How significant is insulation resistance testing? Since 80% of electrical maintenance and testing involves evaluating insulation integrity, the answer is "very important." Electrical insulation starts to age as soon as it's made. And, aging deteriorates its performance. Harsh installation environments, especially those with temperature extremes and/or chemical contamination, cause further deterioration. As a result, personnel safety and power reliability can suffer. Obviously, it's important to identify this deterioration as quickly as possible so you can take the necessary corrective measures.