16th Edition (reference only) – NOW superseded by the 17th Edition IEE Regulations.

chapter 5

chapter 6

  5.1 - The earthing principle 5.6 - Protective multiple earthing (PME)
  5.2 - Earthing Systems 5.7 - Earthed concentric wiring
  5.3 - Earth fault loop impedance 5.8 - Other protection methods
5.4 - Protective conductors 5.9 - Residual current devices (RCDs)
5.5 - Earth electrodes

5.10 - Combined functional and protective

5.8.1 - Class II equipment

Class H equipment has reinforced or double insulation. As well as the basic insulation for live parts, there is a second layer of insulation, either to prevent contact with exposed conductive parts or to make sure that there can never be any contact between such parts and live parts. The outer case of the equipment need not be made of insulating material; if protected by double insulation, a metal case will not present any danger. It must never be connected with earth, so connecting leads are two-core, having no protective conductor. The symbol for a double-insulated appliance is shown in {Fig 5.20}.

Fig 5.20 British Standard symbol for double insulation

To make sure that the double insulation is not impaired, it must not be pierced by conducting parts such as metal screws. Nor must insulating screws be used, because there is the possibility that they will be lost and will be replaced by metal screws. Any holes in the enclosure of a double Insulated appliance, such as those to allow ventilation, must be so small that fingers cannot reach live parts (IP2X protection). Class II equipment must be installed and fixed so that the double insulation will never be impaired, and so that metalwork of the equipment does not come into contact with the protective system of the main installation. Where the whole of an installation is comprised of Class II equipment, so that there is no protective system installed, the situation must be under proper supervision to make sure that no changes are made which will introduce earthed parts.


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Extracted from The Electricians Guide Fifth Edition
by John Whitfield

Published by EPA Press Click Here to order your Copy.

Click here for list of abbreviations