Testing Instruments Necessary

Testing Instruments Necessary Points : Testing Instruments Necessary, Megger Insulation Tester, Meaning of Earthing Testing Instruments Necessary This can, be made up very easily by an electrician. It simply consists of a box into which is fitted a small battery (e.g. 6 volts) with a bulb in series with one of the leads. Depends on the job, and terminals could be mounted on the box so that different length leads could be used if necessary.

Megger Insulation Tester This instrument is a portable hand operated generator with a scale giving a reading in ohms from zero to infinity. The voltage output should not be more than 500 volts d.c. Meaning of Earthing To connect any wire, outer covering of wire, outer covering of electrical machines and other appliances to the general mass of earth by wire of negligible resistance is known as Earthing. Metal conduit, outer cover of lead- covered wiring system, table lamp fitted with metallic tube, electric iron, electric heater and other appliances, metallic frame of generator, motor and other electric machines must be properly connected to earth. Earthing does not mean that the earth lead is simply. touched or somehow connected to earth. It means earthing of an installation in such a way that the earth lead is in constant touch with wet soil and the leakage current is always discharged to earth without causing danger. Earth lead may be connected with a water pipe or an iron beam grouted deep into the earth if it is available nearby. But usually the house wiring and specially the outer frames of machines and other electrical appliances are earthed with earth lead connected to separate earth electrode. Again, if the supply pressure exceeds 125 volts, the outer frame of each machine and apparatus should be connected to earth by two separate and distinct earth connectors.

Where supply pressure is only 230-volt, the earth lead of the wiring or installation may be connected with the earth terminal provided by the supplier. In case no earth terminal is provided by the supplier, a separate earthing arrangement is to be made by the consumer. But in case of 3-phase a.c. supply one earth read of the wiring is to be connected with the earth terminal provided by the supplier and another earth lead of the same wiring is to be connected with the separate earthing arrangement made by the consumer himself.