BS 7671 and exterior lights

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The application of BS 7671 to exterior lighting

This article discusses the requirements of Section 714 and other regulations relating to exterior lighting; this will include equipment used to illuminate areas such as highway power supplies and street furniture.

In previous versions of BS 7671, outdoor lighting installations were included as part of Section 559 – Luminaires and lighting installations. However in Amendment 3, outdoor lighting installations are classifi ed as being a special installation and are now the subject of the additional requirements of Section 714. It should be remembered that, like the requirements of other special installations, the requirements of Section 714 supplement or modify the general requirements contained in Parts 1 to 6 of the regulations. Consequently, where a regulation is not supplemented or modifi ed by a regulation in Section 714, the requirements contained in parts 1 to 6 of BS 7671 will apply; for example, Regulation 559.5.3 dealing with through wiring is applicable to outdoor lighting installations.

Section 714 applies only to specifi c types of outdoor lighting installations such as street electrical furniture, street lighting, road signs and lighting arrangements in telephone kiosks, bus shelters and the like. Section 714 specifi cally excludes any application to temporary festoon lighting, luminaires fi xed to the outside of buildings supplied directly from the internal wiring of that building (refer Fig 1) and road traffi c signals (Regulation 714.1 refers).

Fig 1 An example of luminaires supplied

directly from the internal wiring of a building

Protective measures

Similar to other types of special locations, Regulation 714.410.3.6 prohibits the use of the protective measures non-conducting locations and earth-free local equipotential bonding for outdoor lighting installations.

Where the protective measure automatic disconnection of supply is used, Regulation 714.411.201 requires that all live parts of electrical equipment shall be protected by insulation or barriers or enclosures providing basic protection. Furthermore, Regulation 714.411.2.201 requires: • that unless the enclosure is in a location only accessible to skilled or instructed persons, the live parts of every accessible enclosure shall only be accessible with a key or a tool. It should be noted that this regulation applies to all enclosures forming part of the outdoor lighting installation and not just to luminaires • luminaires mounted at a height less than 2.8 m above ground level should be designed so that access to the light source shall only be possible aft er removing a barrier or an enclosure requiring the use of a tool • doors giving access to electrical equipment (such as lighting columns) and located less than 2.5 m above the ground shall be locked with a key or shall require the use of a tool for access. In addition, when the door is open, basic protection shall be provided by either the use of equipment having a degree of protection of IPXXB or IP2X or by installing a barrier or an enclosure giving the same degree of protection.

Except for circuits supplying fi xed equipment used in highway power supplies where a maximum disconnection time of 5 s is stated (Regulations 714.411.202 refers), Section 714 does not contain any specifi c requirement regarding maximum disconnection times. Consequently, where the protective measure is automatic disconnection of supply, the disconnection times given in Section 411 apply. This means, for example, that where a socket-outlet rated at

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Fig 2 Example of where RCD protection is required

where the cable is buried in the render of a wall

less than 32 A is used to supply garden lighting, the maximum disconnection time of 0.4 s would apply for a TN system and 0.2 s for a TT system (Regulation 411.3.2.2 refers).

Whilst there is no general additional requirement for all outdoor lighting installations to have additional protection by RCD, lighting in locations such as telephone kiosks and bus shelters does require additional protection by an RCD having characteristics specifi ed in Regulations 415.1.1 (Regulation 714.411.3.3 refers). Furthermore, an RCD may be required where: • the luminaire is connected to the supply via a plug and socket-outlet, or • the external lighting is installed on a rendered wall with the cables buried less than 50 mm from the surface (refer Fig 2) and the requirements of Regulation 522.6.202 apply. In this situation where the method of installation is other than those described in Regulation 522.6.204 the cables should be installed in zones and additional protection by means of a RCD having the characteristics of Regulation 415.1.1 should be provided.

There is no requirement for all buried cables to have additional protection by RCD.

Being exposed to the full range of British weather, exterior lighting equipment will be subjected to a wide range of external infl uences including heat, water, corrosion, solar radiation and wind. In addition, depending on the location, the exterior lighting could be subject to impact and the eff ects of fl ora and fauna.

Regulation 714.512.2.105 requires that electrical equipment forming part of outdoor lighting installation shall, by construction or by installation, have a degree of protection of at least IP33. Furthermore, Regulation 714.512.2.1 recommends that the equipment should be suitable for a temperature range from -40 °C to +40 °C and be suitable for relative humidity between 5 % and 100 %. However, the degree of protection specifi ed is a minimum value and in locations where say hose pipes are used for washing vehicles, the degree of protection should be increased.

For luminaires fi xed to the outside of a building and supplied directly from the internal wiring of the building, being outside the scope of Section 714, the requirements for external infl uences is given by Regulation 512.2.1. This requires equipment to either be of a design appropriate to the situation in which it is to be used or its mode of installation shall take into account the conditions likely to be encountered. For luminaires supplied directly from internal wiring and fi xed to the outside of buildings a degree of protection of IP33 will generally satisfy the requirements of Regulation 512.2.1.

Regulation 714.537.2.1.1 requires that, except as described in Regulation 537.1.2, every circuit shall be capable of being isolated from each of the live supply conductors. Regulation 537.1.2 recognises, that in TN-S or TN-C-S systems, the neutral conductor is reliably connected to Earth, and need not be isolated. Consequently, outdoor lighting supplied by a single-phase TN-S or TN-C-S system can be isolated by a single-pole device in the line conductor but outdoor lighting supplied by a single-phase TT system should be isolated using a double-pole device.

Where the isolation and switching is to be carried out only by instructed persons, and then only for TN systems and providing suitable precautions are taken, Regulation 714.537.2.1.201 permits a suitably rated fuse carrier to be used as a means of isolation and switching.

Where ground-recessed luminaires form part of an exterior lighting scheme, Regulation 714.512.3 requires that the selection and erection shall take into account the guidance given in Table A.1 of BS EN 60598-2-13. This standard deals with particular requirements of ground recessed luminaires and Annex A of the standard provides a guide to good installation practice. Included in Annex A is Table A.1 which, for various locations where the ground recessed luminaires could be installed, provides details of temperature limits, dimensions and resistance to static loads.