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Figure 5.8.6 shows the test set-up for testing the tensile Isolated air-termination systems
strength of round conductors (e.g. aluminium). The coating Isolated air-termination systems can be installed in a concrete
quality as well as the minimum thickness and adhesion to the base or tripod (without additional mechanical fixing). If air-
base material are important and must be tested particularly termination rods are between 2.5 m and 3.0 m high, they must
if coated materials such as galvanised steel (St/tZn) are used. be installed in a concrete base and mechanically fixed at the
Moreover, the conductor materials must be easy to process object to be protected using spacers made of insulating mate-
during the installation of lightning protection systems. Wires rial (insulating clearance made of GRP – glass-fibre reinforced
or strips, for example, are supposed to be easily straightened plastic) due to the wind load.
by means of a wire straightener (guide pulleys) or by means of If no additional measures are taken, high impulse voltages
twisting. These normative requirements are relevant product will cause flashover at the surfaces of the insulating materi-
features which must be documented. This information can be als. This effect is known as creeping flashover. If the creeping
found in the manufacturer’s product data sheets. discharge inception voltage is exceeded, a surface discharge
occurs which can easily flash over a distance of several metres
Earth electrodes and earth rods to earthed parts. This undesired flashover to metal installations
IEC 62561-2 (EN 62561-2) describes the requirements earth at or in the object to be protected can be prevented if the
electrodes have to fulfil. These requirements include the mate- necessary separation distance calculated in accordance with
rial, configuration, minimum dimensions as well as mechani- IEC 62305-3 (EN 62305-3) is maintained. In general, the sepa-
cal and electrical properties. The coupling joints linking the ration distance s is calculated as follows:
individual rods are weak points of earth rods. For this reason, k k
IEC 62561-2 (EN 62561-2) requires that additional mechanical s = i C l
and electrical tests be performed to test the quality of these k m
coupling joints. The test setup contains a test holder and a s Separation distance
steel plate (impact area). A specimen consisting of two joined k i Factor depending on the lightning protection level
rod parts with a length of 500 mm each is inserted into this selected
test holder. Three specimens are required for every type of k c Factor depending on the current distribution
earth electrode. The top end of the specimen is impacted with
a vibration hammer for a duration of two minutes. The stroke k m Factor depending on the material of the electrical
-1
rate of the hammer must be 2000 ± 1000 min and the single insulation
stroke impact energy must be 50 ± 10 [Nm]. l Length along the air-termination or down conductor
If the coupling joints have passed this test without visible de- from the point where the separation distance s is to
fects, they are subjected to artificial ageing consisting of a salt be determined to the nearest equipotential bonding
mist and humid sulphurous atmosphere treatment. After that, point or earthing point.
each coupling joint is loaded with three 50 kA and 100 kA It can be seen that the separation distance depends on the
lightning current impulses of 10/350 µs wave form. The contact length of the down conductor, the lightning protection level
resistance of stainless steel earth rods (measured above the selected, the distribution of the lightning current to the dif-
coupling) must not exceed 2.5 mΩ in case of stainless steel ferent down conductors and the insulating material in the in-
earth rods. sulating clearance. The factor k m must also be considered in
To test whether the coupling joint is still firmly connected af- addition to the factors k i , k c and the length l. The values of k m
ter being subjected to this lightning current load, the coupling have been sufficiently determined and proven for solid materi-
force is tested by means of a tensile testing machine. als and air.

Lightning protection components made of GRP DEHNiso spacers and DEHNiso Combi supporting tubes have
Nowadays roof-mounted structures such as domelights, anten- been sufficiently tested with impulse voltage and are specified
nas, air-conditioning systems, advertising signs, sirens, etc. are with a factor k m of 0.7 which is used to calculate the separa-
often located on the roofs of large office and industrial build- tion distance s. Thus, the factor k m of 0.7 can be taken into ac-
ings. These roof-mounted structures are typically electrically count when calculating the necessary separation distance for
operated or have a conductive connection into the building. the relevant object (air or solid material in conformity with the
According to the latest lightning protection technology, these standard). The separation distance calculated must be smaller
roof-mounted structures are protected against direct lightning or equal to the insulating clearance of the product used to pre-
strikes by means of isolated air-termination systems. This pre- vent flashover as shown in Figure 5.8.7 which would impair
vents partial lightning currents from entering the building. the function of the entire lightning protection system.

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