Internal Enclosure Grounding; Equi-Potential Grounding; Communications And Shielded Cables - Automation Direct DL205 Manual

A–6
European Union Directives
Internal Enclosure
Grounding
Equi–potential
Grounding
Communications
and Shielded
Cables
DL205 Installation and I/O Manual, Rev. B
A heavy-duty star earth terminal block should be provided in every cubicle for the
connection of all earth ground straps, protective earth ground connections, mains
filter earth ground wires, and mechanical assembly earth ground connections. This
should be installed to comply with safety and EMC requirements, local standards, and
the requirements found in IEC 1000–5–2.The Machinery Directive also requires that
the common terminals of PLC input modules, and common supply side of loads driven
from PLC output modules should be connected to the protective earth ground
terminal.
Key
Adequate site earth grounding must be provided for equipment containing modern
electronic circuitry. The use of isolated earth electrodes for electronic systems is
forbidden in some countries. Make sure you check any requirements for your
particular destination. IEC 1000–5–2 covers equi-potential bonding of earth grids
adequately, but special attention should be given to apparatus and control cubicles
that contain I/O devices, remote I/O racks, or have inter-system communications with
the primary PLC system enclosure. An equi-potential bond wire must be provided
alongside all serial communications cables, and to any separate items of the plant
which contain I/O devices connected to the PLC. The diagram shows an example
of four physical locations connected by a communications cable.
Screened
Cable
Î Î Î Î
Î Î Î Î
Equi-potential
Bond
Good quality 24 AWG minimum twisted-pair shielded cables, with overall foil and
braid shields are recommended for analog cabling and communications cabling
outside of the PLC enclosure.
Serial Communication Cable
Equi-potential Bond
Conductive
Adapter
Serial
I/O
To Earth
Block
Control Cubicle