FAQ

15.Expected Cable life
Many environmental and operational conditions can influence the longevity of electrical cables in service.
The materials of insulation and sheathing may be degraded when exposed to heat, chemicals, UV, ozone, excessive flexing, mechanical tension, or attack by termites and rodents.  
When a current passes through the conductor of cable, heat occurs. If the conductor kept at high temperature which near or exceed it can bear for a long time, it will results an big problem. The insulation and sheath would be damaged and the whole cable needs to be replaced.
In spite of factor of the insulation and sheathing materials, water immersing and poor fixings can also cause corrosion and damage to cable.