Chapter 13 – Fundamental Principles

Topic Progress:

Although the regulations relating to Protection for Safety are detailed in Part 4, this chapter, Chapter 13 states the fundamental principles relating to protection for safety, design, selection, erection and verification of electrical installations. All the principles covered in this chapter will be repeated at relevant sections later on. This duplication matches the duplication in the Regulations.

Chapter 13 is a broad but very crucial chapter to for an electrician to know and every part, while not specific, should be fully understood; it is the foundation for all other requirements.

However, when sitting the 2382 exam, do NOT rely on referencing Chapter 13. In nearly all cases, the questions you will be asked require you to refer to the regulations in the detailed Parts and Chapters.

Chapter 13 and BS7671 in general, exists to provide for the safety of persons, livestock and property against dangers and damage which may arise in the reasonable use of electrical installations.

131.1 General – Risk of injury

Risk of injury can arise from:

  1. Shock currents
    A person or livestock can be protected against shock by direct contact, by limiting the current which can pass through a body to a non-hazardous value.
    Fault protection can also protect against shock by limiting the magnitude of a current to a non-hazardous value, and by limiting the duration of the current to a non-hazardous time period. The method of equipotential bonding is an important principle for protection for safety. Note that the definition for ‘direct contact’ has been deleted by BS7671:2008 and is now covered by the ‘basic protection’ definition.
  2. Excessive temperatures likely to cause burns and fires
    To protect against thermal effects, the installation must be arranged that the risk of ignition of flammable materials is minimized. The factors of combustion, ignition, or degradation of materials, risk of burns, and impairment of the safe function of installed equipment should be taken into consideration.
  3. Ignition of potentially explosive atmosphere
  4. Undervoltages, overvoltages and electromagnetic influences likely to cause or result in injury or damage
    Personnel and livestock should be protected against effects of a fault between live parts of circuits supplied at different voltages and atmospheric events. In addition, protection must be provided for undervoltage and the subsequent recovery. When installed, there should be an adequate level of immunity against electromagnetic disturbances by taking into consideration electromagnetic emissions that the installation will produce.
  5. Mechanical movement of electrically actuated equipment therefore causing injury
  6. Power supply interruptions of safety services
    When damage or danger is expected to arise due to an interruption of supply, suitable provisions shall be made in the installation or installed equipment.
  7. Arcing, likely to cause blinding effects, excessive pressure, and/or toxic gases

132 Installation Design

The installation should be designed for the protection of persons, livestock and property and for the proper functioning of the installation for intended use.

The following characteristics should be included in the documentation to show conformity with the Regulations. This section has been the source of exam questions.

  • Nature of current (AC / DC)
  • Purpose and number of conductors:
  • For AC: Line conductors, neutral conductors, protective conductor, PEN conductors
  • For DC: Conductors equivalent to those listed above (outer/middle/earthed live conductors, protective conductor, PEN conductor)
  • Values and tolerances:
  • Nominal voltage and voltage tolerances
  • Nominal frequency and frequency tolerances
  • Maximum current allowable
  • Earth-fault loop impedance
  • Protective measures inherent in the supply (earthed neutral of mid-wire)
  • Particular requirements of the distributor.
  • The nature of the demand should be determined from knowledge of:
  • Location of points of power demand
  • Loads to be expected on the various circuits
  • Daily and yearly variation of the demand
  • Harmonics and any other special conditions
  • Anticipated future demand
  • Requirements for control, signalling, communication and information technology
  • If a supply for safety services is specified, the following should be determined:
  • Source of supply
  • Circuits to be supplied by the electrical source for safety services or the standby electrical source

Equipment exposed to the environment should be protected to prevent dangerous conditions.

The cross-sectional area of conductors, the type of wiring and method of installation, and protective equipment should all be factors in the design with respect to both normal current loads and fault current loads.

If a possibility of danger exists that would require immediate interruption of the supply of power, an interrupting device should be installed. Accessibility should be a factor for installation and repair, as well as disconnecting devices. All documentation should be supplied with the electrical device upon installation.

A single-pole fuse, switch or circuit breaker shall be inserted in the line conductor only. NEVER should a switch, fuse or circuit breaker be inserted in an earthed neutral conductor.

When selecting electrical equipment, compliance with the appropriate British Standard is mandatory. In addition, the voltage, current, frequency and power should all comply with the circuit’s needs and capacities.

At all times, good workmanship by skilled persons and proper materials should be used in the erection of the electrical installation. When the installation is complete, a qualified individual should inspect and verify the installation’s completion. They should also make a recommendation for subsequent periodic inspection and testing.

133 Selection of equipment

133.1.1 – Every item of equipment shall comply with the appropriate British or Harmonized Standard. In the absence of such a standard, reference shall be made to the appropriate International (IEC) standard or the appropriate standard of another country.

133.1.3 – Where equipment to be used is not in accordance with Regulation 133.1.1 or is used outside the scope of its standard, the designer or other person responsible for specifying the installation shall confirm that the equipment provides at least the same degree of safety as that afforded by compliance with the Regulations. Such use is to be noted on the Electrical Installation Certificate specified in Part 6.

This requirement for including a note in the EIC is new for the 18th Edition.

 


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