The components of Lightning Protection System (LPS) are exposed to direct lightning strikes and corrosive atmosphere. To achieve efficiency, the materials should have high current withstanding capacity and the materials should be less corrosive. The current carrying capacity of a material depends on the cross sectional area and the materials should be selected based on the local environment.
A material which is most preferable for some site conditions might be the least preferred material for other site conditions due to its chemical properties.
Apart from the corrosion of materials due to the local environment, the contact of two dissimilar materials also lead to galvanic corrosion.
Hence, IEC 62305 suggests the materials that can be used for different corrosive environments and it also given minimum cross sectional area for different materials of LPS Components.
Minimum Cross sectional area of different materials:
- Copper, tin plated copper strip, cable, Copper coated steel Should have minimum 50mm² cross-sectional area.
When mechanical strength not considered the cross sectional area of copper material can reduce up to 25mm²
- Minimum 176mm² cross sectional area should be considered for all materials of air terminals and 70mm² crosssectional area considered for sites where mechanical stress such as wind loading is not critical
- Normal cross sectional area of stainless strip, and conductor is 50 mm² and it can be increased upto 75 mm² when thermal & mechanical factors are considered.
Protection against corrosion:
- The LPS should be constructed of corrosion-resistant materials such as copper, aluminium , stainless steel and galvanized steel.
- The material of the airtermination rods and should be electrochemically compatible with the material of the connection elements and the mounting elements.
- Connections between different materials should be avoided.; otherwise they should be protected against galvanic corrosion.
- Copper parts should never be installed above galvanized or aluminium parts unless those parts are provided with protection against corrosion.
- Aluminium conductors should not be directly attached to calcareous building surfaces such as concrete, limestone and plaster, and should never be used in soil.
- Lead-sheathed steel conductors are not suitable for use as earth conductors
- Lead-sheathed copper conductors should not be used in concrete nor in soil with a high calcium content.
Aluminium has very good electrical conductivity but it more prone to corrosion on soil and concrete medium. Hence, they can be used for air terminal and down conductor systems above the ground level and connected to earthing system of GI/Copper/SS using proper bimetallic connectors. The fasteners or sleeves for aluminium conductors should be of similar metal and of adequate cross-section to avoid failure by adverse weather conditions.
