Exam Question
(a) Explain the working of a Megger with the aid of its internal circuit. (12)
(b) What safety measures are taken while using a Megger? (4)
Class 4 (4th Engineer)
MET
📅 Dec 2025
Reference Answer
### (a) Working of a Megger (Mega-ohmmeter)
#### 1. Principle of Operation
A Megger is a portable instrument used for measuring very high insulation resistances, typically in the range of Megaohms (MΩ). It operates on the principle of a ratiometer or electrodynamic moving coil instrument. The deflection of the pointer is determined by the ratio of the currents flowing through two sets of coils: a Current Coil (Deflecting Coil) and a Pressure Coil (Control Coil). This arrangement makes the reading independent of the exact magnitude of the test voltage, provided it is stable.
The final pointer position is an equilibrium point where the deflecting torque produced by the current flowing through the insulation under test is balanced by the controlling torque produced by the system's voltage.
#### 1. Principle of Operation
A Megger is a portable instrument used for measuring very high insulation resistances, typically in the range of Megaohms (MΩ). It operates on the principle of a ratiometer or electrodynamic moving coil instrument. The deflection of the pointer is determined by the ratio of the currents flowing through two sets of coils: a Current Coil (Deflecting Coil) and a Pressure Coil (Control Coil). This arrangement makes the reading independent of the exact magnitude of the test voltage, provided it is stable.
The final pointer position is an equilibrium point where the deflecting torque produced by the current flowing through the insulation under test is balanced by the controlling torque produced by the system's voltage.
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