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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Principles of electrical design 2019-05-15
10.14 Wiring for Relay outputs
• External fuse of max. T 10 A for protection of the PCB tracks.
• The maximum load of the relay contracts must be observed (see data sheets for the
corresponding devices). It may require a fusing <10 A.
• Relays have volt-free relay contacts.
The mains voltage / switching voltage (AC 230 V / AC/DC 24 V) must be supplied as
an external voltage to the terminals.
• The sizing and fusing of the lines are oriented to overall load and local regulations.
Actuators up to 100 VA: Lengths of up to 300 m / 1000 ft are admissible.
Wiring must comply with local regulations.
Taking account of the permissible voltage drop, the cable between the switching
outputs and the equipment to be switched may be up to 300 m / 1000 ft long.
The permissible lengths are calculated as follows:
Voltage drop of max. 7 % (1.68 V) on the AC 24 V operating voltage for the actuator.
Cable cross section Cable length for AC 24 V
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.
Use cable cross section suited for 10 A according to local regulation.
Cable length
AC 230 V
Cable length AC 24 V
Note
Cable cross section