In this topic, you study the necessity of testing the new installation. And apparatus would you like to use for testing the domestic installation.
All types of electrical installations, domestic and industrial, should be tested and inspected before energising. It must be made sure that there is no short circuit, earth leakage or discontinuity etc., moreover the wiring is done according to the Electricity Rules. According to the Electricity Rule, the new installation or extension of the existing installation shall not be energised by any supplier unless the supplier makes sure that the wiring has been done according to the Electricity Rule and the wiring will not give shock and prove harmful to any human being or supplier. So before connecting the supply the supplier will test the wiring. The instrument generally used for this testing is the megger. An authorised contractor will state and certify that the wiring has been done according to the Electricity Rule and leakage current will not exceed 1/5000th of the total current between either two conductors of opposite polarity or between any live conductor and the earth i.e.
Leakage current = 250/ Insulation resistance in mega Ohm
Megger. The wiring is tested with this instrument. It is used to measure the insulation resistance of the wires in mega ohm. The megger consists of a hand driven d.c. permanent magnet generator. Generally for the domestic wiring purpose the megger of 500 V is used and for power wiring testing 1000 V megger is used. There are two terminals marked as L and E i.e. live and earth. A pointer deflects over a calibrated scale which is divided from O to ∞. The handle should be rotated at 160 r.p.m. Precautions for using the megger. mese following precautions should be carefully observed:
- Generally the voltage of the megger should be double then the voltage rating, for domestic installation 500 V and for industrial installation etc. 1000 V megger is used.
- In no case it should be connecting on the line.
- Before testing the installation, the megger should be tested itself and make sure whether it is in working order or not. For that testing short circuit both L and E terminals Of the megger, on rotating the handle it should show zero.
- In case Of short circuit the megger should show zero and in case of open circuit the megger should show infinity.
- The handle should be rotated at 160 r.p.m. or as mentioned in the instructions supplied by the manufacturer.
- While testing, the connections should be well tight.
- The megger should be handled carefully.