User Manual

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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Wiring 2019-05-15
6.7 EMC compliant wiring
Please refer also to Section 5.3 "EMC compliant control panel".
In control panels or buildings where severe electromagnetic interference (EMI) is likely,
devices susceptible to interference can be better protected by observing the following
rules for wiring:
• Inside the control panel the connection terminals and cable trunking for unscreened
conductors must be routed separately from screened conductors.
• Avoid cable loops.
• Provide sufficient space for correct connection of the cable screens.
• Connect cable screens directly to the control panel at the point of entry into the
control panel. Leave the screen intact up to the module.
• Make the control panel part of the equipotential bonding system in the building.
When organizing the cable trunking, ensure that any cables emitting high levels of
interference are routed separately from cables susceptible to interference.
• Interference-emitting cables: Motor cables, energy cables.
• Interference-susceptible cables: Control cables, low voltage cable, interface cables,
LAN cables, digital and analog signal cables.
• Both categories of cable can be routed in the same cable trunking, but in separate
compartments.
• In the absence of partitioned trunking enclosed on three sides, the interference-
emitting cables must be separated from other cables by at least 150 mm, or routed in
separate trunking.
• Where interference-emitting cables intersect with cables which are susceptible to
interference, they should cross at right-angles.
• Follow the recommendations of the manufacturer when selecting screened or
unscreened cable. In general, unscreened, twisted-pair cable has adequate EMC
properties for building services applications (including data applications).
• For the island bus (conductors CS and CD), unscreened round cord is admissible.
• Unscreened cables have the added advantage that there is no need for concern
about earth coupling.
Screening enhances the EMC immunity. However, the following rules must be
observed:
• The purpose of the earthing procedure (common reference point) is to dissipate and
short-circuit interference voltages conducted by the cable screens.
• Careful attention must be paid to the earthing strategy in order to avoid earth looping
or differences in potential.
• To avoid low frequency interference, screens must be earthed on one end only.
• To avoid high frequency interference, screens must be connected at both ends to the
earth mass. However, equipotential bonding via the cable screens must be avoided.
In the absence of equipotential bonding (e.g. with connections between buildings
over large distances) a separate equipotential bonding system must be installed.
Alternative: hard wired earthing on one side, via a capacitor on the other side.
• For effective screening, it is important that the cable screen is properly connected to
the earth mass (see below).
• Island bus expansion: refer to section 10.6.
Wiring rules
Control panel wiring
Building wiring
Different types of cab
le in
the same trunking
Cable types
Segregating the cables
Unscreened cable
Screened cable