Lesson Notes By Weeks and Term v4 - SHS 3
ELECTRICAL SYSTEMS DESIGN
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ELECTRICAL SYSTEMS DESIGN
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Subject: Applied Technology
Class: SHS 3
Term: 2nd Term
Week: 11
Grade code: 2.4.1.LI.10
Strand code: 4
Sub-strand code: 1
Content standard code: 2.4.1.CS.1
Indicator code: 2.4.1.LI.10
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRICAL SYSTEMS DESIGN
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In Ghana, many homes are filled with essential electrical appliances like electric irons, kettles, blenders, and fans. When these items stop working, our first thought is often to throw them away and buy a new one, which can be very expensive. However, many "spoilt" appliances have simple faults that can be easily and safely repaired. This lesson introduces the fundamental skills of appliance servicing. By learning how to diagnose and fix common faults, you can save money for your family, reduce electronic waste, and even develop a skill that can earn you an income. This is a practical lesson that empowers you to become a problem-solver in your own home and community.
2.1 What is Appliance Servicing? Appliance servicing is the process of inspecting, testing, diagnosing, and repairing electrical appliances to restore them to their proper working condition. It is a systematic process that requires careful observation, logical thinking, and the safe use of testing tools.
Key Terms: Fault: A defect or problem in a circuit or component that prevents the appliance from functioning correctly. Diagnosis: The process of identifying the nature and cause of a fault. Continuity: An unbroken, complete path for electric current to flow. A component with continuity will allow electricity to pass through it. Open Circuit: A break in the path of the current. A component with an open circuit (e.g., a blown fuse or broken wire) will not allow electricity to pass. This is a common fault. Short Circuit: An unintended, low-resistance path for current to flow, often causing fuses to blow or wires to overheat. This is a dangerous fault. 2.2 Common Appliances and Their Operation To diagnose a fault, you must first understand how the appliance is supposed to work.
A. Electric Pressing Iron Function: To use heat to remove wrinkles from clothes. Principle of Operation: It works on the principle of the heating effect of electric current (Joule's Law). Key Components: Power Cord & Plug: Delivers electricity from the wall socket. Thermal Fuse: A safety device that cuts off power permanently if the iron overheats dangerously. Thermostat: A switch that automatically turns the heating element on and off to maintain the selected temperature. Heating Element: A resistor that gets very hot when current passes through it. It is usually embedded in the soleplate. Indicator Lamp: A small light (usually neon) that shows when the heating element is receiving power.
B. Electric Kettle Function: To boil water quickly. Principle of Operation: Also uses the heating effect of electric current. Key Components: Base and Power Cord: The base connects to the mains power, and the kettle sits on it to receive electricity. Heating Element: A powerful resistor, usually concealed at the bottom, that heats the water. Automatic Switch/Thermostat: A switch, often using a bimetallic strip, that senses steam or high temperature and automatically cuts off power when the water boils. Thermal Cut-out: A safety fuse to prevent the kettle from boiling dry and catching fire.