17th Edition IEE Wiring Regulations

BS 7671 (The IEE Wiring Regulations) are the national standard to which all domestic and industrial wiring must conform. The 17th edition contains substantial changes to align with European documents.

The Regulations apply to the design, installation and testing of electrical installations, also additions and alterations to existing installations.

Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading.

Key Changes 

RCD Protection to Socket Outlets 

  • Socket outlets rated not exceeding 20 A and intended for general use by ordinary persons must be protected with 30 mA RCDs(Residual Current Devices). This means that general purpose sockets in domestic and similar properties must have RCD protection. An exception can be made for socket outlets for specific purposes eg domestic freezer circuit, this socket should be suitably labelled or otherwise identified.
  • External sockets rated not exceeding 32 A must also have 30 mA RCD protection.

Installation of cables – RCD Protection Requirements

  • Cables that are buried less than 50mm into a wall or partition and are not enclosed in earthed metallic covering or have mechanical protection capable of resisting nails or screws should be protected by a 30 mA RCD as well as being installed in the ‘safe zones’ as previously permitted.
  • Similarly, irrespective of depth of cable, cables that are installed in metal framed walls require 30 mA RCD protection if not otherwise protected by earthed metallic covering.

The above requirements do not apply to installations where the installation is intended to be under the supervision of a skilled or instructed person, such as in office buildings, large retail outlets and industrial premises.

Bath/ Shower Rooms (containing a fixed bath or shower) 

Bathroom and Wet Room Zones
  • All circuits within a bathroom must have RCD (30mA) protection. Where this is provided and main equipotential bonding is used in the installation then supplementary equipotential bonding is not required.
  • Bathrooms being modified or refurbished can either have their supplementary equipotential bonding extended or can be rewired with the installation of RCDs.
  • Zone 3 has been removed
  • 13A sockets in bathrooms are allowed providing they are installed at least 3m from the edge of the bath and protected by a 30mA RCD.

Under Floor Heating Systems

Underfloor and ceiling heating systems are now covered as a special location/installation.

  • A plan of the heating system shall be provided for each system (showing location, area, rating details, descriptions for use etc). A copy of the instructions for use should be fixed adjacent to the distribution board supplying the heating.
  • Heating systems which do not have an exposed conductive covering or mesh must have installed on site a suitable exposed conductive part installed above the heating element. This could be in the form of an earthed metallic grid with spacing of not more than 30mm.
  • A 30mA RCD must be used as the disconnection device.
  • Heating systems of Class II (Double insulated) construction shall be provided with 30mA RCD protection.
  • Floor heating systems in bathrooms the metal sheath, metal enclosure or fine mesh metallic grid should be connected to the protective conductor of the supply circuit.

Maximum Zs values

  • There are new values based upon a nominal voltage of 230v and not 240v hence the values have been slightly reduced (i.e. 32A Type B MCB was 1.50 now 1.44).

A new table has been provided giving the maximum values of earth fault loop impedance for RCDs.

Voltage Drop

  • The new regulations now provide different voltage drop values for installation supplied from a public supply and private supply (i.e. Own generation). For a public supply the maximum values are 3% for lighting and 5% for other uses, for a private supply the maximum values are 6% for lighting & 8% for other uses.

Disconnection Times

  • Final circuits not exceeding 32A shall have a maximum disconnection of 0.4 seconds for a TN-S or TN-C-S (PME) earthing arrangements.
  • For TT systems the maximum disconnection time is 0.2 seconds, however a statement is included in the table (41.1) which states “Where disconnection is achieved by an overcurrent protective device, and the protective equipotential bonding, or main equipotential bonding, is correctly installed, the maximum disconnection times applicable to a TN system may be used.”

New Sections on: 

  • 559 – Luminaries and Lighting
  • 709 – Marinas and similar locations
  • 711 – Exhibitions, Shows and Stands
  • 712 – Solar Photovoltaic (PV) Power Supply Systems
  • 717 – Mobile or Transportable Units
  • 721 – Caravans and Motor Caravans
  • 740 – Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses