Metallic Roofing:
LPS conductors and rods should be able to withstand the stress due to wind and other weather conditions. Metal covering of outer parapet walls may be used as a natural component of the air - termination, if there is no risk of fire due to melting of metal. The conductors should be able to withstand the partial lightning impulse current flowing through them.
The metallic roof may be perforated by a lightning flash at the striking point. As a result, water will leak through the roof. If water leaking is not acceptable then a separate air-termination system should be installed.
Roof made of conductive sheets should meet the minimum thickness requirements as specified by IS/IEC 62305 part 3.
Flush-mounted and protruding structures on the roof surface should be protected by means of air-termination rods.
Natural Coponents:
1. The metal in the reinforced concrete of the structure:
The electrical continuity of the rod should be ensured and the interconnections should be proper.
In the case of pre-stressed concrete, the mechanical stress due to the passage of lightning current through the metals also has to be considered.
2.The interconnected steel framework of the structure;
If the interconnected reinforcing steel framework is used as down conductors. then ring conductors are not necessary.
Let us consider a residential building, which utilises the natural components (reinforcement bars) of the building as down conductor with external ring earthing being installed below the ground level. For this condition, the down conductors should be connected to reinforcement bars near the roof of the building and the connections to external ring earth electrodes are taken from the reinforcement bars at a height of 1.5m above the ground level.
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