Thank you for Visiting the Mitchell Instrument Company Megohmmeter/Insulation Resistance Tester Store!
Mitchell Instruments has been a premier distributor of Megohmmeters (also called Insulation Resistance Testers) for over 30 years! We carry and usually keep in stock all the top brands like Megger, AEMC, Fluke, Hioki, Extech and many more. We try to always offer the best price you will find and are 100% committed to customer satisfaction.
Insulation resistance testers can be used to determine the integrity of windings or cables in motors, transformers, switchgear, and electrical installations. The test method is determined by the type of equipment being tested and the reason for testing. For instance, when testing electrical cabling or switchgear (low-capacitance equipment) the time-dependent capacitive leakage and absorption leakage currents become insignificant and decrease to zero almost instantly. A steady conductive leakage current flow is reached almost instantly (a minute or less) providing perfect conditions for the spot-reading/shorttime resistance test.
Figure 1-36.—A megger internal circuit.Coil a is connected in series with R3 and the unknown resistance, Rx, to be measured. The combination of coil, R3, and Rx forms a direct series path between the positive (+) and negative (-) brushes of the dc generator. Coil b is connected in series with R2 and this comination is also connected across the generator. There are no restraining springs on the movable member of the instrument portion of the megger. Therefore, when the generator is not operated, the pointer floats freely and may come to rest at any position on the scale.
The most important reason for testing insulation is to insure public and personal safety. By performing a high dc voltage test between de-energized current- carrying (hot), grounded, and grounding conductors, you can eliminate the possibility of having a life-threatening short circuit or short to ground. This test is usually performed after the initial installation of the equipment. This process will protect the system against miswired and defective equipment, and it will insure a high quality installation, customer satisfaction, and protect against fire or shock. The second most important reason for insulation testing is to protect and prolong the life of electrical systems and motors. Over the years, electrical systems are exposed to environmental factors such as dirt, grease, temperature, stress, and vibration. These conditions can lead to insulation failure, resulting in loss of production or even fires. Periodic maintenance tests can provide valuable information about the state of deterioration and will help in predicting possible failure of the system. Correcting problems will result not only in a trouble-free system, but will also extend the operating life for a variety of equipment.