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Siemens Desigo Desigo Room automation - Engineering, mounting and installation CM111043en_14
Smart Infrastructure MS/TP networks 2020-10-30
10.2 Technical data BACnet MS/TP
Communications on BACnet MS/TP networks take place over EIA-485 physical
media.
· Desigo TRA devices use the 3-wire interface without noise suppression.
Therefore, the cables must provide noise protection. This is guaranteed by the
reference wire and the shielding.
· The interface is protected against short circuit, wrong polarity and faulty wiring
with AC 24 V. However, communications do not work with wrong polarity.
Transmission medium
(bus cable)
1.5-Pair (1 TP & 1 conductor)
with overall Shield and drain wire
Pair
1)
Gauge Min. 0.2 mm
2
(24 AWG) stranded or solid
2)
Capacitance
conductor to
conductor
conductor to shield
Max. 41 pF/m / 12.5 pF/ft
Max. 79 pF/m / 24 pF/ft
Twists Min. 13/m / 4/ ft
Reference wire ( )
Gauge Min. 0.2 mm
2
/ 24 AWG stranded, or solid
Twists with pair Min. 13/m / 4/ ft
Shield 100% overall foil with drain wire
3)
Voltage rating 300 V
4)
Temperature rating 75°C / 167 °F or higher
Standards EU CE Mark
2011/65/EU (ROHS II)
2002/96/EC (WEE)
2003/11/EC (BFR)
MII Order #39 (China RoHS)
1)
Stranded conductors are easier to connect in narrow places.
Less risk of breaking in case of vibrations
2)
Higher capacitance must be compensated by
– smaller network length or
– smaller number of devices or
– smaller Baud rate.
3)
Infrastructure network cabling is normally separated from mains cables, 30 V
would be sufficient. But in cabinets, very small distance to main cables,
therefore 300 V or even 600 V is required.
National standards may also require 300 V.
4)
As the room automation stations require less than 50 °C, cabling in the
cabinet can have the same rating. But outside the cabinet, avoid hot places
like lighting troughs.
3-wire RS-485 network
interface
Cable specifications