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EARTHING + LIGHTNING PROTECTION
T
he components used for installing the external lightning protec-
tion system shall meet the mechanical and electrical require-
ments which are specified in the SANS/ IEC 62561 [2] series.
The lightning protection components are categorised according to
their function as follows:
All metallic lightning protection components (clamps, conductors,
air-termination rods, earth electrodes) exposed to weathering must
be subjected to artificial ageing prior to testing. This is to verify the
components` suitability for its intended function.
Lightning protection components are subject to natural weather-
ing and exposure to corrosion; it is therefore necessary to artificially
age the components before conducting other mechanical strength
and electrical property tests.
Testing of Lightning Protection System components
Artificial ageing
Artificial ageing takes place in two steps:
Step one: Salt mist treatment
This test is intended for components or devices which are designed to
withstand exposure to a saline atmosphere. The tests are conducted
in a salt mist chamber where the specimens are tested with a test
level 2 for more than three days. Test level 2 includes three spraying
stages using a 5% sodium chloride (NaCl) solution at a temperature
between 15°C and 35°C followed by a humidity storage at a relative
humidity of 93% and a temperature of 40°C for 20 to 22 hours.
Step 2 : Humid sulphurous atmosphere treatment
This test is used to evaluate the resistance of materials and com-
ponents to condensed humidity containing sulphur dioxide. The
specimens are placed inside a test chamber where they are treated
with a concentration of sulphur dioxide for seven cycles. Each cycle
has a duration of 24 hours consisting of sulphur dioxide treatment
for eight hours followed by a rest period of 16 hours. Thereafter, the
sulphurous atmosphere is replaced. Only components for outdoor
use and components that are buried in the ground are subjected to
ageing or conditioning before testing. Buried components have ad-
ditional requirements and measures that must be considered, e.g.
No aluminium clamps or conductors may be buried in the ground.
Components for indoor use such as equipotential earth bars do not
have to be subjected to ageing or conditioning. The same applies to
components which are embedded in concrete. These components
are often made of non-galvanised steel.
Air termination systems, masts, rods
The size and dimensions of air termination masts and conductors
vary significantly between different structures and different designs,
for example, 2 m or 3 m long masts may be installed on flat roofs
and 25 m telescopic lightning protection masts may be installed in
explosive areas. SANS / IEC 62561-2 [2] specifies the minimum cross
sections and allowable materials with the corresponding electrical
and mechanical features for each type of air termination mast. For
longer air termination masts, the bending resistance of the air ter-
mination mast and of the stability of the complete air termination
system has to be provided for by means of a static calculation. The
required cross sections and materials must be selected based upon
these stress calculations. Wind speeds and wind loads also have to
be taken into account.
Connection components
The connection components are simply called ‘clamps’ and the
clamps are used to connect various parts of the lightning protection
system together (down conductor to air termination system etc).
There are therefore many different clamp combinations that are
possible. In the case of lightning current loading, clamps are subject
to electrodynamic and thermal testing, which highly depend on the
type of conductor and the clamping connection. The clamps also
allow for the connection of different types of conductors, these dif-
ferent materials all have differing mechanical strengths and thermal
properties. This is particularly evident for stainless steel connection
components, where due to the low conductivity, high temperatures
Test combinations
for MV clamps.
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October ‘15
Electricity+Control