Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain the purpose and scope of SANS 10142-1.
• Identify key requirements for cables, protection, and earthing.
• Apply SANS 10142-1 to select appropriate cables and protection.
• Describe earthing requirements for safety.
• Explain the role of the Certificate of Compliance (CoC).

Lesson summary

Industrial installations form the backbone of South Africa's economy, powering manufacturing plants, mines, and various industries. Understanding the regulations governing these installations is crucial for ensuring safety, efficiency, and compliance with legal requirements. As future electrical technicians and engineers, Grade 12 Electrical Technology learners need a solid grasp of these principles to contribute to a safer and more productive industrial environment. Incorrect or non-compliant installations can lead to severe consequences, including electrical hazards, equipment damage, production downtime, and legal penalties.

Lesson notes

2.1 Introduction to SANS 10142-1 SANS 10142-1 is the South African National Standard for the "Wiring of Premises Part 1: Low-voltage installations." It is based on international standards, primarily IEC 60364, but is adapted to suit South African conditions and regulations. It is published by the South African Bureau of Standards (SABS). It defines the minimum safety requirements for the electrical installation of buildings and premises operating at voltages up to 1000 V AC and 1500 V DC. This includes homes, offices and, critically, industrial premises. Why is SANS 10142-1 so important?

Legal Requirement: Compliance with SANS 10142-1 is generally mandated by the Electrical Installation Regulations issued under the Occupational Health and Safety Act (OHS Act) of

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3. This means that any electrical installation in South Africa must comply with its requirements.

Safety: The primary goal is to ensure the safety of people and property by minimizing the risk of electric shock, fire, and other electrical hazards.

Standardization: It provides a uniform standard for electrical installations, ensuring consistency and quality across the industry.

Insurance: Insurance companies often require compliance with SANS 10142-1 as a condition for providing coverage. 2.2 Key Definitions and Requirements Installation: The complete system of electrical equipment within a premises.

Final Circuit: A circuit connected directly to a point of utilization (e.g., socket outlet, light fitting, machine).

Overcurrent Protective Device (OCPD): A device (e.g., circuit breaker, fuse) designed to interrupt a circuit when the current exceeds a predetermined value.

Earth Leakage Protection: A system designed to detect and interrupt earth leakage currents, preventing electric shock.

Earth Electrode: A conductor or group of conductors buried in the earth to provide a connection to earth.

Bonding: The connection of metallic parts of an installation to earth to ensure equipotentiality and reduce the risk of electric shock.

Registered Person: An electrician registered with the Electrical Conformance Board of South Africa (ECB) who is authorized to issue a Certificate of Compliance (CoC). 2.3 Cable Selection SANS 10142-1 provides guidelines for selecting cables based on: Current-carrying capacity (Ampacity): The maximum current a cable can safely carry without exceeding its temperature rating. Cable ampacity is derated based on installation conditions, such as ambient temperature, grouping of cables, and burial depth. Tables in SANS 10142-1 specify ampacity for different cable types and installation methods.

Voltage Drop: The reduction in voltage along a cable due to its resistance. Excessive voltage drop can affect the performance of equipment. SANS 10142-1 specifies maximum permissible voltage drop limits (typically 5% for lighting and 5% for power circuits).

Short-circuit withstand: The ability of a cable to withstand the thermal and mechanical stresses caused by a short-circuit current.

Type of cable: Cables must be appropriate for the environment they are installed in (e.g. PVC, XLPE, SWA).

Example: A three-phase motor in a factory draws a full-load current of 40 A. The cable run is 50 meters. The ambient temperature is 35°C. The cable is installed in a cable tray with other cables. Select a suitable PVC insulated cable.

Determine the required cable ampacity: The cable ampacity must be greater than the full-load current. We need to apply derating factors for ambient temperature and grouping. Let's assume a derating factor of 0.8 for temperature and 0.85 for grouping. The required ampacity is 40 A / (0.8 * 0.85) = 58.8

A. Select a cable size from SANS 10142-1 tables: Referring to the cable ampacity tables, a 10mm² PVC insulated cable may be suitable, depending on the installation method, as it typically has an ampacity greater than 58.8A under standard conditions. Always consult the relevant tables in SANS 10142-

1. Calculate voltage drop: Calculate the voltage drop for the selected cable size. The voltage drop is calculated using the formula: VD = (√3 I L * R) / 1000 Where: VD is voltage drop (V), I is current (A), L is cable length (m), and R is resistance per meter (Ω/m). Assume the resistance per meter for a 10mm² PVC cable is 1.83 mΩ/m. VD = (√3 40 A 50 m * 1.83 mΩ/m) / 1000 = 6.34 V. Percentage voltage drop = (6.34 V / 400 V) * 100 = 1.59%. (Assuming a 400V supply)

Verify voltage drop is within limits: The voltage drop is 1.59%, which is less than the permissible 5%.

Therefore, a 10mm² PVC insulated cable is suitable. Always verify against the voltage drop table in SANS 10142-

1. Consider short-circuit withstand: Verify that the selected cable can withstand the maximum prospective short-circuit current at the installation point. This requires knowing the fault level (available short circuit current) at the distribution board.