Page 104 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

High repturing capacity cartridge fuse
They are cylindrical in shape and are made ceramic body filled with chemically treated filling powder or silica
to quench the arcing quickly without any fire hazard normally silver alloy is used for fusing element and when
it melts due to excessive current it combines with the surrounded sand HRC fuse can open a short circuit with
0.013second. HRC fuses preferred in high power circuits.

Testing of installation: Before a completed installation or an addition to the existing installation is put into
service, inspection and testing shall be carried out in accordance with the INDIAN ELECTRICITY RULE, 1956
The under mentioned are the tests which are generally conducted on the wiring installation before it is actually
connected to the main supply.

1 Insulation test between conductors and earth
2 Insulation test between conductors
3 Continuity or open circuit test
4 Earth continuity test

5 Polarity test
Whenever a wiring system is installed it must be tested before connecting it to the supply. In the event of defects
being found, these shall be rectified as soon as practicable, and the installation re-tested
The instrument used for testing installation is known as mega ohmmeter (megger)or insulation tester.

Megger

A megger is used to perform the installation testing.
It can generate low value direct current when its handle is rotated and measure high value of resistance which is
connected across its terminal. Test is performed on DC volt not less than TWICE of working voltage. If the circuit
is to be operated on 250V supply main, then the megger should generate 500V when its handle is rotated at its
normal speed of 140 to 160 rpm. Its scale is from infinity to zero.

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CITS : Power - Electrician & Wireman - Lesson 20-25 CITS : Power - Electrician & Wireman - Lesson 20-25