First, external damage. For example, the construction of unqualified cable laying and installation is easy to cause mechanical damage, and it is also easy to damage underground cables in civil construction. Sometimes, if the damage is not serious, it will take months or even years, which may lead to the complete breakdown of the damaged part, and sometimes it will seriously damage the electrical unit that may have a short circuit fault, which will directly affect the safety production. ?

The second is that the insulation is damp. For example, unqualified wire and cable connectors and connectors can make water or steam mix with water and trees in the stratum for a long time under the action of electric field in humid climate, and the insulation strength gradually causes cable damage. ?

Third, chemical corrosion. In the acid-base interaction area, it is often caused by armored cables, wires or corroded protective layers and outer protective layers, which will lead to poor insulation of protective layers and cable failure. ?

Fourth, long-term overload operation. During overload operation, due to the thermal effect of current and load current passing through the wire and cable, the conductor will inevitably heat up. At the same time, skin effect, eddy current charge loss and dielectric loss of steel armor will also generate additional heat, which will increase the temperature of the cable. ?

Five, cable connector failure. Wire and cable connector is the weakest link of cable connector failure, which leads to frequent and direct negligence. In the manufacturing method of cable joint, if the crimping is not tight and the heating is insufficient, the insulation of cable head will be reduced and accidents will be caused. ?