All cable insulation deteriorates naturally with age, especially when exposed to elevated temperature due to high loading and even when it is not physically damaged. The result is a distributed flow of current leakage. An interruption of power service may result. Many substances such as water, salt, oil and chemicals can contaminate and shorten the life of insulation and cause serious problems. Some types of insulation are subject to a condition termed 'treeing'. It has been found that the
presence of moisture containing contaminants, irregular surfaces or protrusions into the insulation plus
electrical stress provides the proper environment for inception and growth of these trees within the insulation material. Testing
indicates that the AC breakdown strength of these treed cables
is dramatically reduced. Damage caused by lightning, fire, or overheating may require replacement
of the cable to restore service.