Ask the experts/Technical
Fully charged Fig 4 Automatic disconnection of supply used in conjunction with additional supplementary bonding and provision of a functional earthing conductor Access
Protective device
Fixed equipment (exposedconductive-part)
Source
extraneous-conductive-parts of the location, and the earthing terminal of the PELV supply to Earth. Sources for electrical separation Where the protective measure electrical separation is used, the source (typically a transformer with separate primary and secondary windings) should provide at least simple separation of the separated circuit from other circuits and from Earth, and be sited outside the location, unless the source forms a part of the fixed installation within the location. The winding supplying the electrically separated circuit must be unearthed. Regulation 706.413.1.2 refers. Particular requirements for SELV and PELV
cpc
Functional earthing conductor Fortuitous contact with earth
Extraneousconductive-part Additional supplementary bonding conductors
Regulation 706.413(ii) requires that the source for any SELV or PELV system is sited outside the location, as shown in Figs 3a and 3b, unless the source forms a part of the fixed installation within the location. Where either SELV or PELV is used in the location, Regulation 706.414.4.5 requires basic protection to be provided by either basic insulation in accordance with Section 416.1 or by barriers or enclosures in accordance with Section 416.2,regardless of the nominal voltage. Functional earthing
The protective measure of electrical separation in accordance with the requirements of Section 413 may also be used, with only a single item of equipment being connected to a secondary winding of the transformer. The transformer may have more than one secondary winding. Finally, protection may be provided by SELV, or by PELV if equipotential bonding is provided that connects together all exposed-conductive-parts (such as metallic conduits and equipment cases) and
Where it is necessary to provide functional earthing, such as could be necessary for certain electronic equipment, Regulation 706.411.1.2 requires equipotential bonding to be provided, connecting together all exposed-conductive-parts within the location (such a metallic conduits and equipment enclosures), extraneous-conductive-parts (metallic parts of the location) and the functional earth. Fig 4 shows an example of this arrangement.
Correction to article on pages 44 to 46 of Connections issue 187 (Autumn 2013)
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There is an error in the above article, entitled Cables in spaces containing thermal insulation, in the previous issue of Connections.
the words ‘a tabulated current-carrying capacity’ should be replaced by the words ‘an effective current-carrying capacity’.
On the third line of the last paragraph on page 45,
We apologise for the error.
Winter 2013-14 Connections
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