Selection, isolation, and earthing arrangements

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18th Edition

  Posted by: electrical-poster      11th August 2017

As the public consultation phase of 18th Edition of the Wiring Regulations Standard BS 7671 review draws to a conclusion on August 24th, Paul Collins, technical and training manager, Hager, highlights three important areas that could be subject to change from January 2019.

The Draft for Public Comment on the 18th Edition of the Wiring Regulations has been published and highlights a number of potential changes to the existing regulations. The document does though remain a draft at this stage and is subject to further change, revision and amendment.

Examination of the potential revisions outlines changes in three important areas such as selection and erection of equipment; protection, isolation, switching, control and monitoring and earthing arrangements.

Part 5: Selection & erection of equipment
For a number of years the regulations have stated that switchgear, protective devices, accessories and other equipment shall not be connected to a conductor intended to operate at a temperature exceeding 700C (unless the manufacturer can confirm that the equipment is suitable for such temperatures).

In the review, Note 4 has been added to 512.1.5 stating specifically that where this is the case tables 4D1A to 4D5 or tables 4H1 to 4H4 shall be used and tables 4E1 to 4E4A and tables 4J1 to 4J4 shall not be used when using 900C thermosetting cables.

In addition, 521.11 Wiring systems in escape routes has been deleted and replaced with 521.10.202.

In summary, the new regulation is essentially the same. However, it now applies to all wiring systems whether or not they are in escape routes. Metal clips, saddles or ties will therefore be required when using non-metallic cable management systems.

Chapter 53: Protection, isolation, switching, control & monitoring
Chapter 53 has now been completely revised and some of the key requirements within the new chapter include the following:

  • Devices for protection against electric shock by automatic disconnection of supply shall also be suitable for isolation.
  • Automatic reclosing devices providing protection against electric shock shall only be used where that associated part has access restricted to skilled or instructed persons only. A warning notice shall be clearly displayed where this associated part is protected by such a device.
  • Different types of RCDs are described (ie type AC, Type A etc.) and the appropriate RCD must be selected.
  • Where class I enclosures are used with TT systems and RCDs are used to give protection against electric shock on outgoing circuits, double or reinforced insulation of all live conductors shall be used on the supply side of the RCD.
  • 536 – co-ordination of protective devices has been expanded upon and now covers other items of electrical equipment and not just protective devices. This amended section covers the selection of electrical devices in terms of:
  • o Short-circuit
    o Overload
    o Residual currents
    o Selectivity.

  • Chapter 53 now includes an informative annex which gives guidance on the selection of devices to perform a particular function and also guidance on how to consider selectivity.
  • Chapter 54: Earthing arrangements and protective conductors
    This chapter now includes an additional requirement for an earth electrode to be added to an installation further to any earthing facility provided by the distributor.

There is also the recommendation that foundation earthing should be used for new buildings.

Finally, there are also new regulations added to Chapter 54 to provide for the switching of a protective conductor should this be necessary when two sources of energy supply an installation.