Connection
5.7 Effect of cable length on the supply voltage
SIMATIC RF185C, RF186C, RF188C, RF186CI, RF188CI
46 Operating Instructions, 04/2020, C79000-G8976-C512-03
5.7 Effect of cable length on the supply voltage
When wiring your assembly, you need to take into account the effect of the cable length on
the supply voltage of the communication module.
The following figure shows the voltage drop as a function of the cable length for 2, 4, 8 and
16 amperes, using the example of a copper cable with ∅ 1.5 mm
2
. A simple copper line is
used as an example. Depending on the design, the power supply line and the ground line
must be taken into account.
Figure 5-13 Voltage drop with copper cables with a cross-section of 1.5 mm
2
To estimate the voltage drop in your communication module, you must add the voltage drops
of the cables.
Example
With 16 A the voltage drop via the two L-coded M12 plug-in connectors and in the
communication module is approximately 0.2 V. The value can vary significantly depending
on the plug connection or condition.
When using a 7 m power cable with ∅ 1.5 mm
2
, the voltage drop is approx. 2.6 V with a 16 A
load.
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