Insulation resistance tester or megger is used to measure insulation resistance of wire and cable. It can check continuity also. The megger is a most important instrument for electricians. Before and after laying the cables, check the insulation resistance. According to I.E. rules the insulation resistance should not be less than one Meg-Ohm.
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What is the insulation resistance?
The resistance offered by the insulation of a conductor to the flow of leakage current is called the insulation resistance.
What will be the effect if insulation resistance is very low?
If the insulation resistance becomes very low, then leakage current will flow through the conductors as a result the energy meter will show high reading due to excess current flowing through the conductor. It will affect human beings also if they touch anybody with very low resistance wires and conductors.
Type of insulation resistance tester or megger
Digital and analogue both type of insulation resistance tester are available. According to voltage different kind of insulation resistance tester or megger is used (i.e. 500 volt, 1000 volt, 2500 volt, 5000 volt etc.).
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How to test the insulation resistance
a. Between conductors (i.e. phase to phase and phase to neutral)
For the insulation resistance test between conductors the “L” and “E” terminal of megger are connect to the outgoing conductors from the main source. The main switch gear or circuit breaker must be off position time of testing. All other circuit breaker will be closed but the entire load (i.e. light and fans) must be disconnected. By rotating the handle of the megger (in case of analogue meter) or pushing the test button (in case of digital megger) the reading will be shown on the megger. Meg. Ohm is the unit of insulation resistance.
b. Between conductors and earth (i.e. phase to earth and neutral to earth)
For the insulation resistance test between conductors and earth the “L” terminal of megger is connect to one of the outgoing conductor from the main source, the other terminal “E” to be connected with an earth terminal. The main switch gear or circuit breaker must be off position time of testing. All other circuit breaker will be closed but the entire load (i.e. light and fans) must be disconnected. By rotating the handle of the megger (in case of analogue meter) or pushing the test button (in case of digital megger) the reading will be shown on the megger. Meg. Ohm is the unit of insulation resistance.
Which materials are used for insulation of electrical lines?
PVC, Ceramic, Insulating Paper and glass are used for insulation of electrical lines.
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