SHS2 Applied Technology · Semester 2 Week 9: Electrical Systems Design

Lesson notes

Learning Objectives

Indicator: 2.5.1.LI.5 - Describe how a circuit is protected against excess current

By the end of the lesson, learners can:

Define excess current and explain the two main causes of excess current in a circuit (overload and short circuit) with at least one example of each.
Explain the difference between close protection and coarse protection, giving the typical current rating range and purpose of each.
Differentiate between fuses and circuit breakers by comparing at least three features such as speed of operation, reusability, and cost.
Select an appropriate protective device for given final circuits (lighting 5A, socket outlet 20A, cooker 30A) and justify the choice based on the circuit’s expected current demand.
Outline two advantages and two disadvantages of fuses and two advantages and two disadvantages of circuit breakers.

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Curriculum details

Strand: Electrical and Electronic Technology (Strand 5)
Sub-strand: Electrical Systems Design (5.1)
Content standard: 2.5.1.CS.1 - 2.5.1.CS.1 Demonstrate understanding of House Wiring 2.5.1.LO.1 Apply appropriate tools and wiring systems to carry out key wiring processes.
Indicator: 2.5.1.LI.5 - Describe how a circuit is protected against Excess current
Suggested placement: Semester 2, Week 9 (Week 29 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Source document note: The official curriculum document has a fault in this entry, so the curriculum text above is transcribed exactly as printed:

indicator text - p.115: prints the learning-indicator code as "2.5.1.L1.5"
Curriculum reference: NaCCA curriculum document, p. 115

Exemplars (from the NaCCA curriculum)

Talk for learning/collaborative learning: In mixed-ability or mixed-gender groups, guide learners to undertake the following activities:
1. Explain excess current
2. Explain close and coarse protection
3. Differentiate between fuses and circuit breakers
4. Select appropriate Protective devices for various circuits eg 5A fuse for lighting. 30A fuse for cooker)
Problem-Based Learning: Work in pairs to: Determine protective devices for various circuits
1. Determine how to select an appropriate protective device for each final circuit e.g. for lighting system 5A, cooker control unit 30A, socket outlet 20A, teaching them to adhere strictly to rules and regulations governing house wiring.
2. Compare and contrast fuses and circuit breakers
3. Outline the advantages and disadvantages of fuses and circuit breakers.
4. Ensure all learners participate in all varieties of practical activities and project work given mixed gender groupings as well

Assessment (2.5.1.AS.5). The document marks these depth-of-knowledge levels for this indicator: Level 3 Strategic reasoning; Level 4 Extended critical thinking and reasoning.

Teaching and Learning Materials:
- Cables
- Trunkings
- conduit pipes
- accessories
- megger
- fittings
- multimeter