from harmful
potentials that might be generated externally or from internal system faults through
contact with an exposed, noncircuit, metal surface. If your installation includes the
optional AS-P120-000 Power Supply, connect the ac source ground wire to the
middle terminal connector on that unit’s input power terminal strip (See A120 Power
Supplies, p. 177).