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What is insulation resistance testing?

insulation resistance testing

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. When you're applying a voltage (specifically a highly regulated, stabilized DC voltage) across a dielectric, measuring the amount of current flowing through that dielectric, and then calculating (using Ohm's Law) a resistance measurement. The resistance measurement is in megohms. You use this resistance measurement to evaluate insulation integrity.

What's the purpose of insulation resistance testing?

You can use it as:

  • A quality control measure at the time a piece of electrical equipment is produced;
  • An installation requirement to help ensure specifications are met and to verify proper hookup;
  • A periodic preventive maintenance task; and
  • A troubleshooting tool.

How do you perform an insulation resistance test?

Generally, you connect two leads (positive and negative) across an insulation barrier. A third lead connects to a guard terminal. This guard terminal allows you to be selective in evaluating certain specific components in larger pieces of electrical equipment. After you make your connections, you apply the test voltage for 1 min. (This is a standard industry parameter that allows you to make relatively accurate comparisons of readings from past tests done by other technicians.)

During this interval, the resistance reading should drop or remain relatively steady. After 1 min, you should read and record the resistance value. The International Electrical Testing Association (NETA) provides the values for the resistance of electrical power distribution equipment. When performing insulation resistance testing, you must maintain consistency. The same piece of equipment should be tested, the same way and under the same enviornmental parameters, each time. Megohmmeter testing is usually performed on every existing receptacle, switch and lighting fixture.


At Light It Up Electric, our trained New Jersey electricians have experience in insulation resistance testing. This advantage allows us to deliver real value to our clients with an unmatched quality. We always take pride in completing our jobs in a timely fashion and can all your electrical services under one roof.


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If you are in need of a New Jersey electrician for insulation resistance testing, please contact Light It Up Electric at 855-333-9354 or feel free to complete our online request form. Always keep in mind that we will beat any written estimate by 10%.