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58 Minimising danger from the mis-identification of conductors 60 Periodic inspection and testing of electrical installations that include a micro-generator 65 Premature collapse of wiring systems 68 Variable frequency drives 72 The installation of extra-low voltage tungsten halogen lighting 76 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 diff erent colours of insulation for line and neutral conductors, and that the colour of insulation will not necessarily describe its function.

In 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 PreAmd 2 colours PostAmd 2 colours

Line of a single-phase a.c. circuit Red Brown

Neutral of a single or three-phase a.c. circuit Line 1 of a three-phase a.c. circuit Black Blue

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, Regulation 514.3.2 permits conductors to be identifi ed at the terminations rather than throughout their length – although identifi cation 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 identifi ed in some other acceptable fashion to identify the function of the conductor.

It is important, therefore, that the function of a conductor is properly identifi ed 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 identifi ed by both old (pre-Amd 2) and new colours (post-Amd 2), and therefore, it should never be presumed that a conductor identifi ed by a specifi c colour functions as expected. Indeed, it might be the case that there has been mis-identifi cation of conductor function in the original installation.

In accordance with Chapter 61 (initial verifi cation) 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 identifi ed by old colours

It is imperative that every installation is inspected and tested (including identifi cation 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 diff erent ‘function’ permutations for conductors, and hence emphasises the potential danger in a single-phase fi nal circuit containing lighting and extractor fans wired in 70° C thermoplastic fl at cable (3-core and 4-core) where conductors are identifi ed by

Fig 1 Example of identification of conductors

Table 2: Example of the possibility of conductor identifi cation

Conductor function Colour identification of insulation Cable Old colours New colours type

Permanent line Red Permanent line Red Permanent line Red Brown Brown Brown 2-core 3-core 4-core

Permanent line Yellow Permanent line Blue Grey Black

4-core 4-core Permanent line Black Blue 4-core Switch line Black (sleeved red) Blue (sleeved brown) 2-core Switch line Yellow Black 3-core (sleeved red) (sleeved brown) Switch line Blue (sleeved red) Grey 3-core (sleeved brown)

Neutral Black Blue 2-core

Neutral Blue (sleeved black) Grey/Black/Brown (sleeved blue) 4-core insulation having both old and new colours.

Presumed or incorrect identifi cation of conductors may result in a range of outcomes and potential dangers, either at the point of connection or further downstream.

In the light of the potential outcomes caused by ‘colour confusion’, where an existing installation (wired in conductors having old colours) is added to and/or altered using conductors identifi ed by new colours, a warning notice is required to be fi xed at or near the appropriate distribution board, to provide a warning to persons working on the installation in the future (Regulation 514.14.1 and Fig 1 refer).

Indeed, such a notice should also act as to warn contractors to correctly ascertain the function of individual conductors before work is carried out on an existing installation.

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