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Siemens
Desigo TRA Engineering, mounting and installation
CM111043en_09
Building Technologies
Wiring of field devices (without bus)
2016-02-22
7.2
Wiring for Triac outputs AC 24 V
The following applies for wiring to actuating devices such as valves, damper
actuators or protection connected to the Triac outputs:
Use stranded, 2 or multiple core round cables, screened (standard off-the-shelf
installation cable).
Single wires may not be used.
Wiring may be laid together with power lines (AC 230 V).
They must be isolated from the power lines per regulations. Isolation must meet
PELV requirements.
Wiring cannot be led in the same cable as the power lines.
Cable length and cross section
Triacs are protected against overload.
Cable cross section
>= AWG20 / 0.75 mm
2
.
Cable length
<= 80 m / 260 ft (EM interference).
Use
cable cross section
suited for
10 A
according to local regulations
(
T 10 A
fuse in the power supply module / room automation station).
Cable length
<= 300 m / 1000 ft (EM interference).
Calculation is based on a voltage drop of 0.48 V = 2% of 24 V (the triac and the
PTC protection resistor have a voltage drop of 6%).
Cable cross section
Cable length
Power
1 VA
2 VA
5 VA
10 VA
20 VA
2.50 mm
2
/
AWG14
300 m
1000 ft
300 m
1000 ft
140 m
440 ft
70 m
220 ft
35 m
110 ft
1.50 mm
2
/
AWG16
300 m
1000 ft
210 m
700 ft
85 m
280 ft
42 m
140 ft
21 m
70 ft
1.00 mm
2
/
AWG18
270 m
880 ft
135 m
440 ft
50 m
180 ft
25 m
90 ft
13 m
45 ft
0.75 mm
2
/
AWG20
170 m
550 ft
85 m
275 ft
33 m
110 ft
16 m
55 ft
8 m
27 ft
The outgoing and return cables may
each
have the indicated length.
Power = permanent load. The higher starting current of thermal or motorized
actuators is admissible.
Cable material
Cable laying
DXR2... room automation
stations
PXC3 with TX-I/O triac
modules:
Caution!
Cable length
Notes
