A lightning arrestor is designed to protect WLAN devices from static
electricity and lightning surges. It is similar in function to a safety valve
on a steam boiler. A lightning arrestor prevents energy surges from reaching
the equipment by shunting the current to the ground. A lightning arrestor is
shown in Figures
and
.
A
lightning arrestor has two main purposes:
- To bleed off any high static charges that collect on the antenna, which
helps prevent the antenna from attracting a lightning hit
- To lessen or dissipate any energy that gets induced into the antenna or
coax, which comes from a near lightning strike
The most important part of installing a lightning arrestor is to
install a proper earth ground, which will dissipate excess energy. This is
typically done using a grounding rod. A grounding rod is a metal shaft driven
into the ground, usually to a depth of at least 2.44 m (8 ft). Grounding rods
can be made of iron or non-iron materials. When a grounding rod is made of iron
or steel, which are ferrous materials, it needs to be at least 15.9 mm (0.63
in.) thick. Non-ferrous rods must be free of all non-conductive materials
including paint. It must be greater than 12.7 mm (0.5 in.) thick.
Electricity will follow the path with the least resistance to get to the
ground. Most codes call for a ground system of 25 ohms or less. A clamp type
meter can be used to measure the resistance of grounding rods. If a single
electrode does not meet the grounding requirements, additional electrodes can
be added. If multiple electrodes are installed to meet these requirements, they
should be at least 1.83 m (6 ft) apart.