Basic Documentation

18 / 42
Siemens VAV Compact Controller Modbus RTU A6V10631862_en--_e
Smart Infrastructure 2021-10-26
The following formula can be used to calculate the maximum cable lengths.
Operating Voltage
Permissible voltage drop
Formula for cable length
AC 24 V
4 % of AC 24 V
L =
P
A1313 •
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 Modbus RTU networks can be
found in [7]. The following sections presuppose electrical installations that conform
to the protocol-specific requirements.
Formula for cable
length
Example: Power
consumption and
permissible voltage drop
(1 VAV controller)
Example: Parallel
connection of
4 actuators