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Siemens
VAV compact controller KNX/PL-Link G..B181.1E/KN
CE1P3547en
Building Technologies
2017-03-23
The following formula can be used to calculate the maximum cable lengths.
Operating voltage
Permissible voltage
drop per line
Formula for cable
length
AC 24 V
4 % of AC 24 V
L =
P
A
1313
∂
Ζ
m
∴
A Cross-sectional area in [mm
2
]
L Permissible cable length in [m]
P Power consumption in [VA] or [W];
refer to the actuator’s type field
Operating
voltage
Power
consumption
Perm. voltage drop for line...
1 (G), 2 (G0)
AC 24 V
3 VA
4 % of AC 24 V
Determine the cable lengths for 4 actuators operating on AC 24 V. Decisive for
sizing the cable are only the AC currents on lines 1 (G) and 2 (G0). Maximum
permissible voltage drop =
4 % per line
.
∂
Consumption = 4 x 3 VA = 12 VA
∂
Line current = 4 x 0.125 A = 0.5 A
Permissible single cable length for G and G0:
∂
164 m with a cross-sectional area of 1.5 mm
2
∂
274 m with a cross-sectional area of 2.5 mm
2
4.2.2 Bus
cabling
Instructions regarding topology and addressing in KNX networks can be found in
the documents [13] and [16]. The following sections presuppose electrical
installations that conform to the KNX-TP1 standard
Formula for cable
length
Example:
Power
consumption and
permissible voltage drop
(1 VAV controller)
Example:
Parallel
connection of
4 actuators
