Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 3rd Term
Week: 1
Age: 15 years
Duration: 45 minutes
Subject: Electrical Installation and Maintenance Work
Curriculum Theme: Technology
Previous Lesson: .
Topic: INTRODUCTION TO PROTECTIVE DEVICES
Subject Matter: meaning of protective device, types of protective devices, functions of protective devices, examples of protective devices such as circuit breaker and fuse

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define a protective device.
State at least three functions of protective devices.
List at least two types of protective devices.

Affective Domain:

Appreciate the importance of protective devices in ensuring electrical safety.

Psychomotor Domain:

Identify a circuit breaker and a fuse from displayed examples.
Draw simple sketches of a circuit breaker and a fuse.

Explain the role of protective devices in preventing hazards in the home and community.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Electrical Installation and Maintenance Work.
State Unified Scheme of Work for Senior Secondary Schools.
Electrical Installation Technology for Senior Secondary Schools by A.O. Okoro.

Instructional Materials

The teacher will teach this lesson with the aid of:

Actual circuit breaker
Actual fuse (various types if available)
Chart showing different types of protective devices
Diagrams of electrical circuits with protective devices

Rationale for the Lesson

This lesson helps pupils understand how electrical systems are kept safe from damage and how people are protected from electrical hazards. Understanding protective devices enables pupils to recognise their importance in daily life, both at home and in public spaces, contributing to overall safety awareness.

Prerequisite/Previous Knowledge

Pupils are expected to have a basic understanding of electricity, simple electrical circuits, and the concept of current flow from their previous classes.

Lesson Content/Board Summary

INTRODUCTION TO PROTECTIVE DEVICES

Meaning of Protective Device

A protective device is an electrical component designed to safeguard electrical circuits, equipment, and users from damage or injury caused by abnormal conditions such as overcurrent, short circuits, or earth faults. They automatically interrupt the flow of electricity when a fault occurs.

Functions of Protective Devices

The following are the main functions of protective devices:

To prevent damage to electrical appliances and wiring from excessive current.
To protect individuals from electrical shocks and hazards.
To isolate faulty sections of an electrical circuit, preventing wider system failure.
To ensure the safety and longevity of electrical installations and systems.

Types of Protective Devices

The following are common types of protective devices:

Fuses
Circuit Breakers (e.g., Miniature Circuit Breaker (MCB), Moulded Case Circuit Breaker (MCCB), Residual Current Circuit Breaker (RCCB), Residual Current Breaker with Overcurrent protection (RCBO))
Earth Leakage Circuit Breakers (ELCB)
Surge Protective Devices (SPD)
Relays (in some applications)

Examples of Protective Devices

Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current, typically resulting from an overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation after the fault is cleared.

Fuse

A fuse is an electrical safety device that operates to provide overcurrent protection for an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby interrupting the circuit in which it is connected. Fuses are sacrificial devices; once a fuse has operated (blown), it must be replaced with a new one of the correct rating.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them if they have ever experienced a power outage due to a “trip” or a “blown fuse” at home. The teacher then explains that these events are related to devices designed to protect electrical systems.
Pupils’ Activity: Pupils respond to the questions and share their experiences.
Learning Point: Pupils are introduced to the concept of electrical protection and its relevance.

Step 2: Meaning of Protective Device

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines a protective device, writing the definition on the board. The teacher explains that these devices act as safety mechanisms in electrical circuits.
Pupils’ Activity: Pupils listen attentively, copy the definition into their notebooks, and ask questions for clarification.
Learning Point: Pupils understand the fundamental definition of a protective device.

Step 3: Functions of Protective Devices

Time: 7 minutes
Teaching Skill: Elaboration/Listing
Teacher’s Activity: The teacher explains the various functions of protective devices, such as preventing damage to appliances, protecting users, and isolating faults. The teacher lists these functions on the board.
Pupils’ Activity: Pupils listen, take notes, and contribute ideas on how these functions ensure safety.
Learning Point: Pupils understand why protective devices are important in electrical systems.

Step 4: Types of Protective Devices

Time: 7 minutes
Teaching Skill: Classification/Demonstration
Teacher’s Activity: The teacher displays the actual circuit breaker and fuse. The teacher lists and briefly introduces various types of protective devices, pointing out the displayed examples.
Pupils’ Activity: Pupils observe the displayed devices, listen to the teacher’s explanation, and identify the different types.
Learning Point: Pupils can identify common types of protective devices.

Step 5: Specific Examples: Circuit Breaker

Time: 6 minutes
Teaching Skill: Detailed Explanation/Illustration
Teacher’s Activity: The teacher explains in detail what a circuit breaker is, how it works (detects faults and interrupts current), and highlights its reusability compared to a fuse. The teacher may draw a simple diagram.
Pupils’ Activity: Pupils listen, ask questions, observe the actual circuit breaker, and sketch a simple diagram in their notebooks.
Learning Point: Pupils gain a clear understanding of circuit breakers.

Step 6: Specific Examples: Fuse

Time: 6 minutes
Teaching Skill: Detailed Explanation/Illustration
Teacher’s Activity: The teacher explains what a fuse is, how it functions (melting wire), and emphasizes that it needs replacement after operation. The teacher may draw a simple diagram.
Pupils’ Activity: Pupils listen, ask questions, observe the actual fuse, and sketch a simple diagram in their notebooks.
Learning Point: Pupils gain a clear understanding of fuses.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

What is a protective device?
Mention two functions of protective devices.
List three types of protective devices.
Differentiate between a circuit breaker and a fuse.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization/Consolidation
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of protective devices for safety. The teacher then assigns homework, asking pupils to find out the current ratings of fuses or circuit breakers used in their homes.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils reinforce their understanding and are encouraged to apply learning.

Lesson Keywords

Protective Device – An electrical component that safeguards circuits, equipment, and users from damage due to faults.
Circuit Breaker – An automatically operated electrical switch that protects circuits from overcurrent or short circuits and can be reset.
Fuse – An electrical safety device with a metal wire that melts to interrupt a circuit when current exceeds a safe level, requiring replacement after operation.
Overcurrent – A current exceeding the rated current of equipment or a conductor.
Short Circuit – An abnormal connection between two nodes of an electrical circuit intended to be at different voltages, resulting in a large current.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research different types of circuit breakers (e.g., MCB, RCCB) and their specific applications. For pupils who require more support, the teacher can provide simplified diagrams and allow more time for hands-on observation of the devices, focusing on identifying the basic components and functions.

Note for teachers using this lesson plan

Ensure that actual protective devices are available for demonstration to enhance pupils’ understanding and engagement. Emphasize the practical safety implications of these devices in real-world electrical installations. Encourage pupils to ask questions and share any relevant experiences they might have had with electrical trips or faults at home.