Sunday, 5 April 2015

Before giving the power some tests must be done.



In my previous post, I have discussed about the instruction of wiring. Now, suppose you have made the wiring complete and going to power it up. Stop one second, are all the connections tested?
Before giving the power some tests must be done.
1.   Insulation resistance test
This test is done to know whether there is any leakage in the conductors. There are mainly two types of leakage.
(a)between phase and neutral, (b)between conductors and earth.
For the first part of the test, the main switch should be opened and all electrical appliances removed from the circuit. All controlling switches should be closed. The resistance between phase and the neutral conductors is measured with a 500 volt megger.

 Resistance of each circuit should not be3 less than 10MegaOhm.
For second part of the testing between conductor and earth, all controlling switches should be closed, all lamps put in position, all fuses provided and phase and neutral conductors short circuited at the main switch. The insulation resistance between conductors and earth is then measured. This value should not be less than 5ohm.
2.   Continuity Test
In this test, all the fuses and links are provided and switches closed. All outlets are shorted one by one and continuity checked. The resistance between phase and neutral is measured with a 500v megger at the main switch. the value shouls be nearly zero.
3.   Polarity test
4.   This test is done to ensure that switches are controlling the phase wires and not the neutral wires. One terminal of the megger is connected to the phase and main switch and the other to the terminal of the control switch. the megger in this condition should read zero, otherwise it indicates that the switches are controlling the neutral wire.     
5.   Earth Resistance Test
For this, one terminal of earth tester is connected with the earth to be tested and two other terminals with two earthing  electrodes placed at distances of 22.5m and 45m respectively. the tester is run with constant speed for about a minute. The value of resistance should not be more than 2ohms for good condition.  




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