●建筑物内的导线使用年久失修，其绝缘层老化破损。
The conductors in buildings are out of repair for a long time, and their insulation layer is aging and damaged.
●建筑物内导线安装施工不规范，如导线不穿阻燃管，直接埋于墙内或置于桁架上。
Installation and construction of conductors in buildings are not standardized, such as conductors without flame retardant tubes, directly buried in walls or placed on trusses.
●导线施工质量粗糙，偷工减料，使用钢管穿线时钢管内壁刮伤导线绝缘层。
Conductor construction quality is rough, Jerry work and material reduction. When using steel pipe to thread, the inner wall of steel pipe scratches the insulating layer of conductor.
●娱乐场所等公共活动场所在进行二次装修时，乱敷电线，致使各种施工遗留缺隐贴近易燃物；
During the second decoration of public places of activity such as entertainment places, wiring is laid indiscriminately, resulting in various kinds of construction remains close to flammable materials.
●电气设计不当，包括使用者随意增加负荷，造成导线过负荷而发热，导线绝缘层老化失效。
Improper electrical design, including user's arbitrary increase of load, resulting in overload and heating of conductors, aging and failure of insulating layer of conductors.
●用户内部私拉乱扯线路，架设极不规范。
Private pulling of lines within users is extremely irregular.
●线路受自然条件影响，如导线碰树，大风吹断导线，空气潮湿导致导线绝缘水平下降等。
Circuits are affected by natural conditions, such as wire hitting trees, wind breaking conductors, air humidity leading to the decline of conductor insulation level, etc.
●各种人为的破坏造成断线等。
Various kinds of man-made destruction caused wire breakage and so on.