Electrical Cable Insulation Resistance Test

A common rule of thumb is insulation resistance changes by a factor of two for each 10 degrc change.

Electrical cable insulation resistance test.

As a production test this test is often used as a customer acceptance test with minimum insulation resistance per unit length often specified by the customer. For low voltage installations i e. The ohmmic value of the insulation resistance is expressed in megohms mω. 230v to measure insulation resistance in ohm s.

If no literature from the manufacturer is available apply 500 volts dc for 300 volt rated cable and 1000 volts dc for 600 volt rated cable. Megger mit1020 10 kv insulation resistance testers are all designed specifically to assist the user with the testing and maintenance of high voltage equipment. The measurement of insulation resistance is a common routine test performed on all types of electrical wires and cables. The measurement of insulation resistance is a common routine test performed on all types of electrical wires and cables.

The measured resistance has to be higher than the indicated limit from the international standards. Performing time resistance tests on large switchgear transformers bushings motors and cables especially at higher voltages require high insulation resistance ranges and clean consistent test voltages. The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator. This is a simple nondestructive method of determining the condition of the cable insulation to check for contamination due to moisture dirt or carbonization.

The insulation resistance test is the second test required by the electrical safety testing standards. For good insulation the resistance usually reads in the megohm range. Insulation resistance test. What is insulation resistance testing.

The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. The measured resistance indicates the condition of the insulation between two conductive parts. When temperature increases insulation resistance decreases and vice versa. Test period must be for 1 minute using a voltage according to manufacturer s published data.

Its objective is to measure the ohmmic value of the insulation under a direct voltage of great stability generally 50 100 250 500 or 1000 vdc. Perform an insulation resistance test on each conductor with respect to ground and adjacent conductors. The insulation resistance of cable is measured using a megohmmeter. Good insulation shows this charge effect over a time period much longer than the time required to charge the capacitance of the insulation.

Sample insulation resistance megohmeter test connections for cable and transformer using guard terminal. Insulation resistance is temperature sensitive.