Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 3rd Term
Week: 7
Age: 15 years
Duration: 45 minutes
Subject: Electrical Installation and Maintenance Work
Curriculum Theme: Technology
Previous Lesson: Installation of Current Operated Circuit Breaker.
Topic: INTRODUCTION TO VOLTAGE OPERATED CIRCUIT BREAKER
Subject Matter: meaning of voltage operated circuit breaker, principle of operation of voltage operated circuit breaker, schematic diagram interpretation, examples of single phase and three phase voltage operated breakers

Specific Objectives

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

Cognitive Domain:

Define a voltage operated circuit breaker.
Explain the principle of operation of a voltage operated circuit breaker.
Interpret a schematic diagram of a voltage operated circuit breaker.
List examples of single phase and three phase voltage operated circuit breakers.

Affective Domain:

Appreciate the importance of circuit breakers in electrical safety.
Show interest in the study of electrical protection devices.

Psychomotor Domain:

Sketch a simple schematic diagram of a voltage operated circuit breaker.

Participate in discussions about electrical safety.

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 by T. F. Olaniyan.
https://www.electricaltechnology.org/2020/07/voltage-operated-circuit-breaker.html
https://www.powerelectronics.com/technologies/passive-components/article/21798319/the-voltage-operated-earthleakage-circuit-breaker

Instructional Materials

The teacher will teach this lesson with the aid of:

Single phase voltage operated circuit breaker.
Three phase voltage operated circuit breaker.
Charts showing schematic diagrams of voltage operated circuit breakers.

Rationale for the Lesson

This lesson helps pupils understand how a voltage operated circuit breaker protects electrical installations and users from faults. It enables them to recognize and apply essential safety principles in electrical work, which is important for preventing accidents and ensuring equipment longevity.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of electrical circuits, voltage, and the concept of electrical safety from previous lessons.

Lesson Content/Board Summary

INTRODUCTION TO VOLTAGE OPERATED CIRCUIT BREAKER

Meaning of Voltage Operated Circuit Breaker (VOCB)

A Voltage Operated Circuit Breaker (VOCB) is an electrical safety device designed to detect dangerous voltage levels between an earthed metal casing of an appliance and the local earth. When this voltage exceeds a predetermined safe limit, the VOCB automatically trips, disconnecting the power supply to prevent electric shock.

Principle of Operation of Voltage Operated Circuit Breaker

The principle of operation involves monitoring the voltage difference between the metal casing of an appliance and the earth terminal. If a fault occurs, such as a live wire touching the appliance casing, a voltage will develop across the coil of the VOCB. When this voltage reaches a dangerous level (typically 50V), it energizes a trip coil, which then mechanically opens the circuit, cutting off power. This action prevents a person from receiving an electric shock if they touch the faulty appliance.

Schematic Diagram Interpretation

A schematic diagram for a VOCB typically shows:

The main circuit conductors.
A sensing coil connected between the appliance’s metal casing and the earth.
A tripping mechanism that disconnects the main power supply when the voltage across the sensing coil exceeds a set value.
Test button for periodic verification of its operation.

Examples of Voltage Operated Circuit Breakers

Voltage operated circuit breakers are available for different power supply configurations. The following are common examples:

Single Phase Voltage Operated Circuit Breaker: Used in residential and small commercial installations where single-phase power supply is common.
Three Phase Voltage Operated Circuit Breaker: Employed in larger industrial and commercial settings that utilize three-phase power systems for heavy machinery and equipment.

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, takes attendance, reviews the previous lesson on basic circuit protection devices, and then introduces the topic “Introduction to Voltage Operated Circuit Breaker” by asking pupils about the importance of electrical safety.
Pupils’ Activity: Pupils respond to greetings, answer questions, and pay attention to the new topic.
Learning Point: Pupils recall previous knowledge and are prepared for the new lesson.

Step 2: Meaning of Voltage Operated Circuit Breaker

Time: 10 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines a voltage operated circuit breaker, explaining its purpose as an electrical safety device. The teacher displays a single-phase voltage operated circuit breaker and a three-phase voltage operated circuit breaker.
Pupils’ Activity: Pupils listen, observe the displayed devices, and ask questions for clarification.
Learning Point: Pupils understand the definition and general function of a VOCB.

Step 3: Principle of Operation of Voltage Operated Circuit Breaker

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the principle of operation of a VOCB, describing how it detects voltage differences between an appliance casing and earth. The teacher uses a chart or sketches a simplified schematic diagram on the board to illustrate the process.
Pupils’ Activity: Pupils observe the diagram, listen to the explanation, and try to explain the principle in simple terms.
Learning Point: Pupils grasp how a VOCB detects faults and disconnects power.

Step 4: Schematic Diagram Interpretation

Time: 5 minutes
Teaching Skill: Illustration/Interpretation
Teacher’s Activity: The teacher elaborates on the schematic diagram, pointing out key components such as the sensing coil, trip coil, and main contacts. The teacher explains what each symbol represents in the context of the VOCB’s operation.
Pupils’ Activity: Pupils observe the diagram carefully and identify the components as explained by the teacher.
Learning Point: Pupils learn to interpret the basic elements of a VOCB schematic diagram.

Step 5: Examples of Voltage Operated Circuit Breakers

Time: 5 minutes
Teaching Skill: Listing/Categorization
Teacher’s Activity: The teacher provides examples of voltage operated circuit breakers, differentiating between single phase and three phase types and mentioning their typical applications.
Pupils’ Activity: Pupils listen and note down the examples and their applications.
Learning Point: Pupils can identify and differentiate between types of VOCBs.

Step 6: Class Discussion/Activity

Time: 5 minutes
Teaching Skill: Questioning/Facilitation
Teacher’s Activity: The teacher engages pupils in a short discussion by asking questions like: “Why is it important to use VOCBs in homes and industries?” or “What might happen if a VOCB is not installed where needed?”
Pupils’ Activity: Pupils contribute their ideas and participate in the discussion.
Learning Point: Pupils reinforce their understanding and apply the lesson concepts.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Define a Voltage Operated Circuit Breaker.
Explain the principle of operation of a VOCB.
Mention two key components found in a VOCB schematic diagram.
List two examples of voltage operated circuit breakers.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: Immediately after Evaluation
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the role of VOCBs in electrical safety. The teacher then assigns homework, asking pupils to draw a simple schematic diagram of a VOCB and label its parts.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their learning and have an assignment to practice.

Lesson Keywords

Circuit Breaker – An automatic electrical switch designed to protect an electrical circuit from damage caused by an overload or short circuit.
Voltage Operated – Refers to a device that operates based on a specific voltage level or difference.
Earth Fault – An unintentional electrical path between an energized conductor and the Earth.
Trip Coil – A coil within a circuit breaker that, when energized, causes the breaker to open and interrupt the circuit.
Schematic Diagram – A diagram that represents the elements of a system using abstract, graphic symbols rather than realistic pictures.

Differentiation

The teacher will provide additional support for struggling learners through simplified explanations and one-on-one guidance, while advanced learners will be challenged with more complex questions and encouraged to research real-world applications of VOCBs.

Note for teachers using this lesson plan

Teachers should ensure that the actual voltage operated circuit breakers displayed are safe to handle and that any demonstration of a schematic diagram is clear and easy for pupils to follow. Emphasize the practical safety implications of understanding these devices.