Lesson Notes By Weeks and Term v3 - Senior Secondary 1

Lesson Video

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Performance objectives

• Interpret circuit and wiring diagrams.
• Identify electrical accessories from a drawing.
• Draw a simple power system diagram.
• Draw a wiring diagram for a living room.

Lesson summary

In terpret working drawing ( circuit and wiring diagrams) Identify the accessories required for a job from the drawing Draw the circuit diagram of a generation transmission and distribution system. Draw the wiring diagram of a living room and locate the positions of various accessories on the diagram.

Lesson notes

A working drawing, in the context of electrical installation, is a technical drawing that provides detailed graphical information for the construction, installation, and maintenance of an electrical system. It acts as a universal language for electrical professionals, ensuring clarity and precision regardless of spoken language. Its primary purpose is to convey all necessary information clearly and unambiguously. 2.2.1 Circuit Diagram (Schematic Diagram)

Definition: A circuit diagram, also known as a schematic diagram, shows the functional relationship between the components of an electrical circuit. It focuses on how a circuit works rather than where the components are physically located or how the wires are routed.

Purpose: To illustrate the principle of operation, the sequence of connections, and the interaction of components.

Characteristics: Uses standardised electrical symbols to represent components. Lines represent conductors (wires), and junctions represent connections. Does not typically show the physical size or exact placement of components.

Standard Electrical Symbols: Students must be familiar with common symbols as specified by international (e.g., IEC, ANSI) and national standards (e.g., SON).

Common Symbols and their Meanings: Conductor (Wire): `—` Junction (Connected Wires): `—•—` (dot indicates connection)

No Connection (Crossing Wires): `—╳—` or `— ∩ —` (no dot)

Ground/Earth: `≡` Resistor: `—^v^—` Capacitor: `—| |—` (non-polarised) or `—| |— +` (polarised)

Inductor/Coil: `—∩∩∩—` Fuse: `—▭—` (rectangle with line through)

Circuit Breaker (Single Pole): `—|/ —` (diagonal line indicates breaking mechanism)

Lamp/Light Bulb: `—X—` (circle with cross) or `—○—` (circle with filament symbol inside)

Battery (DC Source): `—| |—|—` (long line positive, short line negative)

AC Source: `—~—` (circle with sine wave) Switch (SPST - Single Pole, Single Throw): `—o / o—` (open contacts)

Two-Way Switch: `—o / o` and `—o / o` (two positions)

Intermediate Switch: `—o / o \ o—` (crossing contacts)

Socket Outlet (General Purpose): `—▭—` (rectangle with circles for holes) or `—☉—` (circle with lines inside)

Electric Motor: `—M—` (circle with 'M' inside)

Electric Bell: `—B—` (circle with 'B' inside)

Ammeter: `—A—` (circle with 'A' inside)

Voltmeter: `—V—` (circle with 'V' inside)

Distribution Board (DB): `—▭—` (rectangle representing the board) 2.2.2 Wiring Diagram Definition: A wiring diagram shows the actual physical layout of electrical components and how they are interconnected with wires within a specific space (e.g., a room, a building floor plan). It details the routing of cables, the exact locations of switches, sockets, lights, and other accessories.

Purpose: To guide the installer in physically connecting components, indicating cable runs, and precise placement.

Characteristics: Often superimposed on architectural floor plans. Uses simplified symbols or conventional representations of components. Shows the exact physical positions relative to walls, doors, windows. Indicates the number of conductors in a cable run (e.g., by adding tally marks to the line). Distinction between Circuit and Wiring Diagrams: Circuit Diagram: "What happens?" (functional).

Wiring Diagram: "Where are things and how are they physically connected?" (physical layout). Interpreting working drawings involves understanding the symbols, lines, and annotations.

Symbols: Each symbol represents a specific component or function. Recognition is key.

Lines: Lines represent conductors. Different line types or numbers on lines can indicate the type of cable, number of conductors, or conduit.

Text/Annotations: Labels, notes, and schedules provide additional information such as voltage, current ratings, cable sizes, and component specifications.

Layout: For wiring diagrams, the relative positions of symbols on the floor plan indicate the actual placement of accessories. From a working drawing (especially a wiring diagram), students should be able to identify: Switches: Single-pole, two-way, intermediate.

Lighting Points: Ceiling roses, wall lamps, fluorescent fittings.

Socket Outlets: 13A switched/unswitched, 15A round pin, shaver sockets.

Fan Points: Ceiling fan, exhaust fan.

Bell Points: Doorbell, chime unit.

Distribution Board (DB): Consumer unit, fuse box.

Cooker Unit: Dedicated high-current socket.

Water Heater Point: Dedicated power supply.

Real-life applications

Domestic and Commercial Electrical Installations: Electricians in Nigeria constantly rely on working drawings to install wiring, fixtures, and appliances in homes, offices, and shops. For instance, when a new house is being built in Abuja or Lagos, the electrician interprets the architectural and electrical plans to correctly run conduits, place switches, sockets, and light fittings according to the homeowner's requirements and safety standards.

Troubleshooting and Maintenance: When an electrical fault occurs in a facility (e.g., a power outage in a specific section of a market in Onitsha), electricians use the existing wiring diagrams to quickly trace the circuit, identify the faulty component (e.g., a blown fuse, a tripped circuit breaker, or a loose connection), and effect repairs efficiently. Without these drawings, troubleshooting would be significantly harder and more time-consuming.

Electrical Safety and Regulations: Correctly drawn and interpreted working drawings ensure that electrical installations comply with Nigerian Electrical Safety Standards and other relevant building codes. This prevents hazards like electrical fires, shocks, and overloaded circuits, thereby protecting lives and property in communities across Nigeria. For example, a drawing can specify the correct gauge of wire for a particular load, preventing overheating and potential fire hazards, which is crucial in densely populated areas.

Teacher activity

• Illustrate different symbols
• Explains the in ter connection or symbols.
• Illustrate how to use scale to determine size and length of building and cables.
• Identify different accessories

Evaluation guide

• This section outlines how to assess students' understanding and mastery of the learning objectives.
• 1 Formative Assessment:
• Observation: Monitor students' participation in discussions, their ability to draw symbols accurately during class activities, and their approach to interpreting diagrams.
• Question and Answer: Ask oral questions during the lesson to gauge immediate comprehension (e.g., "What does this symbol represent?", "Where would you place a switch in a room?").
• Quick Check: Have students quickly sketch 3-5 symbols at the start or end of the class.

Reference guide

• for a project, thus managing costs and reducing waste.
• Ensure safety by following prescribed wiring paths and component specifications.
• Communicate effectively with other professionals in the construction industry.
• Key Concepts and Explanations
• This section provides a detailed explanation of "Working Drawing" and its related concepts, essential for effective teaching.
• 1 What is a Working Drawing?