Amendment 1 Diary (July)

In the third article on the first amendment to the 17th Edition Wiring Regulations, George Murphy of AMTECH Power Software continues to identify the main changes, which have now been published. This was also published in the June issue of the Electrical Times magazine

In previous articles we have looked at a number of key changes to the 17th Edition Wiring Regulations (BS 7671) – which have now been confirmed in the published version of Amendment 1. In this article we will focus on the changes in Parts 5, 6 and 7.

In Part 5 the main change is the new Section 534, which introduces ‘devices for protection against overvoltage’. A transient overvoltage is a significantly higher voltage than normal, typically introduced by direct or indirect lightning strike or switching of large inductive loads. These overvoltages may only last for micro-seconds but can be as high as 6kV and cause severe damage.

Three types of surge protective devices are mentioned in BS 7671. Type 1 usually installed at the main distribution board, Type 2 installed at sub-main boards and Type 3 installed in close proximity to the equipment it protects.

Changes in Part 6 are minimal, with the term Periodic Inspection Report being replaced by an Electrical Installation Condition Report – the main changes relating to inspection and testing are in Appendix  6.

This new report uses more meaningful classification codes for recorded observations. Code 1 identifies a present danger and requires immediate action to make the system safe – or make the responsible person aware with a written notification as a matter of urgency.

Schedules of inspection are now dependant upon the size of the installation.  A schedule of inspection is provided in Appendix 6 for installations with a supply rating not exceeding 100A. For installations where demand exceeds 100A a comprehensive but not exhaustive list of items requiring inspection has been provided. The layout of the schedule should be clarified when GN 3 is published in October.

Part 7, covering special installations, sees two new sections; Section 710 – Medical Locations and Section 729 – Operating or Maintenance Gangways.

For medical locations, the nature of the risk to patients or staff has to be decided and installation safety requirements must be appropriate. Risk levels are defined as Group 0, Group 1 or Group 2 – the latter being where a loss of supply could result in a danger to life.

Disconnection times for areas defined as Group 1 or 2 have been reduced to 0.3 seconds on TN systems and 0.05s on TT systems.

Section 729 – Operating or Maintenance Gangways – applies to basic protection when work has to be carried out during the operation or maintenance of switchgear and control gear within restricted areas including gangways. Where access to areas is restricted, this shall be clearly and visibly marked by appropriate signs, and access to unauthorized persons shall not allowed. Any doors should allow easy evacuation.