Permissible cable lengths and cross-sectional areas
The permissible cable lengths and cross-sectional areas depend on the actuators’ current draw and the voltage drop on the connecting lines to the actuators. The necessary cable lengths can be determined from the following chart or with the help of the formulas. Cf. also to technical data in section 8.
When determining the cable length and the cross-sectional area, it is to ensure that the permissible tolerances of the actuators’ operating voltage are adhered to, in addition to the permissible voltage drop on the power supply and signal lines (see table below).
Permissible voltage drop
The cables are to be sized depending on the type of actuator used and based on the following data:
|Type||Operating Voltage||Line||Max. permissible voltage drop|
|GDB181.. / GLB181..||AC 24 V||G0, G||System voltage AC 24 V|
The power supply voltage drop at AC 24 V must not exceed 8 % (4 % over the G0).
L/P chart for AC 24 V
The chart below applies to AC 24 V operating voltage and shows the permissible cable length L as a function of power P, and the cross-sectional areas as a parameter.
Note on chart
The values in [VA, W] on the P-abscissa are allocated to the permissible voltage drops (ΔU/2U = 4 %) on line length L as per the above table and the basic diagram.
P is the decisive power consumption of all actuators connected in parallel.
Voltage drop on the
Formula for cable length
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 = [m]|
A Cross-sectional area in [mm2]
L Permissible cable length in [m]
P Power consumption in [VA] or [W];
refer to the actuator’s type field
Example: Power consumption and permissible voltage drop (1 VAV controller)
|Operating Voltage||Power consumption||Perm. voltage drop for line...
1 (G), 2 (G0)
|AC 24 V||3 VA||4 % of AC 24 V|
Example: Parallel connection of
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 mm2
274 m with a cross-sectional area of 2.5 mm2