Siemens S5-100U User Manual page 69

Installation Guidelines
Protection against Lightning
If you run cables and lines for SIMATIC S5 devices outside buildings, you must use shielded cables.
The shield must be able to conduct current and be connected at both ends to ground. Use double-
shielded cables for analog signal lines. Ground the inner shield on one end only.
In addition, you must connect signal cables to protective elements, such as varistors or lightning
arresters filled with inert gas, so that you don't have an overvoltage. The protective elements should
be present where the cable enters the building, if possible. Otherwise, the protective elements
should be where the cable enters the cabinet.
SIMATIC cabinet
Figure 3-28. Layout of Elements to Protect against Lightning
Note
Use varistors or lightning arresters filled with inert gas to protect against overvoltages.
Install these protective elements where the cable enters the building, if possible.
Each system must be looked at individually to determine measures that should be taken
to protect it against lightning. Please address your questions to your local Siemens
office.
EWA 4NEB 812 6120-02
PLC
Lightning
arrester
Varistor
S5-100U
Sensors/
actuators
3-37