Introduction:
The buildings and structures shall be protected from lightning strikes by installing well designed and executed lightning protection system (LPS). An External LPS provides protection against physical damage and life hazards whereas internal LPS provide protection for electrical and electronic systems.
The following methods are specified by IEC 62305 - 3 to determine the position of air termination system.
1) Protection Angle Method
2) Rolling Sphere Method and
3) Mesh Method
In mesh method, the mesh size depends on the level of protection.
The following conditions should be fulfilled for protecting a structure by using Mesh Method:
1) Air termination conductors are positioned on
- Roof edge lines,
- Roof overhangs,
- Roof ridge lines having slope < 1/10.
2) The mesh dimensions should not be greater than the values specified by IS/IEC 62305 part 3.
3) The lightning current should have at least two distinct metal routes to earth termination.
4) Any structures protruding from the surface outside the volume won't be protected by this,method.
5) The route should be the shortest and most direct route.
If the structure to be protected has different roof levels, we have to install mesh of suitable size on all the roof levels and the mesh of different roofs should be interconnected. An Example of mesh protection system for flat roof structure is as follows.
For buildings with some items protruding from the flat surface, PAM is commonly used along with the mesh method. The protection provided by the air termination rod can be calculated as explained in Article 1.13 as per IS/IEC 62305. The example for such condition is as follows:
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