3.15　The Lightning Protection and Earthing of Optical Fiber Cable

3.15.1　During selection of routing of optical cable，following susceptible zones of lightning accidents shall be kept far away：

1　Where a sudden change occurs to the soil resistivity ρ10 at the depth of 10m.

2　The junction of rocky mountains and rice paddies or rivers，the boundary of mineral reserves，the boundary of mountain forests and geological fault zones.

3　An adret or windward slope facing to vast water surface.

4　Higher or isolated mountain top.

5　Places where lightning accidents occur frequently.

6　Isolated towers and bracing wires，towering buildings and other protective devices at the nearby.

3.15.2　Lightning protection measures shall be taken when optical cables may be laid at middle keraunic zones or above，or in areas with a history of lightning stroke.

3.15.3　Following measures may be taken for lightning protection of non-metallic line pairs and direct burial optical cables that have metal parts：

1　The setting of lightning protection lines shall be in accordance with the following requirements：

1）In areas where ρ10 is＜100Ω·m，lightning protection lines may not be set；

2）In areas where ρ10 is 100Ω·m-500Ω·m，one lightning protection line shall be set；

3）In areas where ρ10 is＞500Ω·m，two lightning protection lines shall be set；

4）The continuous laying length of lightning protection lines shall not be less than 2km.

2　When optical cables are laid in plastic pipelines in the open air for a long distance，the setting of lightning protection lines shall be in accordance with the following requirements：

1）In areas where ρ10 is＜100Ω·m，lightning protection lines may not be set；

2）In areas where ρ10 is ρ10≥100Ω·m，one lightning protection line shall be set；

3）The continuous laying length of lightning protection lines shall not be less than 2km.

3　Metal parts at two sides of the junction of optical cables shall not have electrical connection.

4　Metal parts of optical cables in the bureaus（stations）shall be earthed.

5　In areas of serious lightning accidents，optical cables may adopt the structure of non-metallic intensive cores or of non-metallic parts.

6　In areas susceptible to lightning stroke，cables in junction boxes of optical cables should be led in from two ends.

3.15.4　The route of optical cables shall be far away from isolated big trees，towers，towering buildings，street trees，woods and other susceptible lightning targets at serious lightning stroke areas.In case inevitable，protection measures such as arc suppression coils and lightning rods and the like shall be taken for the optical cable.

3.15.5　For the overhead optical cable，the provisions stipulated in item 3-5 of the clause 3.15.3 of this code shall be compiled with，furthermore，the following lightning protection measures may be taken：

1　Suspension wires of optical cables shall be earthed at intervals.

2　Overhead earth wires shall be set in areas where especially serious lightning accidents may occur.

3.15.6　The lightning protection of overhead optical cables in the bureaus shall be in accordance with the following requirements：

1　Overhead optical cable should be far away from special areas susceptible to direct lightning flash；suspension wires of optical cables shall be earthed by use of pole lightning conductors or bracing wires at an interval of 300m-500m，and insulators shall be added for electrical isolation at an interval of about 1km.

2　In areas where especially serious lightning accidents may occur，overhead earth wires shall be set above the overhead optical cables.

3.15.7　Direct burial optical cables and incoming low-voltage power cables of microwave stations and base stations at the bureaus or high mountains may be buried and laid in the same trenches or grooves.The burial depth should be determined according to geological conditions and the conditions that requirements on incoming low-voltage power cables are satisfied.