UK Cable Colour Codes
Current harmonised colours, old UK colours, DC, SWA, and flex
BS 7671 Table 51, Regulation 514.14.1
When Did Colours Change?
The UK adopted harmonised European cable colours on 1 April 2004 (Amendment 2 of BS 7671:2001), aligning fixed wiring with the Brown/Blue/Green-Yellow flex colours already standard since 1969. The transition period ended 1 April 2006 — all new work after that date must use harmonised colours.
Current Colours — Fixed Wiring (Post-2004)
BS 7671 Table 51 — IEC 60446 / CENELEC HD 384.5.514
| Function | Single Phase | 3Ø L1 | 3Ø L2 | 3Ø L3 |
|---|---|---|---|---|
| Line (L) | Brown | Brown | Black | Grey |
| Neutral (N) | Blue | Blue | Blue | Blue |
| Earth (E / CPC) | Green/Yellow | Green/Yellow | Green/Yellow | Green/Yellow |
Old Colours — Fixed Wiring (Pre-2004)
Still found in pre-2004 installations. Pre-1977 may have solid green earth or bare copper CPC.
| Function | Single Phase | 3Ø L1 | 3Ø L2 | 3Ø L3 |
|---|---|---|---|---|
| Line (L) | Red | Red | Yellow | Blue |
| Neutral (N) | Black | Black | Black | Black |
| Earth (E / CPC) | Green/Yellow | Green/Yellow | Green/Yellow | Green/Yellow |
Flexible Cable (Flex) Colours
Brown/Blue/Green-Yellow has been standard for flex cords since 1969. Older appliances may have Red (Line), Black (Neutral), Green (Earth).
DC Conductor Colours (BS 7671 Table 51)
Relevant for solar PV, battery storage, and EV DC charging
| DC System | Positive (L+) | Negative (L-) | Mid-wire (M) |
|---|---|---|---|
| Unearthed 2-wire | Brown | Grey | — |
| Earthed 2-wire (neg. earthed) | Brown | Blue | — |
| 3-wire | Brown | Grey | Blue |
SWA Cable Core Colours (BS 5467)
| Cable Type | Core Colours |
|---|---|
| 2-core | Brown, Blue |
| 3-core | Brown, Black, Grey |
| 4-core | Brown, Black, Grey, Blue |
| 5-core | Brown, Black, Grey, Blue, Green/Yellow |
When 3-core SWA is used for single-phase, the unused cores repurposed as neutral or earth must be sleeved with the appropriate colour (blue for N, green/yellow for E) at every termination. Cables with 7+ cores use white cores with black printed numbers (“0” = neutral).
Where old and new colours overlap — black and blue have swapped roles and are the most dangerous confusion points
| Conductor | Old Meaning | New Meaning | Risk |
|---|---|---|---|
| Black conductor | Neutral (single-phase) | Line L2 (three-phase) | Treating a live conductor as neutral |
| Blue conductor | Line L3 (three-phase) | Neutral | Treating a live conductor as neutral |
| Red conductor | Line (single/three-phase L1) | Not used | Indicates old installation — test before working |
| Yellow conductor | Line L2 (three-phase) | Not used (except earth stripe) | Indicates old installation — test before working |
Regulation 514.14.1 — Required Caution Notice
When an installation contains both old and harmonised colours, this notice must be permanently fixed at or near the distribution board:
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.
Absence of this notice in a mixed installation is coded C3 (Improvement Recommended) on an EICR.
Lighting Circuit Sleeving
- • Switched live: When a blue core is used as a line conductor in a switch drop, it must be sleeved with brown at both the switch and ceiling rose.
- • Two-way strappers: In 3-core & earth cable (Brown, Black, Grey), the Black and Grey cores acting as switch wires must be sleeved with brown at all terminations.
- • Bare CPC: Must always be sleeved green/yellow at every termination point.
Harmonisation Timeline
| Date | Status | Colours |
|---|---|---|
| Pre-March 2004 | 16th Edition | Legacy: Red (Live), Black (Neutral) |
| 31 March 2004 | Amendment 2 published | Harmonised colours introduced |
| April 2004 – March 2006 | Transition period | Either system permitted |
| 1 April 2006 | Mandatory compliance | Harmonised colours required for all new work |
Current (Post-2004)
Brown = Line (Live)
Blue = Neutral
Green/Yellow = Earth
Old (Pre-2004)
Red = Line (Live)
Black = Neutral
Green/Yellow = Earth