4.2　The Types of Earthing and Bonding

4.2.1　The types of earthing and bonding at the comprehensive telecommunication building may be classified into the bonding system of external ring main earthing conductor and the bonding system of vertical riser.

4.2.2　The bonding system of external ring main earthing conductors may be designed according to Fig.4.2.2.The bonding system of external ring main earthing conductors may be applied to the comprehensive telecommunication building with low height and large area or with rectangular shape，or used for several floors or some equipment rooms of the high-rise comprehensive telecommunication building，or adopted by bureaus（stations）having high risk of electromagnetic pulse.The bonding system of external ring main earthing conductors shall be in accordance with the following requirements：

1　For facilities at each floor or equipment rooms at corresponding floors，the ring main earthing conductors shall be installed by one circle around the interior of buildings；the ring main earthing conductor shall be connected with the preinstalled earth terminal for rebars of building pillars；the height of ring main earthing conductors shall be selected according to the condition of equipment rooms.

2　Vertical bonding conductors shall be connected with ring main earthing conductors at each floor or equipment rooms at corresponding floors.The quantity and spacing of vertical bonding conductors shall be in accordance with the following requirements：

1）At each corner of buildings，there shall be at least one vertical bonding conductor；

2）When the space between conductors at corners and those at the middle of buildings exceeds 30m，additional vertical bonding conductors shall be installed，and the spacing of vertical bonding conductors should be laid uniformly.

3　The ring main earthing conductor at the first floor shall be connected with the external ring earth electrode once at an interval of 5m-10m，and following objects shall be connected to the ring main earthing conductor：

1）Earthing bars in each cable entrance facility；

2）The collection points of shielding layers of power cables and various earthing conductors；

3）Various pipeline systems in structures；

4）Other metal conductors entering buildings.

4　Branched ring main earthing conductors may be added in corresponding equipment rooms，which shall be connected with the ring main earthing conductors.

5　In large-size telecommunication buildings，the scope of ring main earthing conductors for the earthing system may be shrunk to the building areas where there are telecommunication equipment equipment rooms，and the scope and the quantity of vertical bonding conductors should be set according to the actual situation.

6　One voltage balancing net shall be disposed every other floor in large-size telecommunication buildings.

4.2.3　The bonding system of vertical riser shall be designed according to Fig.4.2.3，which shall be in accordance with the following requirements：

1　The main earthing terminal should be designed near the led-in point of AC mains power supply，and shall be connected with following parts：

1）Earthing connection of the earth grid；

2）Bonding conductors of the cable entrance facility；

3）Bonding conductors of the shielding layers of the AC mains power and various earthing conductors；

4）Bonding conductors of water pipe systems in structures；

5）Bonding conductors for other metal pipelines and buried structures；

6）Steel structures of buildings；

7）One or more vertical risers.

2　For one or more vertical risers from main earthing terminals to each floor of buildings，the steel structure of buildings may be used as the vertical riser under the condition of electrical connection.

3　Each vertical riser shall serve the telecommunication equipment located within a area of a 30m（long side）rectangle centered on the vertical riser.Equipment outside this area should be served by other vertical riser.

4　Vertical riser shall be interconnected at an interval of two or three floors.

5　One or more floor earthing bar（s）shall be built at each floor.Each floor earthing bar shall be connected to the nearby vertical riser，and each floor earthing bar shall be arranged at the center of place where the earthing of telecommunication equipment is to be provided for each subtelecommunication system.

6　Various equipment bonding network，the earthing conductors of direct current electric units and other systems shall be connected to the earthing bar on their floor.

4.2.4　Telecommunication equipment，very sensitive to thunder and lightning，shall be far away from main earthing bar，cable entrance facilities，AC mains supply and connecting wires among earthing systems.