Page 285 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Rated DC Voltage Rated Resistance

250 V 20 megohms
50megohms

500 V 20 megohms
100 megohms
1000 megohms
1000 V 200 megohms
2000 megohms
20000 megohms

2500 V 5000 megohms
50000 megohms
5000 V 100000 megohms

Precautions
• A meg ohmmeter should not be used on a live system.
• The handle of the meg ohmmeter should be rotated only in clock wise direction.
• Do not touch the terminals of a meg ohmmeter while conducting a test.

• Support the instrument firmly while operating.
• Rotate the handle at slip speed.
Uses of megger: To check the insulation resistance and to check the continuity.
Earth resistance tester(earth megger)

Earth megger consists of
1 A hand driven generator
2 Current reverser
3 Synchronous rotary rectifier
4 An ohm meter

Functions
1 Hand driven generator

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CITS : Power - Electrician & Wireman - Lesson 50-53