Specifications

Lighting Protection in the form of diode and gas tube lighting suppressors
need to be installed at one end and maybe both ends of any long cable run. The
long cable runs are more prone to voltage build ups due to local lightning static
discharges.
When lightning strikes from cloud to cloud or from the upper atmosphere to
the ground, a differential charge appears on the ground. Since the charge is not
equal at all points on the ground, this differential change will cause current the
flow down any conductor connected to both grounds. This current flow can be
thousands of amperes occurring for only milliseconds, but in that short amount of
time the current causes a sharp rise in the voltage that can reach thousands of
volts. Your CCTV equipment is not designed to withstand that kind of voltage at
the video input and output terminals, so the equipment gets permanently
damaged.
For safety sake you should install lightning protection on your video cables
but be sure to BOND EVERY LIGHTNING PROTECTION DEVICE with the
LEAST POSSIBLE
INDUCTANCE TO MINIMISE THE AMOUNT OF VOLTAGE
THAT WILL BE DEVELOPED BETWEEN THEM WHEN THE LIGHTNING DOES
STRIKE. Even a few inches of #l6 wire is enough to generate up to 300 volts or
more at the video input frying the video system when lightning strikes, (not
because of the resistance of the wire but because of the inductance of the wire
connecting the lightning protection unit to the ground).
A lightning strike is a very short duration event, and so the signal it creates
has very high frequency content, this is why the inductance of the connecting
wires, not the resistance determines the effectiveness of the lightning protection
device.
Even a very small inductance on the order of one or more nano-Henrys is
capable of generating very high voltages between the video equipment and the
lightning protection devices during a lightning discharge. The ground wires on the
lightning protection devices should be as short as possible. Do not add extra wire
to the ground wire to extend the connection, instead route the video cable over to
the lightning protection device mounted as close to the ground as you can so that
the ground path for the current will be as short as possible.
There is one more thing to consider when using lightning protection.
Lightning protection requires a good ground to function. That ground can induce
ground loop artifacts into your video signal. Now that you have protected your
video equipment with the lightning arrestors, you may discover that you now have
a ground loop in your video image.
CCTV TRAINING MANUAL PAGE 15 OF 28