第一，电缆制造缺陷，为非合格产品；

First, cable manufacturing defects, for non - qualified products;

第二，运行环境恶劣、自然老化、以及遭受外力破坏；

Second, the operating environment is bad, natural aging, and external force damage;

第三，安装不规范，接线粗糙。接地故障的根本原因却只有一个---电缆的绝缘材料。

Third, the installation is not standard, the connection is rough. The root cause of the grounding fault is only one - -- the insulation of the cable.