Elect Installation & Maintenance Work 2, WASSCE (SC), 2018

Question 5

 

  1. The diagram below shows the layout of a kitchen.

(i)        Reproduce the diagram to specification.
(ii)       Indicate the appropriate position of each of the following accessories on the diagram in 5(a):
            I.          cooker unit;
            II.         2 way switch;
            III.       13 A socket outlet;
            IV.       15 A socket outlet
            V.        incandescent lamp;
            VI.       4-way MCB consumer unit.
(iii)      State the correct cable size for each of the accessories in 5(a)(i)

            (b)       Complete the table below.
(i)        Faults associated with contactor.


Causes

Faults

I.     Contactor not energising.

 

II.    Circuit not completed after contactor             is energised  

 

III.   Contactor vibrating.

 

IV.   Welded contacts of the contactor.

 

                       
(ii)       State two factors that should be considered before using a cable.

  (iii)      List four factors influencing earthing system.

Observation

 

In part (a), many candidates who attempted this part performed above average. Candidates were given full mark for having the knowledge that the one 2-way switch should be by the door, the incandescent lamp should be at the centre of the room and the cooker control unit should be close to the window.

In part (b), performance was poor as the question threw the candidates off balance. Many candidates performed poorly.

The expected answers include:

 

Specification                                                                                                 
            Layout                                                                                                

(ii)       I           -           cooker unit                  -   K                                                   
II          -           2-way switch              -   N                                                    
III        -           13 A Socket outlet      -   (L,P,O)                                          
IV        -           15 A Socket outlet      -   (L,P,O)                                          
V         -           incandescent lamp      -                                                          
VI        -           4 way MCB Consumer unit    - (4AO)                                    
NB:  There must not be duplication of letters                                  

 

(iii)      i.      Cooker unit                                -            4 mm2                                    
ii.     2-way switch                             -            1 mm2/1.5mm2                      
iii.     13A socket                               -            2.5 mm2                                 
iv.     15A Socket outlet                     -           2.5 mm2                                    
v.       Incandescent lamp                   -            1 mm2/1.5mm2                     
vi.      4 – way MCB Consumer unit  -                                                                     
(bi)      Faults Associated with Contactor
I           -           Open circuit/short circuit coil/no supply                               
II          -           Open circuit of the line conductors/high resistance on the contact
III        -           Dirty contact                                                                          
IV        -           partial contact/loose contact/excess current                          

(ii)       Two Factors that should be considered before Using a Cable

    • Cable size
    • Type of installation/building
    • Type of insulation
    • Environment
    • Load
    • Cost
    • Durability/life span

(c)       Four Factors Influencing Earthing System

    • Ambient temperature
    • Application/environment
    • Load current/max rated current
    • Suitable voltage drop
    • Installation data
    • Short circuit current
    • Grouping
    • Type of sheath Deposition