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Requirements for extra low voltage ELV lighting installations Hager

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Requirements for extra low voltage ELV lighting installations Hager Powered By Docstoc
					                                                                                                • The transformer is short-circuit

             Requirements for
TECHNICAL


                                                                                                  proof (both inherently and
                                                                                                  non-inherently) and marked with
                                                                                                  the following symbol:
             extra-low voltage
             (ELV) lighting
             installations                                                                         Electronic convertors used for ELV
                                                                                                lighting installations must comply
                                                                                                with BS EN 61347-2-2 and be
                                                                                                marked with the following symbol:
             Extra-low voltage (ELV) lighting is commonly
             used in domestic and commercial installations,
             particularly in the form of recessed
             downlighter luminaires (see Figure 1)
                                                                                                Enclosure of connections
                                                                                                No less than for LV connections,
                                                                                                all connections (terminations and

            S
                   pecific requirements relating      an ELV luminaire does not have            joints) in (or to) an ELV lighting
                   to ELV lighting installations      a provision for connection of a           circuit must be enclosed in
            were newly introduced in BS 7671:         protective conductor, only a SELV         accordance with Regulation 526.5
            2008 in Regulation Group 559.11,          system may be used to supply the          to help prevent spread of possible
            as summarised in this article. The        luminaire (Regulation 559.11.2 refers).   fire should a loose connection
            article also includes information on         Safety isolation transformers          occur.
            the requirements for the enclosure of     used for ELV lighting installations          Many ELV luminaires are provided
            terminations and joints in ELV lighting   must comply with BS EN 61558-2-6          complete with an enclosure for
            installations and on methods to be        and meet with at least one of the         the connections between the
            employed for minimising the spread        following two requirements of             ELV circuit conductors and the
            of fire when installing downlighters.     Regulation 559.11.3.1.                    luminaire terminals. Figure 2
                                                      • The transformer is protected            shows an example of this where
            Shock protection measures                   on the primary side by a                the enclosure is separate from
            and supplies                                fail-safe protective device             the luminaire. Figure 3 shows an
            ELV supplies used for lighting should       that monitors the power                 example where the enclosure is
            be taken from a system meeting              demand of the luminaires and            attached to the luminaire.
            the requirements for the protective         automatically disconnects the              If a luminaire is provided without
            measures of SELV or PELV. It is not         supply in the event of one of           a suitable enclosure for the ELV
            permitted to use an FELV system             a number of specified fault or          connections, the installer must
            for an ELV lighting installation            failure conditions, as detailed in      provide an appropriate enclosure
            (Regulation 559.11.1 refers). Where         Regulation 559.11.4.2.                  complying with Regulation 526.5.




            1 A typical use of ELV lighting in commercial premises

        56 Spring 2009 NICEIC Connections                                                                            www.niceic.com
                                                                           Extra-low voltage
                                                                           luminaire terminals
                                                                       Transformer
                                                                Low voltage
                                                                joint box




                                                             Secure cable clamps
                                                             required at junction box entries




  Detail of low voltage junction box


2 Example of ELV luminaire with ELV connections in an enclosure separate from the luminaire




                                     Extra-low voltage
                                     luminaire terminals
                                  Transformer
                         Low voltage
                         joint box




     Secure cable clamps
     required at junction box entries




                                                                                                 Detail of luminaire ceiling entry

3 Example of an ELV luminaire with ELV connections in an enclosure attached to the luminaire
 Table 1: Minimum permitted cross-sectional area for ELV lighting circuit
                                                                                                 Wiring systems
 conductors
                                                                                                 Table 1, which is based on the
 General                                                                            1.5 mm2      requirements of Regulation 559.11.5.2,
 Flexible cables of a length not exceeding 3 m                                      1.0 mm2      gives the minimum permitted
 Suspended flexible cables or insulated conductors                                  4.0 mm2      cross-sectional area for the
                                                                                                 conductors of an ELV lighting circuit.
 Composite cables consisting of braided tinned copper outer                         4.0 mm2
                                                                                                 Larger conductor sizes may be
 sheath, having a material of high tensile strength inner core
                                                                                                 required in some cases, as explained
 Note: Larger conductor sizes may be required in some cases to meet the requirements of
                                                                                                 in the note to the table.
 Section 525 of BS 7671 for voltage drop (depending on the number of luminaires supplied and
 the length of run from the transformer) and Regulation Group 433.1 for co-ordination between
                                                                                                   It is not permitted to use metallic
 conductor and overload protective device.                                                       structural parts of the building or its



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TECHNICAL




            4 Part of a typical suspended ELV lighting system             5 Example of a downligher with integral fire protection

                                                       event of one of a number of          downlighters are exposed to a fire
                                                       specified fault or failure           from below, they may provide far
                                                       conditions, as detailed in           less fire protection to a ceiling and
                                                       Regulation 559.11.4.2.               the structural elements within it
                                                     • The system complies with             than the plasterboard that they
                                                       BS EN 60598-2-23 – Luminaires.       are replacing. It is recommended
                                                       Particular requirements.             that, wherever possible,
                                                       Extra-low voltage lighting systems   downlighters having integral
                                                       for filament lamps. Such a system    fire protection (see Figure 5) are
                                                       is constructed so that the           selected for use in all ceilings where
                                                       temperature of the conductors in     the lining to be penetrated is the
                                                       the output circuit does not rise     sole means of keeping fire and heat
                                                       by more than 10 ºC under short-      out of the cavity.
                                                       circuit conditions.                     Where integral fire protection is
            6 Example of a fire hood, for use           Where suspended bare conductors     not available owing to the design
            with a downlighter without integral      are used, at least one conductor and   or style of the luminaire, additional
            fire protection                          its terminals must be insulated for    fire protection may be fitted at
                                                     that part of the circuit between the   the time of installation in the
            services installations (such as          transformer and any short-circuit      form of a ‘fire hood’ (see Figure 6)
            pipes) or furniture as live conductors   protective device on the               or an insulated fire-protective box
            of an ELV lighting installation.         secondary side of the transformer.     or similar.
            Regulation 559.11.5.1 refers.            Regulation 559.11.5.3 refers.             Insulated fire-protective boxes, fire
                                                                                            hoods and the like must be fit for the
            Bare conductors                          Suspended systems                      purpose and not be easily dislodged
            If the nominal voltage does not          Where the ELV system is suspended      after installation by subsequent
            exceed 25 V a.c. or 60 V d.c., bare      (see Figure 4), the suspension         work. Guidance on selecting them is
            conductors may be used for ELV           device(s) must be capable of           given in Annex E of the Best Practice
            lighting, provided that                  supporting five times the weight       Guide mentioned at the end of
            • the installation is designed and       of the luminaire and its lamp, and     this article.
              installed or enclosed to reduce to a   not less than 5 kg. The suspended
              minimum the risk of a short-circuit,   system must be fixed to the walls by                             Further
            • the conductors have a                  insulated cleats and be accessible                               information
              cross-sectional area not less          throughout its length. Termination                               relating to
              than 4 mm2, and                        and connection methods must use                                  the impact
            • the conductors are not placed          either screw terminals or screwless                              of electrical
              directly on combustible material.      clamping devices, complying with                                 installations
               (Regulation 559.11.5.3 refers)        the appropriate standard. It is not                              on the fire
               Where both live conductors            permitted to use insulating piercing                             performance
            are uninsulated, one of the              connections and termination                                      of buildings
            following two requirements of            wires relying on counterweights to                               can be
            Regulation 559.11.4.1 must be met        maintain the electrical connection.                              found in the
            to reduce the risk of fire.              Regulation 559.11.6 refers.                                      Electrical
            • The conductors are provided with                                              Safety Council’s Best Practice Guide
              a fail-safe protective device that     Containing the spread of fire where    No5 Electrical installations and their
              monitors the power demand of           recessed downlighters are used         impact on fire performance of buildings,
              the luminaires and automatically       Unless suitable precautions            which is available as a free download
              disconnects the supply in the          have been taken, when recessed         at www.esc.org.uk




        58 Spring 2009 NICEIC Connections                                                                          www.niceic.com

				
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