Question 2
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(a) (i) State two types of electricity distribution networks.
(e) Name two fire-fighting equipment.
(ii) Explain briefly the two types of electricity distribution networks stated in 2(a)(i).
(iii) List four materials used for overhead line installation.
(b) (i) State two causes of each of the following faults:
I. the motor of an electrical appliance fails to start when switched on;
II. a motor hums, but fails to start.
(ii) Suggest two remedies for each for the faults listed in 2(b)(i).
(c) Calculate the illumination on a working plane at a point A 3 m vertically below a lamp emitting 540 cd.
(d) Name two business models that an entrepreneur can adopt.
Observation
In part (a), many candidates failed to explained the two types of electricity distribution network. Candidates performance was unsatisfactory.
In part (b), Performance was unsatisfactory. (i) the first thing candidates should realize is “No supply” or/and “open circuit” but rather some of them wrote about “low voltage”. (ii) few candidates attempted this question but could not do justice to it since some failed to recognize the unit of measurement as mm/m2 or lux. (iii) almost all candidates did not think of entrepreneur in terms of “sole”, limited liability or forming partnership. Performance was below average.
The expected answers include:
2(ai) Two Types of Electricity Distribution Networks
- Radial
- Ring main
(ii) Radial – feeders emanate from substation and feed specified areas only.
Without return path of the source.
Ring – An electrical system in which distribution points are connected to the main supply in a continuous closed circuit/loop.
(iii) Four Materials used for Overhead line Installation
- Stay wires
- Flying stay
- Insulator
- Cross arm
- Cable/aluminium cable/aluminium conductor
- Lighting/surge arrester
- Pole
(bi) I Two Causes of faults in a Motor of an Electrical Appliance that fails to Start when Switched On
- No supply
- Blown fuse
- Centrifugal switch contact open
- Overhead replay open
- Motor may be burnt
- Open circuit on starter resistance
- Open circuit on field winding.
II Two Causes of fault of a Motor humming but Fails to Start
- Mechanical overload
- Open circuit in the starting winding
- Open circuit in one of the three phases of the three phases of a three-way phase motor
- Low voltage
- Faulty starting capacitor/device
- Worn out bearings
- Open Centrifugal switch
(ii) I. Two Remedies for motor in an Electrical Appliance that fails to Start when
Switched On
- Restore supply
- Change blown fuse
- Change/replace centrifugal switch
- Rewind burnt motor
- Check and close overhead relay.
- Check and correct loose contact on starter resistance.
- Check/correct the continuity of field winding.
II Two Remedies for Motor humming but Fails to Start
- Check belt for alignment
- Wash dirty bearings
- Replace warn-out bearings
- Check and restore supply voltage
- Replace starting capacitor
- Rewind starting winding
- Open circuit windings
Check/ close centrifugal switch
N/B: The unit must be correct to score
(d) Two Business Models that an Entrepreneur can Adopt
- Sole proprietorship
- Limited liability
- Partnership
(e) Two Fire Fighting Equipment
- Fire extinguisher
- Water hose
- Fire fighting vehicle
- Sand pail/water & soap bucket/sand bucket