Lesson Notes By Weeks and Term v4 - SHS 3
≈SUBSTRUCTURE AND SUPERSTRUCTURE
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≈SUBSTRUCTURE AND SUPERSTRUCTURE
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Applied Technology
Class: SHS 3
Term: 1st Term
Week: 15
Grade code: 3.3.2.LI.3
Strand code: 3
Sub-strand code: 3
Content standard code: 3.3.2.CS.1
Indicator code: 3.3.2.LI.3
Theme: BUILDING CONSTRUCTION TECHNOLOGY
Subtheme: ≈SUBSTRUCTURE AND SUPERSTRUCTURE
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This lesson focuses on the systematic process of installing electrical services in a building, a crucial component of the superstructure finishing works. Once a building's main structure (walls, floors, roof) is complete, essential services like electricity must be installed to make it habitable and functional. In Ghana, every home, school, and office depends on a safe and reliable electricity supply. Understanding the correct sequence, or "schedule of works," is vital for safety, efficiency, and ensuring the installation meets the standards of the Electricity Company of Ghana (ECG).
What is a "Schedule of Works"? In construction, a schedule of works is a detailed, step-by-step list of all tasks that need to be completed for a project. It specifies the correct order in which these tasks must be done. Think of it as a recipe for constructing or finishing a part of a building. For electrical installation, following the schedule is crucial because some tasks must be done before walls are plastered, while others can only be done after painting is complete.
The Five Main Phases of Electrical Installation Works
The installation of electricity in a new building can be broken down into five logical phases. Phase 1: Preliminary and Pre-installation Works This is the planning phase, which happens before any physical work starts on site. Agreement & Documentation: The property owner signs an agreement with the Electricity Company of Ghana (ECG) for a new service connection. The owner must also have an approved building permit and architectural drawings. Electrical Design: A certified electrician or electrical engineer designs the electrical layout. This plan shows the exact location of every: Light point (bulb holder, chandelier) Switch Socket outlet (plug) Special outlets (for air conditioners, water heaters, cookers) The location of the Consumer Unit (also known as the fuse box or breaker box). Site Inspection: The electrician visits the site to assess the building and plan the routes for cables. Phase 2: First Fix (Carcassing or Rough-in) This is the "hidden" work done *after* the blockwork is complete but before the walls are plastered. The goal is to put in all the infrastructure that will later hold the cables and accessories. Chasing: The electrician cuts grooves or channels (called 'chases') into the block walls and concrete floors where the electrical pipes will run. Conduit and Trunking Installation: Conduits: These are plastic (PVC) or metal pipes that are laid inside the chases in the walls, floors, and ceiling slabs. They protect the electrical cables from damage and allow them to be replaced later if needed. Trunking: These are rectangular plastic or metal channels, often used on the surface of walls when chasing is not possible, or to carry many cables neatly. Back Box Installation: Metal or plastic boxes (called 'back boxes') are fitted securely into the walls at the locations where switches and sockets will be placed. The conduits run into these boxes. Earthing Provision: A copper rod (earth rod) is driven deep into the ground outside the building. A main earthing cable is run from this rod to the planned location of the consumer unit. This is a critical safety step.
*Example:* Imagine you want a socket for your TV. During the First Fix, the electrician will cut a channel from the floor up the wall, fix a plastic pipe (conduit) inside it, and terminate it in a square plastic box (back box) which is set flush with the blockwork. Phase 3: Cable Pulling (Wiring) This phase takes place after the First Fix is complete and usually after the walls have been plastered, but before final painting. The electrician pulls the correct size and colour of insulated copper cables through the conduits that were installed earlier. A 'draw wire' or 'fish tape' is often used to pull the cables through the long pipes. Different circuits use different cable sizes. For example: 1.5 mm² cable: Used for lighting circuits. 2.5 mm² cable: Used for socket outlet circuits. 4.0 mm² or 6.0 mm² cable: Used for high-power appliances like water heaters or air conditioners. The cables are left with extra length hanging out of each back box, ready for the next phase. Phase 4: Second Fix (Finishing) This is the final installation stage, carried out after plastering, tiling, and painting are complete. It involves fitting all the visible electrical accessories. Installing Accessories: The electrician connects the cables to and screws in place: Socket outlets Switches Light fittings (e.g., bulb holders, ceiling roses, downlights) Cooker control units, fan controllers, etc. Consumer Unit Finalisation: All the circuit cables are neatly terminated inside the consumer unit. Each circuit is connected to a specific Miniature Circuit Breaker (MCB). The main supply cable from the meter position is also connected. Phase 5: Testing, Inspection, and Commissioning This is the final and most critical phase for safety and functionality. Testing: The certified electrician performs a series of tests with special instruments to ensure the installation is safe. These include: Insulation Resistance Test: Checks that cables are not damaged. Polarity Test: Ensures live, neutral, and earth wires are connected correctly. Earth Continuity Test: Confirms that the safety earth connection is complete. ECG Inspection & Metering: The electrician submits a completion certificate. An inspector from ECG visits the site to verify that the installation complies with the Ghana Electrical Wiring Regulations. If it passes, ECG will connect the building to the national grid and install the electricity meter. Commissioning: The electrician switches on the power for the first time, tests every single light and socket to ensure they work correctly, and then officially hands over the completed installation to the property owner.