Lightning Protection System of Buildings

•The role of the building protection system is to protect it against direct lightning strokes. The system consists of:

–- the capture device: the lightning protection system;

–- down-conductors designed to convey the lightning current to earth;

–- "crow's foot" earth leads connected together;

–- links between all metallic frames (equipotential bonding) and the earth leads.

When the lightning current flows in a conductor, if potential differences appear between it and the frames connected to earth that are located in the vicinity, the latter can cause destructive flashovers.

Types of Lightning Protection System :

•Three types of lightning system protections are used in buildings. These are:

–The Simple Lightning Rod

–The Lightning Rod with Taut Wires

–The Lightning Conductor with Meshed Cage (Faraday cage)

The Simple Lightning Rod Protection System :

•The lightning rod is a metallic capture tip placed at the top of the building. It is earthed by one or more conductors (often copper strips) (see Fig. J-12).

                                    

                                                Fig. J-12: Simple lightning rod

The Lightning Rod with Taut Wires Protection System:

These wires are stretched above the structure to be protected. They are used to protect special structures: rocket launching areas, military applications and protection of high-voltage overhead lines (see Fig. J-13)

                                                           Fig. J-13: Taut wires

The Lightning Conductor with Meshed Cage (Faraday cage) :

•This protection involves placing numerous down conductors/tapes symmetrically all around the building. (see Fig. J-14)

•This type of lightning protection system is used for highly exposed buildings housing very sensitive installations such as computer rooms .

                                              Fig. J-14: Meshed cage (Faraday cage)