A megger is an instrument used for measuring

Megger:

• Megger is a portable instrument to measure high insulation resistances. 
• It 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 hand-driven generator (permanent magnet D.C. generator).
• The operation of a megger is based on 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.