Section 3
Installation
18
FT702LT Flat Front Wind Sensor Manual
3.3.2
Protection Against Indirect Lightning Effects and Electromagnetic Interference
Objects within the protection zone described above can still be subject to very high electromagnetic field and
partial lightning surge currents. It is therefore critical that appropriate shielding and termination is used
throughout the system to reduce these effects. A shielded signal cable will offer some protection however it is
recommended that double shielding is employed between the sensor and the chassis of the computer and
power supply cabinet.
A metal conduit surrounding the shielded cable is a good way of providing this additional protection and will also
help to prolong the life of cables and connectors. The impedance of the metal conduit needs to be as low as
possible since a substantial proportion of the lightning current will flow in it. An example of metal conduit could
be
‘s HelaGuard steel conduit with plastic coating and steel
overbraid.
All cable shielding must be continuous and terminated at both ends using EMC glands or cable clamps with a
direct connection to the cabinet chassis. There must also be a direct connection from the cabinet chassis to the
grounding reference. Any metal conduit used must also be continuous and terminated at both ends with
appropriate fittings. Figure 13 below shows the principle of the protection scheme.
①
Preferably this
connection is established
using structural steel
parts or alternatively by
use of a copper cable
with a cross section of
min. 50mm
2
②
Any shielding conduit
must be terminated at
both ends
③
Shielded cable must
either be terminated
using an EMC cable
gland in the cabinet wall -
or alternatively using a
cable clamp in direct
connection with the
cabinet chassis
④
The chassis of the
cabinet must have a
direct connection to
ground
Figure 13: Protection of equipment against indirect effects
