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Hager guide: Hager Junction Box Guide to the 17th Edition

  2009-03-26         admin         Advice » Consumer Units Advice
For more than one hundred years the Wiring Regulations have provided the rules which must be followed to make sure that the electrical installations are safe. The introduction of the 17th Edition of the Wiring Regulations on the 1st January 2008 has major implications for all Electrical Contractors, Designers and Consultants. All the installations designed starting from the 1st July 2008 must comply with this new set of Regulations.  There are regulations concerning the connection of conductors relating to lighting and power final circuits. Read more about the Junction Box guide to the 17th edition(from Hager):

The Building Regulations & the Electrical Equipment

Since 2005 the Building Regulations for England and Wales have made direct reference to Electrical Installations, increasing the influence on how Electrical Equipment is installed in buildings. The part P of the Building Regulations 2000 came into effect on 1st January 2005 and was further amended on 6th April 2006. This document states that the requirements will be met by adherence to the ‘Fundamental Principles’ for achieving safety given in the Wiring Regulations BS 7671 Chapter 13.

For Scotland, the Building (Scotland) Regulations 2004 apply to domestic and non-domestic buildings. Section 4.5 Electrical Safety in the Scottish Building Standards Agency (SBSA) Technical Handbook prescribes that an electrical installation should be designed, constructed, installed and tested such that it is in accordance with the recommendations of the Wiring Regulations BS 7671. The ‘Fundamental Principles’ that are given in chapter 13 are intended to provide for the safety of persons, livestock and the protection of property against dangers and damage which may arise in the reasonable use of electrical installations.

Good workmanship by competent persons using the proper materials will reduce the risk of overheating or fire: It is recognised that good workmanship by competent persons using proper materials will reduce any hazards that may arise and that every item of equipment shall comply with the appropriate British Standard.

The electrical joints are a potential source of overheating and, if not securely made, could ultimately cause a fire. For this reason there are several regulations relating to electrical connections - these are mentioned in chapter 13 in regulation 134.1.4.

‘Every electrical joint and connection shall be of proper construction as regards conductance, insulation, mechanical strength and protection’.

Requirements of 17th Edition Wiring Regulations BS 7671: 2008

In this section we aim at explaining some of the regulations contained within the 17th Edition Wiring Regulations, regarding the connection of conductors both for lighting and power final circuits.

Electrical Connections

The requirements of the 17th Edition Wiring Regulations concerning electrical connections are covered mostly within section 526. This section states that every electrical connection shall have durable electrical continuity, adequate mechanical strength and protection.  The wiring method illustrated here is a common cause of non-compliance particularly with lighting circuits and the connections to downlighters in particular(see Hager J501, Hager 803 and Hager J804).

  • It can be seen that the sheath of the flex is not enclosed. This is due to the junction box connection method not facilitating an easy means of enclosing the outer sheath, a non-compliance with regulation 526.9.
  • Another problem is that during installation and maintenance, mechanical strain may be placed on the terminations of the conductors within the junction box. This is due to the lack of a clamping method for the cable, a non-compliance with the regulation 522.8.5.
Connections to downlighters are a common cause of non-compliance.
A further potential problem can be found within the junction box (opposite) concerning the type of conductors that are typically terminated. It is often the case in domestic installations that solid twin & cpc cables will be used for the fixed wiring with the conductor to the light fitting (or transformer if the lighting is ELV) being a flexible conductor.

Care must be taken to ensure the strands of the flexible cable are secured adequately in the terminal and have not been damaged to ensure compliance with regulation 526.2.

Also, as can be seen in the illustration on the left, when the conductor was removed for inspection it is clear that some of the strands have been damaged during termination.

Ensure that the connection method selected is fully compliant.

Downlighter Junction Box

When fitting recessed downlighters the following method would overcome all the issues raised previously.

It can be seen here that the sheath of both solid conductors and flexible conductors for the light fitting can be secured as they enter the enclosure. This enables compliance with regulation 522.8.5 in particular where it states that there shall be no undue mechanical strain on the terminations of the conductors. Also regulation 526.9, which requires the cores of sheathed cables from which the sheath has been removed to be enclosed, can be seen to be complied with(see Hager J501, Hager 803 and Hager J804).

Cable clamps prevent strain on terminations for compliance with regulations.
Regulation 526.2 is complied with where the method of connection shall take account of the number and shape of wires forming the conductor. In this junction box solid conductors and flexible conductors can be terminated separately by means of the unique three plate style terminal arrangement(see Hager J501, Hager 803 and Hager J804)..

Continue to read the Hager Junction Box guide to the 17th Edition, part 2.