Lesson Notes By Weeks and Term v4 - SHS 3
CIRCUITS AND MACHINES
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CIRCUITS AND MACHINES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Engineering
Class: SHS 3
Term: 2nd Term
Week: 6
Grade code: 3.2.1.LI.4
Strand code: 2
Sub-strand code: 1
Content standard code: 3.2.1.CS.1
Indicator code: 3.2.1.LI.4
Theme: ENE RGY SYSTEMS
Subtheme: CIRCUITS AND MACHINES
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In our daily lives in Ghana, from the local corn mill operator in the market to the technician at the VRA dam, and even in our own homes using blenders and fans, we interact with electrical machines. These machines make our work easier and our lives more comfortable. However, the energy that powers them can be extremely dangerous if not handled with respect and caution. This lesson focuses on the critical safety measures we must all know and practice to prevent accidents, injuries, and even death when working with or around electrical machines. Understanding these principles is not just for engineers; it's a life skill for everyone.
This section breaks down the fundamental principles of electrical safety. A. The Three Main Categories of Electrical Hazards
When we talk about danger from electrical machines, it usually falls into one of these three categories: Electric Shock and Electrocution: This is the most well-known danger. It happens when a part of the human body completes an electrical circuit, allowing current to pass through it. The severity depends on the voltage, the path the current takes, and the duration. A small shock might just be painful, but a large one can cause severe burns, stop the heart, and lead to death (electrocution). Example: A welder at a Kokompe workshop touches a live wire with a faulty welding machine while standing in a puddle of water. The water provides a low-resistance path for the current to flow through his body to the ground, resulting in a severe shock. Electrical Fires and Explosions: Faulty wiring, overloaded circuits, or sparks from a motor can ignite flammable materials in the surrounding area. Example: A corn mill operator in Makola Market keeps plugging multiple high-power machines into one extension cord. The cord overheats, melts the insulation, and starts a fire that ignites nearby sacks of corn husks. Mechanical Injuries: Electrical machines have moving parts (e.g., the shaft of a motor, the blades of a fan, the belt of a generator). If a person's clothing, hair, or limbs get caught in these moving parts, it can cause serious physical injury, like cuts, fractures, or amputation. Example: A student working on a fufu-pounding machine in a school canteen wears a loose-fitting school uniform. The sleeve of the shirt gets caught in the machine's moving belt, pulling their arm into the mechanism. B. General Safety Principles and Measures
To prevent these hazards, we use a combination of safety measures that can be grouped into three areas: Personal Safety, Equipment Safety, and Workplace Safety. i. Personal Safety (The Operator)
This is about what YOU, the operator, must do. Personal Protective Equipment (PPE): This is gear worn to minimise exposure to hazards. Insulated Gloves: Made of rubber, to protect hands from shock. Safety Goggles/Face Shield: Protects eyes from sparks, flying debris. Safety Boots: Often have rubber soles for insulation and steel toes to protect against falling objects. Hard Hats: Protect the head from falling objects, essential in construction or industrial sites. Awareness and Behaviour: NEVER operate electrical equipment with wet hands or in wet conditions. Water drastically lowers the body's resistance to electricity. Avoid wearing loose clothing, jewellery, or long, untied hair around machines with moving parts. Always assume a circuit is LIVE until you have personally de-energized it and tested it. Use the "one-hand rule" when working on live circuits (if absolutely necessary and you are qualified), keeping one hand in your pocket to prevent current from passing across your chest and heart. ii. Equipment Safety (The Machine)