Basic Electrical Wiring and Installation
Senior 3 · Physics
Basic Electrical Wiring and Installation
Lesson 4 of 5
30 min
A family in a village has finished building a house and REG has extended the low-voltage line to a pole nearby. Before the first lamp can be switched on, a qualified electrician must install the wiring: a meter, a board of protective devices, cables in the walls, and switches, lamp holders and sockets in every room. This lesson follows that installation, so that you can read a wiring diagram, recognise every part and understand why each step is done the way it is.
Important
Pupils must never open, wire or repair mains fittings: sockets, switches, lamp holders, plugs, the consumer unit or the meter. The 230 V mains can kill. In Rwanda, electrical installation in homes and businesses must be done by qualified technicians; RURA publishes the list of licensed electricians (REG). Everything you build yourself in this lesson uses a 6 V battery.
For some low-income customers in villages, REG supplies a ready board, a pre-wired panel with a lamp, a switch and sockets, which REG installs and earths itself.
| Conductor | Colour (new installations) | Job |
|---|---|---|
| Live (phase), L | Brown (in three-phase supplies: brown, black and grey) | Carries current from the supply at 230 V |
| Neutral, N | Blue | Returns the current; it is close to earth potential |
| Earth, E (protective conductor) | Green and yellow, used for nothing else | Connects metal cases to earth, so that a fault cannot make them live |
These are the colours in REG's standard, following the IEC. Older installations may use red, yellow and blue for the phases and black for the neutral, so an electrician never trusts colours alone: every conductor is tested.
Definition
Radial circuit: a final circuit in which the cable runs from the protective device to each outlet in turn and ends at the last one.
Ring circuit (ring final circuit): a socket circuit in which the cable passes through every outlet and returns to the same protective device, so each outlet is fed from both directions.
Consumer unit (distribution board): the box that contains the main switch, the RCD(s) and the circuit breakers or fuses for all the circuits of a building.
Worked example 1: why a ring?
A socket is 20 m of cable away from the consumer unit. Each conductor of the 2.5 mm² copper cable has resistance with . Compare the resistance of the live conductor feeding the socket in (a) a radial circuit; (b) a 40 m ring with the socket at its middle.
The ring halves the resistance (lesson 1), so the cable heats less and the voltage at the socket drops less for the same current.
Worked example 2: will the breaker trip?
A socket circuit is protected by a 16 A MCB. A 2000 W kettle and a 1000 W iron are switched on together at 230 V. Then a 1500 W heater is added. What happens?
The appliances are in parallel, so their currents add. The MCB trips before the cable overheats; heavy appliances should be on circuits of their own.
| Components and materials | Tools |
|---|---|
| Cables (typically 1.5 mm² for lighting, 2.5 mm² for sockets) with brown, blue and green-and-yellow cores | Insulated screwdrivers, flat and cross-head |
| PVC conduit or trunking, and mounting boxes, to protect cables in walls | Combination pliers and side cutters with insulated handles |
| Consumer unit with main switch, RCD and MCBs | Wire stripper |
| One-way and two-way switches, lamp holders, socket outlets, junction boxes | Approved voltage tester and a multimeter or installation tester |
| Earth rod and earth conductor, cable clips, insulating tape, screws and plugs | Drill, hammer, tape measure, spirit level, marker |
REG advises buying only cables and accessories that meet the standards, and labelling every circuit breaker clearly with the circuit it controls.
Use a 6 V battery, small lamps, switches and connecting wire on a cardboard model of a house. Wire two rooms with a lamp and a switch each, connected in parallel, then add staircase lighting with two two-way switches, so the lamp can be switched from the foot or the top of the stairs:
Draw your circuit with IEC symbols first, then build it, then check it against the drawing.
Warning
Never connect your model to a mains socket, and never use mains cables or fittings in the classroom. The same circuit at 230 V could kill.
Tip
Brown is live, blue goes back, green-and-yellow is earth. Switches and fuses always go in the live
Single-phase electricity explained: wiring diagram and energy meter (The Engineering Mindset). Watch the path from the supply cable through the meter, main switch, RCD and MCBs to the circuits; details such as the colours and ratings in the country shown may differ from Rwanda's.
Practice
Key points
Sources and credits
Written by Ganzaa: the lesson text, the four diagrams, the tables, worked examples and practice exercises. Cable sizes and breaker ratings are typical values.
