Installation Instructions

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Siemens Desigo Room automation - Engineering, mounting and installation CM111043en_14
Smart Infrastructure Wiring of field devices (without bus) 2020-10-30
7.1.3 Active sensors and actuators DC 0 … 10 V
The permissible length of DC 10 V cables for signals, and of the cables to supply
the devices, have to be calculated on the following basis for each device (see also
the relevant device data sheets):
– Max. 7 % voltage drop (1.68 V) on the cables due to the sensor supply current.
Reason: to ensure sufficient voltage for the device supply.
– Active sensors: Measuring error of max. 0.5 % due to line resistance on the
measuring conductor (not critical, as the measuring current is only 0.1 mA)
– Active actuators: control signal error of max. 1 % due to line resistance on the
measuring conductor (not critical, as the measuring current is only 0.1 mA)
· Longer cables are permissible provided larger measuring errors are acceptable.
· If the device is supplied locally from a transformer, the signal cable can be up to
300 m / 1000 ft long (DXR2: 80 m / 260 ft) with a wire diameter of ³ 0.6 mm.
à The local transformer MUST NOT be earthed (earth loop)!
· DC 0…10 V actuators with DC 0…10 V feedback:
System neutral of output and feedback may be in the same conductor due to the
small current. However, output and feedback must be on the same device.
· In case of active sensors with AC 24 V supply, use cable cross section suited for
10 A according to local regulations (M 10 A fuse in the power supply module /
room automation station).
The maximum cable length is 300 m / 1000 ft (DXR2: 80 m / 260 ft).
The permissible length of the cables is calculated as follows: Voltage drop of max.
7 % (1.68 V) on the AC 24 V operating voltage for the sensor / actuator.
Cable cross section Cable length
Power
2 VA 5 VA 10 VA 20 VA 50 VA
2.50 mm
2
/ AWG14 300 m
1000 ft
300 m
1000 ft
235 m
770 ft
120 m
390 ft
47 m
150 ft
1.50 mm
2
/ AWG16 300 m
1000 ft
300 m
1000 ft
150 m
500 ft
75 m
250 ft
30 m
100 ft
1.00 mm
2
/ AWG18 300 m
1000 ft
185 m
600 ft
95 m
300 ft
50 m
150 ft
20 m
60 ft
0.75 mm
2
/ AWG20 290 m
960 ft
120 m
380 ft
60 m
190 ft
30 m
95 ft
12 m
40 ft
The outgoing and return cables may each have the indicated length.
Notes
Caution!
PXC3 with
TX
-
I/O
modules
Cable length for
devices with AC 24 V
Note