Manual Datafox ZK-MasterIV
3.6.2.3 Topologie
If a bus topology is used when setting up the network, you have to calculate the cable cross-section for each
bus segment with regard to the maximum power consumption of the respective segment (see figure
).
At a star cabling the cable cross-section for each cable has to be calculated with regard to of the power
consumption of the respective module.
Note:
Because this document only deals with the voltage supply of an access control
system, the depiction of the RS485 data bus is abandoned in the figures. The
voltage supply is simply depicted as one line. Additionally, the cable length that
has to be calculated is marked by a broken line.
3.6.2.4 Examples
3.6.2.4.1 Bus topology
We take as a basis that the longest distance from the voltage source to the last module is 65 m.
Figure 53: Bus topology
In order to assure a high safeguarding and to keep the calculation simple, you can take the following
steps. Calculate the power consumption of all modules connected to a voltage source (max. 16 modules)
and take the longest distance from the voltage source to the last module. If the result of this simplified
method of calculation for the cable cross-section is a value higher than
1
,
5
mm
2
, you have to use ad-
ditional power supply units and recalculate the system. By this additional power supply unit you can
compensate the voltage drop at a smaller cable cross-section by a shorter cable length (two sub-networks
with regard to the voltage supply not with regard to the RS485 data bus). The calculation of the total
power consumption for the example in figure
is as follows.
I
4
56
,
5
mA
2
156
,
0
mA
5
180
,
0
mA
1
.
438
mA
1
,
438
A
Now we put the values in the equation and get the necessary cable cross-section:
Version: 04.01.07.00
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