Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Safely wire a single-phase circuit with protective devices.
• Diagnose and rectify common circuit faults.
• Connect and test a basic motor control circuit.
• Demonstrate understanding of safety protocols like lock-out/tag-out.
• Apply relevant SANS 10142 regulations.

Lesson summary

This week marks a crucial stage in your Grade 12 Electrical Technology journey. We're shifting our focus entirely to preparing you for the practical assessment tasks that form a significant portion of your final mark. Remember, Electrical Technology isn't just about theoretical knowledge; it's about applying that knowledge to solve real-world problems safely and effectively. In South Africa, the demand for skilled electricians is constantly growing, driven by infrastructure development, renewable energy projects, and the need for reliable power in homes and businesses. Your performance in these practical assessments will directly reflect your preparedness for a career in this vital sector.

Lesson notes

This section will cover critical concepts directly relevant to your practical assessments. 2.

1. Single-Phase Circuits and Wiring Regulations (SANS 10142)

Understanding Single-Phase Power: Single-phase power is the most common type of electrical power used in homes and small businesses in South Africa. It consists of a single alternating current (AC) voltage. Typically, in South Africa, this is 230V at 50Hz. Knowing the voltage is critical for selecting appropriate components.

SANS 10142 (Wiring Regulations): This is THE most important document for any electrician working in South Africa. It sets out the standards for safe and compliant electrical installations. Familiarize yourself with sections relating to circuit protection, earthing, bonding, and cable sizing.

Example: Regulation 6.1.6.1 requires that all circuits supplying socket outlets shall be protected by a residual current device (RCD) or earth leakage protection (ELP) with a rated tripping current not exceeding 30m

A. This is crucial for preventing electrocution. Live, Neutral, and Earth Conductors: Be absolutely sure you can identify these. The live conductor (typically brown) carries the current to the load. The neutral conductor (typically blue) completes the circuit. The earth conductor (typically green/yellow) provides a path to ground in case of a fault, preventing electric shock.

Cable Sizing: Cable size is determined by the current it needs to carry and the installation method (e.g., clipped direct, in conduit). Undersized cables can overheat and cause fires. Refer to cable rating tables (found in SANS 10142 or manufacturers' data) to select the correct cable size. Factors like ambient temperature and grouping of cables also affect the current carrying capacity and must be taken into account.

Example: You need to supply a 10A load with a cable installed clipped direct. Consulting a cable rating table, you might find that a 1.5mm² copper cable is sufficient.

However, if the ambient temperature is high, or the cable is grouped with other cables, you may need to increase the cable size. Protective Devices (MCBs and Earth Leakage Units): Miniature Circuit Breakers (MCBs): MCBs protect circuits from overcurrents (overloads and short circuits). They trip when the current exceeds their rated value, preventing damage to wiring and equipment. Different types of MCBs (B, C, D) have different tripping characteristics. B-type MCBs are generally used for resistive loads, C-type for inductive loads (like motors), and D-type for highly inductive loads.

Earth Leakage Protection (ELU/RCD): ELUs protect against electric shock by detecting small leakage currents to earth. They trip very quickly (typically within 30ms) when an earth fault is detected. 2.

2. Fault Finding and Troubleshooting Safety First: ALWAYS isolate the circuit before attempting any fault finding. Use a voltage tester to confirm that the circuit is dead. Apply lock-out/tag-out procedures.

Common Faults: Open Circuit: A break in the circuit, preventing current flow. Use a continuity tester to check for continuity between points in the circuit.

Short Circuit: An unintended connection between the live and neutral conductors, resulting in a high current flow. Often trips the MCB immediately. Visually inspect for damaged insulation or loose connections.

Earth Fault: A connection between the live conductor and the earth conductor. This can be caused by damaged insulation or faulty equipment. The ELU should trip immediately.

Using a Multimeter: The multimeter is your primary tool for fault finding.

Voltage Measurement: Use the voltage setting to check for the presence of voltage in different parts of the circuit.

Current Measurement: Use the current setting to measure the current flowing in the circuit.

Resistance Measurement: Use the resistance setting to measure the resistance of components and wiring. This is useful for identifying open circuits and short circuits. Continuity testing uses the resistance setting. 2.

3. Basic Motor Control (Direct-On-Line Starter)

Direct-On-Line (DOL)

Starter: The simplest type of motor starter. It connects the motor directly to the supply voltage. It consists of a contactor, an overload relay, and start/stop buttons.

Contactor: An electrically controlled switch that connects the motor to the supply.

Overload Relay: Protects the motor from overload conditions (e.g., excessive load on the motor). It trips when the motor current exceeds a set value for a certain period.

Start/Stop Buttons: The start button energizes the contactor coil, closing the contacts and connecting the motor to the supply. The stop button de-energizes the contactor coil, opening the contacts and disconnecting the motor.

Holding Circuit: A holding circuit (also called a latching circuit) is used to keep the contactor energized even after the start button is released. This is achieved by using a normally open auxiliary contact on the contactor in parallel with the start button. 2.4.