3.5　Main Earthing Conductor

3.5.1　Main earthing conductor should adopt the mode of ring main earthing conductor or earthing bar.The ring main earthing conductor should be installed at the basement，the first floor or the corresponding equipment rooms of buildings，or at the cabling racks for mobile communication or other small-size equipment rooms.The distance to the wall（cylinder）should be 50mm.The earthing bars may be installed in equipment rooms of different floors.When main earthing conductors are interconnected with earthing conductors via different metal materials，the electrochemical corrosion shall be avoided.

3.5.2　Copper bars with the sectional area not less than 90mm2 may be adopted for main earthing conductors，and those with the sectional area not less than 300mm2 shall be adopted for vertical risers at high-rise buildings.

3.5.3　Main earthing conductors may be installed at corresponding floors according to arrangement of telecommunication rooms and the conditions of buildings.