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Siemens
Desigo TRA Engineering, mounting and installation
CM111043en_09
Building Technologies
Wiring of power lines
2016-02-22
Power consumption of the triacs on DXR2 AC 24 V
Per triac
6 VA / 250 mA
Unconfigured triac
(Reserve for later configuration)
6 VA / 250 mA
Thermal actuators with a starting power of 6 VA (not pre-heated):
If driven by a 5...50% PWM signal, they only count for 3 VA.
Max. power consumption of DXR2 AC 24 V
Due to internal heat dissipation, the max. power consumption of the devices is
limited (sum of base load, KNX supply, field supply, and triacs):
Device
Max. power
Max. power with cold thermal actuators
DXR2.M11
58 VA / 2.416 A
94 VA / 3.917 A
DXR2.M12P 58 VA / 2.417 A
94 VA / 3.917 A
DXR2.E12P 60 VA / 2.5 A
96 VA / 4 A
DXR2.M18
70 VA / 2.917 A
96 VA / 4 A
DXR2.E18
72 VA / 3 A
96 VA / 4 A
6.3.4
AC 24 V power line cable lengths
The permissible voltage drop of 0.48 V (2%) on the power wire between the
transformer and the most distant power point (room automation station, power
supply module, bus connection module) is the basis for calculations.
The table below provides cable lengths and cable cross sections based on load.
Cable cross-section
Cable length
Power
5 VA
10 VA
20 VA
50 VA
100 VA
200 VA
2.50 mm
2
/
AWG14
135 m
440 ft
70 m
220 ft
35 m
110 ft
13 m
44 ft
7 m
22 ft
3 m
11 ft
1.50 mm
2
/
AWG16
85 m
280 ft
42 m
140 ft
21 m
70 ft
8 m
30 ft
4 m
15 ft
2 m
7 ft
1.00 mm
2
/
AWG18
55 m
180 ft
27 m
90 ft
13 m
45 ft
5 m
17 ft
3 m
9 ft
1 m
4 ft
The supply (AC 24 V) and return lines ( ) can each have the indicated lengths.
Each supply point (room automation stations/power supply module/bus
connection module) is either connected separately to the transformer's terminal
block (star wiring) or looped via the room automation station.
Power is added together for multiple back-to-back looped devices ("daisy chain")
which reduces the cable length accordingly.
Cables
may
be wired in parallel to increase the cross section.
In practice, the small level of permissible voltage drop off means that the
transformer must always be installed in close proximity to the TRA devices
and that any cascading powering of room automation stations is only
possible over short distances or at small outputs.
Notes
