Which of the following factors can lead to insulation failure?

The correct choice highlights key factors that can lead to insulation failure, encompassing a broad range of influences on insulation performance. Overvoltage can cause dielectric breakdown in the insulating material, resulting in short circuits or other electrical failures. Mechanical stress might lead to physical damage or the development of micro-cracks in insulation, which can compromise its integrity. Thermal degradation occurs when insulation materials are subjected to excessive heat, leading to material breakdown and loss of insulating properties. Exposure to chemicals can also deteriorate insulation materials, especially in industrial environments where exposure to hazardous substances is common.

This comprehensive view shows how various physical and environmental factors interplay in contributing to insulation failure, making the correct answer comprehensive and reflective of real-world conditions in electrical systems. Other options, while they address relevant scenarios, do not capture the full range of factors that influence insulation failure.