Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 3rd Term
Week: 4
Age: 15 years
Duration: 45 minutes
Subject: Electrical Installation and Maintenance Work
Curriculum Theme: Technology
Previous Lesson: Circuit Breaker: Meaning and Types.
Topic: CURRENT OPERATED CIRCUIT BREAKER
Subject Matter: meaning of current operated circuit breaker, types of current operated circuit breaker, principles of operation of current operated circuit breaker, single phase and three phase current operated circuit breaker examples

Specific Objectives

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

Cognitive Domain:

Define a Current Operated Circuit Breaker (COCB).
Identify and list different types of Current Operated Circuit Breakers.
Explain the principles of operation of a Current Operated Circuit Breaker.
Distinguish between single-phase and three-phase Current Operated Circuit Breakers.

Affective Domain:

Appreciate the importance of Current Operated Circuit Breakers in ensuring electrical safety.
Understand the need for proper installation and maintenance of safety devices.

Psychomotor Domain:

Observe and identify the physical components of various Current Operated Circuit Breakers.
State the basic principle of operation of a Current Operated Circuit Breaker.

Participate in discussions about electrical safety measures in homes and workplaces.

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 Practice for Senior Secondary Schools, by A.O. Alabi.
https://www.electricaltechnology.org/2019/08/rccb-rcd-working-principle.html
https://www.theengineerspost.com/types-of-current-operated-circuit-breakers/

Instructional Materials

The teacher will teach this lesson with the aid of:

A single-phase Current Operated Circuit Breaker.
A three-phase Current Operated Circuit Breaker.
Charts showing diagrams of COCBs and their internal components.
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils understand important safety devices used in electrical installations. Knowledge of Current Operated Circuit Breakers enables pupils to identify and appreciate mechanisms that protect against electric shock and fire hazards, contributing to safer electrical environments in daily life.

Prerequisite/Previous Knowledge

Pupils are expected to have basic knowledge of electrical terms such as current, voltage, circuits, and the concept of electrical safety, including the function of fuses.

Lesson Content/Board Summary

CURRENT OPERATED CIRCUIT BREAKER

Meaning of Current Operated Circuit Breaker (COCB)

A Current Operated Circuit Breaker (COCB), also known as a Residual Current Device (RCD) or Earth Leakage Circuit Breaker (ELCB), is an electrical safety device designed to quickly disconnect a circuit when it detects an imbalance in the electric current. This imbalance, often caused by an earth fault or leakage current, indicates a risk of electric shock or fire.

Types of Current Operated Circuit Breaker

The following are common types of Current Operated Circuit Breakers:

Residual Current Circuit Breaker (RCCB): This device detects earth leakage currents and disconnects the circuit. It does not provide protection against overcurrent or short circuits.
Residual Current Breaker with Overcurrent (RCBO): This is a combined device that provides protection against earth leakage, overcurrent, and short circuits. It combines the functions of an RCCB and a Miniature Circuit Breaker (MCB).
Earth Leakage Circuit Breaker (ELCB) – Voltage Operated: An older type that detects voltage on the earth wire. Less common now due to limitations compared to current-operated RCDs.

Principles of Operation of Current Operated Circuit Breaker

Current Operated Circuit Breakers work on the principle of detecting current imbalance. In a healthy circuit, the current flowing to a load should be equal to the current returning from it. A COCB continuously monitors the current in the live and neutral conductors. If there is an earth fault, some current will leak to earth, creating an imbalance between the live and neutral currents. When this imbalance exceeds a predetermined threshold (e.g., 30mA), the COCB quickly trips, interrupting the power supply and preventing electric shock.

Single-Phase and Three-Phase Current Operated Circuit Breaker Examples

Current Operated Circuit Breakers are available for both single-phase and three-phase electrical systems:

Single-Phase COCB: Used in domestic and small commercial installations where the power supply consists of one live wire, one neutral wire, and an earth wire. It monitors the current in the live and neutral conductors.
Three-Phase COCB: Used in industrial and larger commercial installations with a three-phase power supply. It monitors the current in all three live phases and the neutral conductor (if present) to detect any imbalance.

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, reviews the previous lesson briefly, and then introduces the topic by asking pupils about the importance of safety devices in electrical installations. The teacher then displays a Current Operated Circuit Breaker.
Pupils’ Activity: Pupils respond to questions, recall previous knowledge, and observe the displayed device.
Learning Point: Pupils are prepared for the lesson and understand the relevance of electrical safety devices.

Step 2: Meaning of Current Operated Circuit Breaker

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher explains the meaning of a Current Operated Circuit Breaker (COCB), emphasizing its role as a safety device for detecting earth leakage currents and preventing electric shock.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification.
Learning Point: Pupils define what a Current Operated Circuit Breaker is.

Step 3: Types of Current Operated Circuit Breaker

Time: 8 minutes
Teaching Skill: Classification/Demonstration
Teacher’s Activity: The teacher explains and displays different types of COCBs such as RCCBs and RCBOs, highlighting their specific functions and differences.
Pupils’ Activity: Pupils observe the different types, identify their features, and note down their names and functions.
Learning Point: Pupils can identify and list various types of Current Operated Circuit Breakers.

Step 4: Principles of Operation of Current Operated Circuit Breaker

Time: 10 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains in detail how a COCB works by monitoring current balance between live and neutral wires. The teacher uses diagrams or the displayed devices to illustrate the tripping mechanism when an imbalance occurs.
Pupils’ Activity: Pupils listen, observe the illustrations, ask questions about the working principle, and discuss its importance.
Learning Point: Pupils understand and can explain the principles of operation of a COCB.

Step 5: Single-Phase and Three-Phase Current Operated Circuit Breaker Examples

Time: 7 minutes
Teaching Skill: Differentiation/Application
Teacher’s Activity: The teacher explains the difference between single-phase and three-phase COCBs, showing the respective devices and discussing their typical applications in homes versus industrial settings.
Pupils’ Activity: Pupils observe the examples, ask questions to differentiate between them, and understand their appropriate uses.
Learning Point: Pupils can distinguish between single-phase and three-phase COCBs and their applications.

Step 6: 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 Current Operated Circuit Breaker?
Mention two types of Current Operated Circuit Breakers.
Briefly explain the principle of operation of a COCB.
State one difference between a single-phase and a three-phase COCB.

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
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of COCBs for electrical safety. The teacher then gives homework.
Pupils’ Activity: Pupils listen to the summary and note down the homework.
Learning Point: Pupils consolidate their understanding of the lesson.

Lesson Keywords

Current Operated Circuit Breaker (COCB) – An electrical safety device that quickly disconnects a circuit when it detects an imbalance in current due to an earth fault.
Residual Current Device (RCD) – Another name for a Current Operated Circuit Breaker.
Residual Current Circuit Breaker (RCCB) – A type of COCB that protects only against earth leakage, not overcurrent.
Residual Current Breaker with Overcurrent (RCBO) – A type of COCB that combines protection against earth leakage, overcurrent, and short circuits.
Earth Leakage – The flow of current from a live conductor to the earth due to insulation failure or accidental contact.
Tripping – The action of a circuit breaker opening to interrupt the flow of electricity.

Differentiation

For visual learners, the teacher will use charts, diagrams, and actual COCBs. Auditory learners will benefit from clear explanations and discussions. Kinesthetic learners will be engaged through observing and handling the physical devices. Pupils who grasp concepts quickly can be encouraged to assist peers who may be struggling, while the teacher provides additional explanations and examples for those needing more support.

Note for teachers using this lesson plan

Ensure that the actual Current Operated Circuit Breaker devices are available and safe for demonstration. Emphasize practical applications and real-life scenarios where these devices protect lives and property. Encourage pupils to ask questions and share any experiences related to electrical safety. Safety precautions must be observed during any demonstration involving electrical components.