Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 230

Appendix
A.3 Lightning and surge voltage protection
Scheme of the lightning protection zones of a building
The figure below shows a block diagram of the lightning protection zone concept for a
detached building.
External
lightning
protection
Power
cable
Principle of the transition points between lightning protection zones
At the transitions points between lightning protection zones, you must take measures to
prevent surges being conducted downstream.
The principle of the lightning protection zone concept also specifies that all cables which are
capable of carrying lightning current (!) and installed at the transition points of lightning
protection zones must be included in the equipotential bonding.
Conductors and cables capable of carrying lightning current are:
• Metal pipes (e.g. water, gas and heat)
• Power cables (for example, mains voltage, 24 V supply)
• Data cables (for example, bus cable).
A-20
Lightning protection zone 0 (field side)
Lightning protection zone 1
Lightning protection
zone 2
Lightning
protection
zone 3
device
Metal
part
Data cable
Building shielding
(steel armor)
Room shielding
(steel armor)
Device shielding
(metal housing)
Nonelectrical
cable (metallic)
Internal
cable
Lightning protection
equipotential bonding
Local equipotential
bonding
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05