Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Identify different types of electrical circuits.
• Diagnose the nature of faults in circuits.
• Outline the steps for testing circuits for faults.
• Propose solutions to common electrical problems.

Lesson summary

In our homes, schools, and workplaces across Ghana, we depend heavily on electricity. From the lights that allow us to study at night to the sockets that charge our phones and power our appliances, a reliable electrical system is essential. However, these systems can develop faults, leading to inconvenience or even dangerous situations like electrical shocks and fires. This lesson provides the fundamental knowledge and systematic process for safely identifying, testing, and fixing common problems in electrical wiring circuits. This skill is not only crucial for safety but also forms the foundation for a career as a professional electrician.

Lesson notes

A. Safety First! (The Golden Rules)

Before touching any electrical circuit, safety is non-negotiable. A mistake can be fatal. De-energize the Circuit: Always switch off the main switch or the specific circuit breaker at the distribution board (consumer unit) before starting work. Lock-Out, Tag-Out (LOTO): In a professional setting, you would lock the breaker in the OFF position and put a tag on it saying "DANGER: DO NOT SWITCH ON. WORK IN PROGRESS." In a home setting, at least inform everyone in the house not to touch the main switch. Test for Dead: Use a multimeter or voltage tester to confirm that the circuit you are about to work on has no voltage (is "dead"). Test your tester on a known live source first to ensure it is working. Personal Protective Equipment (PPE): Wear appropriate PPE, including insulated gloves, safety glasses, and rubber-soled shoes. Use Insulated Tools: Always use screwdrivers, pliers, and cutters with proper insulation on the handles. B. Part 1: Identifying the Type of Circuit

To fix a problem, you must first understand what you are working on. Common domestic circuits include: Lighting Circuit: Purpose: To supply power to light fittings (bulbs, fluorescent tubes). Characteristics: Typically uses smaller wires (e.g., 1.5 mm²) and is protected by a lower-rated circuit breaker (e.g., 6A or 10A). All lights in a room or section of the house may be on one circuit. Components: Switch, ceiling rose, lamp holder, bulb. Socket Outlet Circuit (Power Circuit): Purpose: To supply power to appliances via 13A or 15A socket outlets. Characteristics: Uses thicker wires (e.g., 2.5 mm² for a ring circuit, 4.0 mm² for a radial circuit) to handle higher currents. Protected by a higher-rated breaker (e.g., 20A or 32A). Types in Ghana: Radial: One cable runs from the distribution board and ends at the last socket. Ring: A cable runs from the distribution board, connects to all sockets in a loop, and returns to the same breaker. This is very common. Components: Socket outlets, circuit breaker. Fixed Appliance Circuit (e.g., Fan, Water Heater, Air Conditioner): Purpose: To supply power to a single, high-power appliance. Characteristics: The circuit is dedicated to only one appliance. The wire and breaker size depend on the appliance's power rating. A fan circuit is similar to a lighting circuit but includes a fan regulator to control speed. Components: Fused connection unit or isolator switch, the appliance itself. C. Part 2: Identifying the Nature of the Fault

Electrical faults are the root cause of problems. The main types are: Open Circuit: What it is: A break or interruption in the path of the current. Electricity cannot flow. Analogy: A bridge collapsing on a road. Cars (current) cannot cross to the other side. Causes: A burnt-out bulb filament, a loose wire at a terminal, a broken switch, or a tripped breaker/blown fuse. Symptom: The appliance or light does not work at all. Short Circuit: What it is: An unintended, low-resistance path for current to flow. This usually happens when the live wire touches the neutral wire directly. Analogy: A shortcut through a crowded market that causes chaos and a massive jam. A very large amount of current flows instantly. Causes: Damaged insulation on wires causing them to touch, faulty appliance wiring, a loose strand of wire bridging two terminals. Symptom: A loud bang, a spark, and the circuit breaker trips or the fuse blows immediately. Overload: What it is: The circuit is drawing more current than it is designed to handle safely. Analogy: Trying to carry 20 bags of cement when you can only safely carry 5. You will eventually collapse. Causes: Plugging too many high-power appliances (iron, kettle, microwave) into one socket outlet extension, or using a faulty appliance that draws too much current. Symptom: The circuit breaker trips after the appliances have been running for a short while. Wires may become hot. Earth Fault: What it is: The live wire touches the metal casing (earthed part) of an appliance or accessory. Causes: Damaged internal wiring in an appliance. Symptom: The circuit breaker or RCD (Residual Current Device) trips immediately. If the earthing is poor, touching the appliance can cause a severe electric shock. D. Part 3: The Systematic Process of Testing the Circuit

Evaluation guide

• Describe the process of servicing electrical wiring circuits
• Focal Area: Processes involved in an electrical circuit.
• Identification of types of Circuit eg lamp, socket outlet,or fan circuit
• Identify nature of fault