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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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What can be measured with the help of a Magger?
Winding continuity
Earth fault
Open circuit
All of this
All of this
Quick Summary: A Megger (Mega-Ohmmeter) is a portable instrument used to measure extremely high resistance values, typically the insulation resistance of electrical equipment. Because it generates high DC voltage internally, it effectively identifies insulation breakdown, winding continuity, and ground faults in cables, motors, and transformers.
A Megger (Mega-Ohmmeter) is a portable instrument used to measure extremely high resistance values, typically the insulation resistance of electrical equipment. Because it generates high DC voltage internally, it effectively identifies insulation breakdown, winding continuity, and ground faults in cables, motors, and transformers.
R=IV — Ohm's Law application where V is generated test voltage and I is the leakage current.
The Megger operates on the principle of a permanent magnet moving coil (PMMC) instrument combined with an internal hand-driven DC generator (or electronic equivalent). When the crank is turned, it generates a high DC voltage (V) across the test leads, producing a leakage current (I). The internal deflecting and controlling coils measure the ratio R=V/I, directly displaying the insulation resistance in Mega-ohms (MΩ).
Meggers typically use a voltage range of 500V, 1000V, or 2500V DC.
A zero reading indicates a short circuit (dead short to ground).
An infinity reading indicates perfect insulation (open circuit).
Always discharge the equipment under test after measurement to avoid capacitive shock.
Portable and self-contained power source.
Highly reliable for detecting hidden insulation faults.
Non-destructive testing at rated voltages.
High DC voltage can damage delicate semiconductor components.
Manual cranking requires consistent speed for stable readings.
Routine maintenance of power cables and transformers.
Testing winding continuity in induction motors.
Verifying grounding integrity in industrial installations.
The Megger instrument was originally developed by the company 'Megger' (formerly Evershed & Vignoles).
Option C (Open Circuit) is valid because an infinite resistance reading during a continuity test indicates a broken conductor or open circuit.
D is correct — The Megger is a versatile diagnostic tool capable of identifying insulation degradation (Earth fault), circuit continuity, and open paths by measuring resistance across a high-voltage gradient.
Always remember: 'Megger' is for insulation (high resistance) while a Multimeter (Ohmmeter mode) is typically for low-resistance continuity tests.