Which of the following is a common cause of conductor insulation failure?

Excessive voltage stress is indeed a common cause of conductor insulation failure. When conductors are subjected to voltages that exceed their rated capacity, the insulating material can degrade over time or even fail suddenly. This happens because the insulating material is designed to withstand certain voltage levels; exceeding these levels can lead to electrical breakdown, where the insulation can no longer effectively prevent electrical current from leaking out of the conductor. This can result in arcing, short circuits, or even fire hazards.

In contrast, while overcurrent conditions can lead to heating of conductors and potential damage, the insulation may still hold up unless the temperatures become extreme. Short circuits often create a rapid surge of current that could damage equipment, but the primary failure mode in such cases is typically related to overheating rather than direct insulation failure. Device failure can occur for various reasons, including mechanical or thermal losses, but it is not as directly related to the insulation integrity of a conductor as excessive voltage stress.