A guide to the correct Junction Box

Junction boxes are an integral part of virtually every electrical installation. Unfortunately these connections often do not comply with the Wiring Regulations due to incorrect product selection.

We look at everyday snags using traditional junction boxes and solutions for compliance with the latest wiring regulations using Hager‘s range of maintenance free and downlighter junction box products.

Building Regulations

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. Indeed this is mentioned within 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’


Electrical Connections

The wiring method illustrated here is a common cause of non-compliance particularly with lighting circuits and the connections to downlighters in particular.

• 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 526.8.

• 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.

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 xed wiring with the conductor to the light tting (or transformer if the lighting is ELV) being a exible conductor. Care must be taken to ensure the strands of the exible 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 this illustration, when the conductor was removed for inspection it is clear that some of the strands have been damaged during termination.


Downlighter Junction Box

“Cable clamps prevent strain on terminations for compliance with regulations”.


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 exible conductors for the light tting 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 526.8, which requires the cores of sheathed cables from which the sheath has been removed to be enclosed, can be seen to be complied with.


Maintenance Free Connections

“Maintenance free terminals provide a solution where accessibility is an issue”.


Junction boxes are commonly used during alterations and additions to an installation.

Regulation 526.3 requires that every connection shall be accessible for inspection, testing and maintenance. There are 6 exceptions to this rule. Exception (vi) is:
“Equipment complying with BS 5733 for a maintenance free accessory and marked with the symbol and installed in accordance with the manufacturer’s instructions”.

BS 5733 de nes a maintenance free accessory as:
“An accessory which does not require further inspection, testing or maintenance after installation in a circuit, and which incorporates screwless terminals and cable clamps to secure any associated cables”.

The Electrical Safety Council Technical Manual states that “a junction box with screw terminals must be accessible”. This is to allow inspection of joints which could have relaxed or loosened over time, a potential problem with screwed terminals. So, unless provision is made for access, where boarding, carpet or other similar covering is laid over a junction box, it may not be considered accessible and maintenance free terminals should be used.

This is further reinforced in Appendix 15 of the Wiring Regulations which states “Junction boxes with screw terminals must be accessible for inspection, testing & maintenance or, alternatively, use maintenance-free terminals / connection (Regulation 526.3)”

Screwless terminals do not in themselves meet the requirements of regulation 526.3. Conformity is indicated by marking the symbol and BS 5733 on the maintenance free accessory.

BS 5733 prescribes additional requirements and tests for terminals for use within maintenance free accessories, to verify that:

  • Terminals have long-term connection capability
  • Terminals are resistant to the effects of vibration
  • Terminals withstand the effects of overloads and shall not cause ignition or damage to the mounting surface
  • Terminals are suf ciently resilient to the effects of thermal shock


Traditional Junction Boxes

“Junction boxes with screw terminals must be accessible for inspection”.


Unless using a solution such as maintenance free terminals, the access to electrical connections should be adequate for their safe and proper inspection, testing and maintenance. In this respect, connections should be in a location where they can reasonably be reached and where there is adequate working space.

Where connections are made in roof spaces and inter-floor spaces the enclosures containing the connections should normally be fixed and provision must be made for their access.

Providing these two constraints are complied with, then the continued use of standard circular junction boxes remains acceptable.


Article from Hager Technical Guides | www.hager.co.uk


1 Comment

  1. In all new or altered installation j b should not be used. As for lighting i.e. Spots cables should be installed to avoid j bs

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