Installlation
2-10
SIMATIC 505–2556 Installation and Operation Guide
Configuring the Module (continued)
Siemens
recommends that all signal wires be shielded twisted–pair with foil
wrap shield and a separate drain wire and that they be installed in a
metallic conduit. Use Belden cable 8761 or equivalent whcih contains a foil
wrap shield and a separate drain wire. The shield and the foil wrap should
be twisted together and should be terminated at only one end. The other
end should be left in an open circuit condition. Siemens recommends that
the shield be terminated at the PLC end of signal wire. Special components
are installed on the module to aid in the rejection of noise.
When entering the industrial cabinet the shield wires should be routed from
the main terminal strip all the way to the PLC. Signal leads that do not
maintain a shield from the terminal strip to the PLC act as antennas and
are susceptible to radiated and conducted emissions in the cabinet.
Unprotected cables may introduce measurement errors in the module.
The front connector on the module contains a G terminal whcih may be used
for the shield wire if the installation is in a noise free environment. If the
installation is in an extremely noisy environment Siemens strongly
recommends that the shield wires be terminated tothe PLC chassis ground.
This product has been exhaustively tested to maximize its ability to reject
noise from inductive sources as well as showering arcs, fast transients and
other high frequency generators and has determined that the best
performance results from connecting all shield wires together at the PLC
module and terminating this single wire to the chassis ground with a large
current capacity conductor
. The PLC chassis should then be wired to earth
ground with a large current capacity conductor
. Siemens recommends using
a #8 gauge wire from the PLC chassis to the earth ground connection.
Connecting the
Shield W
iring
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