Ask the experts/Technical
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Minimising danger from the mis-identification of conductors Periodic inspection and testing of electrical installations that include a micro-generator Premature collapse of wiring systems
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Variable frequency drives The installation of extra-low voltage tungsten halogen lighting Snags & Solutions: now updated to Amendment No 3 of BS 7671 and, where appropriate, BS 5266 and BS 5839
Minimising danger from the mis-identification of conductors Objective To remind contractors that many installations will have different colours of insulation for line and neutral conductors, and that the colour of insulation will not necessarily describe its function.
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n 2004, Amendment 2 of BS 7671: 2001 introduced changes to the colours used to identify the cores of a cable (typically by insulation). This change to insulation colours was widely reported by the industry, and while it is permissible to use some form of alphanumeric notation to identify conductors, most installations will contain a mixture of conductor insulation colours. Table 1: Insulation colours pre- and post -Amd 2 BS 7671: 2004 Conductor
PrePostAmd 2 Amd 2 colours colours
Line of a single-phase a.c. circuit
Red
Brown
Neutral of a single or three-phase a.c. circuit
Black
Blue
Line 1 of a three-phase a.c. circuit
Red
Brown
Line 2 of a three-phase a.c. circuit
Yellow
Black
Line 3 of a three-phase a.c. circuit
Blue
Grey
The change in colours used to identify a conductor’s function may lead to confusion, for example, where the blue insulated line conductor of a three-phase supply is mistaken for the neutral conductor. Furthermore, 58
Regulation 514.3.2 permits conductors to be identified at the terminations rather than throughout their length – although identification throughout its length is preferred. For example, it is permissible to use the blue insulated conductor (neutral conductor) as a line conductor where, for example, no neutral is required at a load. Such a conductor would have to be oversleeved or identified in some other acceptable fashion to identify the function of the conductor. It is important, therefore, that the function of a conductor is properly identified prior to any work being carried out on an installation (refer Fig 1). Verifying the function of a conductor The previous example highlights the dangers for contractors who are planning to work on, or connect to, existing installations containing conductors identified by both old (pre-Amd 2) and new colours (post-Amd 2), and therefore, it should never be presumed that a conductor identified by a specific colour functions as expected. Indeed, it might be the case that there has been mis-identification of conductor function in the original installation. In accordance with Chapter 61 (initial verification) of BS 7671, appropriate inspection and testing should always be carried out to verify, among other things, the function of a conductor in relation to the colour of its insulation. Making additions, alterations or repairs to an existing installation containing conductors identified by old colours It is imperative that every installation is inspected and tested (including identification of conductors) during erection and on completion before being put into service, to minimise the risk of injury to persons and/or damage to equipment or property (Regulation 610.1 refers). Table 2 highlights the different ‘function’ permutations for conductors, and hence emphasises the potential danger in a single-phase final circuit containing lighting and extractor fans wired in 70° C thermoplastic flat cable (3-core and 4-core) where conductors are identified by
Summer 2016 Connections
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