Answer / hariprasanna

megger is used to measure insulation resistance (mohm)of let transformer ..so to do this we have to connect it to the body of transformer and windings ,so if we use ac then there will be probability of dielectric change and discharge,so we use dc in megger to get a constant supply...but in earth tester it is uesd to measure earth resistance ,if we use dc hear then as nwe know earth contain metals,chemicals..so due to electrolysis corrosion will start around earth electrode..so to aviod this we use ac ..

Answer / anindya chitta bagchi

true,earth tester generates ac voltage.

Answer / rajesh tokalapudi

As per my knowlegde there is no much diffrence between
megger and earth megger.megger is used to measure
insulation resisitance(mega ohm)and earth megger is used to
measure earth resistance(ohms).constructionally there is no
difference.both contains an in built permanant magnet hand
driven generator.The difference lies in the no of
terminals.megger contains 3 and earth megger contains 4
terminals.Both will generate dc voltage only during
measurement.

Answer / avinash

Megger and Earth tester have opposite functions. Megger check insulation resistance to make sure there is no path to Earth, and it measure the resistance in Mega ohms. Megger uses DC to avoid conductance due to reactive components.

Earth tester function makes sure there is very good path to Earth and measures resistance in fraction of ohms. It uses AC to make sure there is no inductance in path. With DC inductance can give false zero reading.

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