Question 3
- (i) Define final sub-circuit
(ii) List three final sub-circuits asscociated with domestic wiring.
- State :
- the difference between a cable and a conductor;
- one factor that must be considered in the choice of cable sizes for wiring.
Observation
The expected answers were;
- (i) Final sub-circuit is that circuit connected between an electrical load and live, neutral and earth points in Consumer Control Unit (CCU) for the purpose of supplying electrical energy to the load.
(ii) Final Sub circuits associated with domestic wiring
- Ring circuit
- Radial Circuit
- Lighting Circuit
- Heater Circuit
- Motor Circuit
- (i) Cable is a length of insulated single (solid or stranded) wire while conductor is the part of cable which offers very low resistance to the flow of current.
(ii) Factors to be considered in the choice of cable size for wiring
- Length of the cable
- Current demand by its load
- Cross sectional area
- Ambient temperature
- Environment
Many of the candidates who attempted this question did not understand final sub-circuit and therefore performed poorly.