Cable Colour Codes UK
Complete Reference for Electricians

Every UK conductor colour in one table. The current colours come from Table 51 of BS 7671, introduced by Amendment 2 to BS 7671:2001 (issued March 2004) and mandatory for new installations from 31 March 2006. The old colours were compliant when installed and are still found throughout the existing housing stock.

Why the colours are called “harmonised”

The colours align with the code used across Europe under the CENELEC harmonisation documents. Before harmonisation each country ran its own scheme, which created real confusion around imported equipment and for anyone working across borders. The UK adopted the harmonised set at Amendment 2 to BS 7671:2001 with a transitional period ending in 2006.

Which cables the colours apply to

Table 51 identification applies to all fixed wiring — twin and earth (flat cable), SWA (steel wire armoured), MICC (mineral insulated), and singles in conduit or trunking. The protective conductor in twin and earth cable is a bare copper conductor and carries no insulation colour of its own, so it is identified with green-and-yellow sleeving at its terminations.

The old UK colour code ran for decades before harmonisation. Any property not rewired since before 2006 is likely to be on it, so every electrician must be able to read it during inspection and testing. The colours themselves are in the chart above; what matters on site is where the two schemes collide.

Old-colour wiring does not have to be replaced. What does have to be right is the identification: switch wires sleeved, bare protective conductors sleeved at terminations, and — as good practice rather than regulation — a caution notice at the board where both schemes are present.

The three-phase change was the more significant half of harmonisation. It introduced two colours that had not been line colours before (black and grey) and moved blue from a line colour to the neutral. The full mapping is in the chart above; the practical consequences are below.

This matters most for distribution board wiring and three-phase installations, where several colour schemes can meet inside one enclosure.

Flexible cables take their identification from the same Table 51 as fixed wiring: brown line, blue neutral, green-and-yellow protective conductor. Flex was already on these colours before fixed wiring changed in 2004, so the harmonisation did not alter flex — one reason red-and-black flex does not appear on modern appliances.

Current-carrying capacity is a separate question from colour. It depends on conductor cross-sectional area, installation method and ambient temperature — take it from the manufacturer’s data and BS 7671 Appendix 4 for the specific flex type and condition, never from the colour or a rule of thumb.

Section 514 of BS 7671 sets out conductor identification. Regulation 514.3.1 requires that, except where identification is not required by Regulation 514.6, cores of cables shall be identified by colour as required by Regulation 514.4 and/or by letters and numbers as required by Regulation 514.5. Regulation 514.3.2 adds that every core shall be identifiable at its terminations and preferably throughout its length, and that binding and sleeves used for identification shall comply with BS 3858 where appropriate.

Identification of conductors (514.3.1) is a listed item on the schedule of inspections. During an EICR, missing or incorrect identification is recorded as an observation: missing protective conductor sleeving is typically coded C3, while a missing switch-wire identification that creates a polarity risk may be coded C2. Coding remains the inspector’s judgement — BS 7671 does not prescribe a code for either.

Many UK installations contain wiring from both colour codes. That is entirely lawful — the old colours were compliant when installed and do not need replacing. What it creates is an identification risk that has to be managed, and the regulatory position has changed.

The On-Site Guide (Reg 6.12, “Warning notice — non-standard colours”) continues to recommend a caution notice at or near the appropriate distribution board where additions or alterations have left some wiring in the harmonised colours and some in the earlier colours. Figure 6.12 of the Guide shows the wording:

“Caution — This installation has wiring colours to two versions of BS 7671. Great care should be taken before undertaking extension, alteration or repair that all conductors are correctly identified.”

On-Site Guide, Reg 6.12 / Figure 6.12 — recommendation, not a BS 7671 requirement

The notice should be durable and legible, and positioned at or near the consumer unit or distribution board where circuits of both codes are present. Self-adhesive labels are available from wholesalers, or the notice can be printed and laminated.

During an EICR inspection, check every board in a mixed-colour installation. Fitting the notice remains good practice, but if it is absent there is no operative BS 7671 clause to cite against it and the standard prescribes no C-code.

In the app

UK Wiring Colour Codes: Old vs New (BS 7671)

UK cable colour codes explained: the new harmonised colours vs the old red and black, for single, twin & earth and three-phase, with a comparison.

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Two notice requirements in Section 514 come up constantly on modern boards and are worth separating from the deleted 514.14. Neither is new at A4:2026 — Regulation 514.15 is carried from BS 7671:2018 and Regulation 514.16.1 was introduced at A2:2022 — but both are live and both are commonly missed.

On an EICR covering an installation with solar PV, battery storage or SPDs, check for these notices and record their absence as an observation where the requirement applies.

Sleeving is how you satisfy Regulation 514.3.2 — every core identifiable at its terminations — when the factory insulation colour does not match the conductor’s function. Binding and identification sleeves are to comply with BS 3858 where appropriate. Two applications account for almost all of it.

Sleeving must be the correct colour, the correct size for the conductor, and fitted so it cannot slide or fall off. Heat-shrink gives a more secure fit than push-on PVC.

Identification errors are among the most common EICR findings. These four account for most of them.

In the app

20 Pair Colour Code UK Cable Guide

20 pair cable colour codes explained for UK electricians. BS 7671:2018+A4:2026 compliant identification. Quick reference chart and installation rules.

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