5.2　Tower Area

5.2.1　For steel tower that is individually installed or installed in concrete frame and the top of steel tower is higher than the frame，if its wall thickness is larger than or equal to 4mm，tower body shall be served as air terminal.

5.2.2　Vent pipe installed on the top of tower，vent pipe projected from the top side of tower，and any spaces beyond the pipe nozzle as specified in Article 5.11.2 of this Code shall be all located within the protection zone afforded by air terminal.

5.2.3　If tower body is used as air terminal，no fewer than two earthing points shall be provided and shall be equally spaced around tower body，and the spacing of down-conductors shall not be larger than 18m.Down-conductors shall be connected to the earthlugs provided on the metal base of tower body.If the nonmetal object or pipes connected to tower body is located beyond the protection zone provided for tower body，air terminal shall be installed at proper location for lightning protection.

5.2.4　Impulse earth resistance of each down-conductor shall not be larger than 10Ω.Earth-termination system should encircle the tower body to form a ring earth electrode.

5.2.5　For the concrete frame used to install tower body，the metal handrails on platform at each floor shall be interconnected to form a good electrical continuity path，and shall be connected to earthtermination system of tower body via down-conductor.Exposed metal conductor running along column or main longitudinal reinforcement in column with diameter not less than 10mm shall be served as downconductor.If the main longitudinal reinforcement in column are served as down-conductor，it shall be stirred up or welded，a steel sheet in size of 100mm×100mm shall be embedded on each end of column on each floor and used as the down-lead point for down-conductor，and the main longitudinal reinforcement shall be bonded to metal handrails or earth-termination system.