Basic Electricity - Senior Secondary 3 - Protective devices

TERM: 1^ST TERM

WEEK EIGHT

Class: Senior Secondary School 3

Age: 17 years

Duration: 40 minutes of 5 periods each

Date:

Subject: BASIC ELECTRICITY

Topic: PROTECTIVE DEVICES

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

I.) Define protective devices

II.) Discuss the need for Protective Devices in Electrical Installations

III.) Identify the types and Uses of Various Protective Devices

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

NOTE

PROTECTIVE DEVICES

Protective devices are components or systems designed to safeguard electrical installations, equipment, and personnel from various hazards, including electric shock, overcurrents, overvoltages, short circuits, and earth faults. These devices play a critical role in ensuring the safety, reliability, and functionality of electrical systems by detecting abnormal conditions and taking corrective actions to prevent damage or injury.

Need for Protective Devices in Electrical Installations

1. Safety: Protective devices protect individuals from electric shock and related injuries by disconnecting power in the event of a fault or hazardous condition.
2. Equipment Protection: They safeguard electrical equipment and appliances from damage caused by overloads, short circuits, and voltage surges, thereby extending their lifespan and reliability.
3. Fire Prevention: Protective devices help prevent electrical fires by interrupting fault currents and isolating faulty circuits before they can escalate into hazardous conditions.
4. System Reliability: By promptly detecting and mitigating faults, protective devices help maintain the integrity and continuity of electrical systems, minimizing downtime and disruptions to operations.

Types and Uses of Various Protective Devices

1. Circuit Breakers: Circuit breakers are automatic switches designed to protect electrical circuits from overcurrents, short circuits, and earth faults.

Uses

   - They interrupt the flow of current when a fault occurs, thereby isolating the faulty circuit and preventing damage to equipment and wiring.

   - Types include miniature circuit breakers (MCBs), molded case circuit breakers (MCCBs), and residual current circuit breakers (RCCBs).

2. Fuses: Fuses are protective devices that contain a metal wire or element that melts when subjected to excessive current, interrupting the circuit.

Uses

   - They provide protection against overcurrents and short circuits by sacrificing themselves to prevent damage to downstream equipment.

   - Types include cartridge fuses, blade fuses, and thermal fuses.

3. Residual Current Devices (RCDs): RCDs, also known as ground fault circuit interrupters (GFCIs), detect imbalances in current between live and neutral conductors, indicating leakage to earth.

Uses

   - They trip the circuit if a fault current exceeds a predetermined threshold, protecting against electric shock and earth faults.

   - Common types include fixed RCDs for permanent installations and portable RCDs for temporary use.

4. Surge Protectors: Surge protectors, or surge suppressors, protect electrical devices and equipment from voltage surges or transient overvoltages caused by lightning strikes, switching events, or grid disturbances.

Uses

   - They divert excess voltage to the ground or absorb it through suppression components, preventing damage to sensitive electronics.

EVALUATION: 1. What are protective devices?

2. State 5 needs for Protective Devices in Electrical Installations
3. Indicate the uses the following devices: I. Circuit breaker II. Residual current devices

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively