WORKS on the principle of ELECTROMAGNETIC induction.The electrical power to a megger is provided by a permanent magnet D.C. GENERATOR.The test voltages are usually of order 500, 1000, or 2500 V are generated by a hand-driven generator (permanent magnet D.C. generator).The operation of a megger is based on a moving COIL meter.EARTH pit resistance is measured with an earth tester, also called earth megger which can test the resistance across a range of currents and distances.Insulation megger is used to measure the insulation resistance of the cables. Examples of High Resistance Materials:Cable Insulation Resistance.All Motors, generators, and transformers winding's insulation resistance.All semiconductor devices when reverse biased. Methods to measure High Resistance:Loss of charge method.Direct-Deflection method.Mega ohm Bridge.Megger.