Page 302 - 35_DS702_E_2014_Lightning_Protection_Guide

CCTV systems are used in all sectors for access control and cable. Coaxial cables are used for unbalanced transmission, in
facility supervision. In the following, surge protection meas- other words the video signal is transmitted through the core
ures will be described which meet the high availability require- of the coaxial cable (inner conductor). The shield (earth) is the
ments of CCTV systems. reference point for signal transmission. Balanced transmission
A CCTV system consists of at least one camera, one monitor (baluns) where the coaxial signal is converted to a two-wire
and one suitable video transmission path. Remotely controlled
camera stations are typically equipped with a pan / tilt head signal is used for two-wire cables.
which allows the operator to individually adjust the position The voltage supply cable is often routed separately. In case of
and the perspective of the station. IP cameras, however, a single cable is used for the transmis-
In the simplest case, the transmission line between the junc- sion of the video signal and for voltage supply. An RS 485 bus
tion box and the monitor is a coaxial or a balanced two-wire controls the panning and tilting of the camera.

air-termination rod camera monitor control
camera board
pan / tilt head

junction box

pan / tilt head
short coaxial or
steel mast two-wire cable

junction box
230 V cable RS 485 cable
MEB

Figure 9.7.1 Camera connected to a building with external lightning protection system and lightning current carrying surge protective devices
on both ends

camera camera monitor control
board
pan / tilt head

pan / tilt head junction box

coaxial or
two-wire cable

junction box

230 V cable RS 485 cable

Figure 9.7.2 Camera connected to a building without external lightning protection system with surge protective devices on both ends

www.dehn-international.com LIGHTNING PROTECTION GUIDE 301