Level 3 Electrotechnical Qualification - Protection for Safety

Understand Requirements of Protection for Safety for Electrical Installations

LO 4.1: Identify Requirements within BS 7671

  • Identify the specific requirements of protection for safety within the scope of BS 7671, which serves as the benchmark for electrical installations in the UK, ensuring safety and performance standards are adhered to. The standard outlines necessary measures for protecting individuals, property, and livestock from electrical hazards through systematic design, installation, and maintenance protocols.

LO 4.2: Interpret Application within BS 7671

  • Interpret how these requirements apply to electrical installations within the scope of BS 7671. This includes key areas of focus such as:

    • Protection against electric shock: Utilizing effective insulation, barriers, and disconnection methods.

    • Protection against thermal effects: Ensuring that electrical components do not overheat and cause fires.

    • Protection against overcurrent: Implementing devices that prevent current overloads.

    • Protection against voltage disturbances and electromagnetic disturbances: Safeguarding circuits from unexpected surges.

    • Isolation and switching: Ensuring safe control over electrical systems for maintenance and emergencies.

Chapter 41 – Protection Against Electric Shock
General Principles

  • Based on BS EN 61140, considered the fundamental safety standard for protecting persons and livestock against a variety of electrical hazards.

  • Emphasizes two aspects of protection:

    • Under normal conditions: Basic protection against all foreseeable hazards.

    • Under single fault conditions: Fault protection to manage risks associated with equipment failures.

Types of Hazard

Protection must be systematically addressed against two distinct types of hazard:

  • Protection in use without a fault (basic protection): Safety measures that prevent contact with live current under normal operation.

  • Protection under fault conditions (fault protection): Measures to mitigate the dangers if a fault occurs, such as grounding and automatic disconnection.

410 – Protection Against Electric Shock
Fundamental Rule

  • Hazardous-live parts (exposed conductive parts that can become live) shall not be accessible.

  • Accessible conductive parts must not be hazardous-live which would pose electric shock risks.

  • This rule applies both in use without a fault and in single fault conditions, integrated through a combination of both basic protection and fault protection strategies.

Basic Protection

  • Relates to protection under normal, fault-free conditions, covered in Section 416 of BS 7671. Potential shock sources include:

    • Contact with a live part while simultaneously in contact with earth, which can lead to severe shock.

    • Contact with live parts that operate at different potentials, typically resulting in current flow through the body.

  • Basic protection is provided by:

    • Basic insulation of live parts to prevent accidental contact.

    • Barriers or enclosures in accordance with Section 416 to further isolate live parts from users.

Fault Protection

  • Defined as “protection against electric shock under single fault conditions.” Key protections include:

    • Protective earthing: Grounding of electrical systems for safety in the event of a fault.

    • Protective equipotential bonding: Ensuring all conductive parts are at the same electrical potential to minimize shock risks.

    • Automatic disconnection in case of a fault, in accordance with Regulations 411.3–6, which outlines strategies for quick disconnects to prevent injury.

Protective Measures

  • When assessing protection needs, external influences must be considered, including environmental factors that may affect safety. Generally accepted protective measures include:

    • Automatic disconnection of supply: Fundamental in preventing electric shocks.

    • Double or reinforced insulation: Used on appliances to enhance safety.

    • Electrical separation: Ensures that certain systems remain isolated from other potentially conflicting electrical systems.

    • Extra-low voltage: Use of SELV or PELV circuits to reduce electrocution risks in sensitive areas.

Combination of Provisions

  • Each protective measure usually comprises an:

    • Appropriate combination of provisions for basic protection and fault protection.

    • Enhanced protective provision that effectively delivers both basic protection and fault protection to maximize user safety.

Restrictions

  • The experiment with obstacles and securing equipment out of reach is permissible only in installations intended for skilled or instructed persons, such as fencing around high-voltage transformers.

  • Also, protective measures dictated in section 418, especially regarding earth-free equipotential bonding, should be enforced where skilled supervision is present.

  • Regulation 410.3.9 states that provisions for fault protection may be omitted in specific equipment scenarios, like metal supports for overhead line conductors, given they are secured beyond reach.

Non-Conducting Location

  • Defined as an area with insulated walls, floors, and ceilings, ensuring there are no protective conductors within such spaces, indicating a low-risk environment.

  • Socket outlets are required to have no earthing connections, further reducing the risk of electric shock.

Earth-Free Equipotential Zone

  • An area comparable to a Faraday cage, where all metallic elements are bonded together, creating a uniform electrical potential.

  • Caution is required during entry to such zones to avoid significant electrical potential differences.