Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Identify key components of industrial electrical installations.
• Describe the purpose of SANS 10142-1 regulations.
• Understand basic calculations for cable and protective device selection.
• Explain the importance of inspection and testing.
• Differentiate between electrical hazards and safety measures.

Lesson summary

Industrial installations represent a significant area of electrical technology, particularly in South Africa's thriving industrial sector. Understanding the regulations governing these installations is crucial for ensuring safety, efficiency, and compliance. Improperly installed or maintained electrical systems in factories, mines, and other industrial settings can lead to devastating consequences, including electrical shocks, fires, equipment damage, and production downtime, all of which negatively impact our economy and community safety. This week’s focus aims to equip you with the foundational knowledge to understand these complex systems and regulations.

Lesson notes

2.1 Key Components of an Industrial Electrical Installation An industrial electrical installation typically consists of several interconnected components that work together to safely and efficiently distribute electrical power throughout the facility.

Incoming Supply: This is the point where electrical power enters the industrial facility, usually from Eskom (South Africa's national electricity provider). It includes the main switchgear, which serves as the primary control and protection point for the entire installation. High voltage supplies are stepped down using transformers, often housed in separate substations within the facility or on the property.

Transformers: Transformers are essential for stepping down high voltage electricity from the supply network (e.g., 11kV or 33kV) to a lower voltage suitable for industrial use (e.g., 400V or 525V). Three-phase transformers are standard in industrial settings.

Main Distribution Board (MDB): The MDB receives power from the incoming supply (after transformation) and distributes it to various sub-distribution boards (SDBs) located throughout the facility. It houses main circuit breakers, metering equipment, and other control devices.

Sub-Distribution Boards (SDB): SDBs further distribute power from the MDB to individual circuits feeding motors, lighting, machinery, and other electrical equipment. Each SDB contains circuit breakers or fuses to protect these individual circuits.

Protective Devices: These devices are critical for protecting the electrical system and personnel from overcurrents, short circuits, and earth faults.

Common protective devices include: Circuit Breakers:* Automatically interrupt the circuit when an overcurrent or short circuit is detected. They can be reset after the fault is cleared.

Fuses:* Melt and break the circuit when subjected to an overcurrent. They need to be replaced after they blow. Earth Leakage Circuit Breakers (ELCBs) / Residual Current Devices (RCDs):* Detect earth leakage currents (current flowing to earth due to insulation failure) and quickly trip the circuit, preventing electric shock. They are mandated in many industrial applications, especially in damp or wet environments.

Cables and Wiring: Conductors that carry electrical current throughout the installation. Proper cable sizing is crucial to prevent overheating and voltage drop. Industrial installations often utilize armored cables (e.g., SWA – Steel Wire Armoured) for mechanical protection.

Earthing System: A properly designed and installed earthing system is essential for safety. It provides a low-impedance path for fault currents to flow back to the source, allowing protective devices to quickly trip and clear the fault. The earthing system includes earth electrodes (buried in the ground), earth conductors, and bonding conductors. 2.2 SANS 10142-1: The Wiring of Premises SANS 10142-1 is the South African National Standard that governs the wiring of premises, including industrial installations. It specifies requirements for design, installation, inspection, testing, and maintenance of electrical installations to ensure safety and prevent hazards. Key aspects covered by SANS 10142-1 include: Cable Selection and Sizing: The standard provides guidelines for selecting appropriate cable types and sizes based on the current carrying capacity, voltage drop, installation method, and environmental conditions.

Protection Against Overcurrent: Specifies requirements for the selection and coordination of overcurrent protective devices (circuit breakers and fuses) to protect conductors and equipment from damage due to overloads and short circuits.

Protection Against Earth Faults: Mandates the use of earth leakage protection (ELCBs/RCDs) in certain circuits and specifies requirements for earthing systems to ensure effective fault current path.

Wiring Methods: Specifies acceptable wiring methods for different types of installations, including conduit systems, cable trays, and direct burial.

Inspection and Testing: Requires regular inspection and testing of electrical installations to verify compliance with the standard and identify potential hazards. A Certificate of Compliance (CoC) is required after any new installation, repair, or alteration. 2.3 Cable Sizing Calculations Cable sizing involves determining the appropriate cross-sectional area of a cable to carry the intended current without overheating or experiencing excessive voltage drop.

The key factors to consider are: Rated Current (Ib): The maximum current that the circuit is expected to carry under normal operating conditions.

Cable Current-Carrying Capacity (Iz): The maximum current that the cable can safely carry without exceeding its temperature rating. This value is obtained from cable manufacturer's data or relevant tables in SANS 10142-1, and is dependent on the cable type, installation method (e.g., clipped direct, in conduit), and ambient temperature.