Observation

        This is a test of practical question, and majority of the candidates responded to it.
       In part (a), majority of the candidates could name the labelled parts, and state one
       function of each of the labeled parts.
       In part (b), only few candidates gave two applications of the instrument.
       In part (c), majority of the candidates could not outline four steps in the procedure
       of operating the testing instrument.
       In part (d), majority of the candidates could list five types of measuring instruments
       used in an electrical workshop.

            The expected answers include:

       5(a)(i)   Parts of Megger insulation tester labelled I, II, III, and  IV
I   -   Generator  
I I -   Scale
III - Ohmmeter
IV-  Pointer     

• Function of the parts

 -    the generator is used to generate current to the ohmmeter
-     the reading is taken from the scale
-     ohmmeter is used to measure the quantity/valve of resistance
-     the pointer indicates the value measured                                                                                                                                              

(b) Minimum reading of megger insulation tester

     (i)   1 MΩ/ 1 mega ohm (between conductors) OR 0.5MΩ (between conductor and general
mass of  earth )

      (ii)   Applications of megger insulation tester

 -   the instrument is used to measure the insulation resistance between poles
-   it is used to measure insulation resistance between like conductor and
metalwork/earth of the installation

• Precautions to be taken when using megger insulation tester

  -    ensure that all loads are removed before commencing testing with the instrument

•  when generating voltages, care should be taken not to touch the lead to avoid shock
•  the lead of the megger should not be short circuited to avoid damaging the instrument
•  the handle of the Megger should be handled with care so that the voltage being

 generated should be gradual                                                                


(c)         Steps in procedure of operating megger insulation tester

-    ensure that all loads are removed before commencing testing with the instrument
-   wind the generator to generate voltage
-    take the readings from the scale
-    interpret the reading taken

(d)     Types of measuring instrument used in an electrical workshop

     (i)                -    voltmeter
-    ammeter
-    tachometer
-    ohmmeter
-    photometer
-    micrometer screw gauge
-    standard wire gauge
-    wattmeter
-    insulation resistance/Megger tester
 

  (ii)   Functions of the instruments in d (i)

   -    voltmeter   -   to measure  voltage
-    ammeter    -   to measure current
-    tachometer – to measure speed
-    micrometer screw gauge – to measure diameter of wire
-    standard wire gauge – to measure diameter of wire
-     ohmmeter – to measure resistance
-     photometer – to measure light intensity OR to measure intensity of light
-     wattmeter– to measure power/energy
-     insulation resistance /Megger tester- to measure insulation resistance
(to measure earth fault) of an installation