Old vs New Cable Colours: Wiring Colour Code Reference Guide
Quick Answer: The UK harmonised cable colours on 31 March 2004 (mandatory from 1 April 2006). Single phase changed from red (live) / black (neutral) to brown (live) / blue (neutral). Three phase changed from red/yellow/blue to brown/black/grey. Earth (CPC) remained green/yellow throughout.
Summary
The UK adopted harmonised European cable colours under Amendment No. 2 to BS 7671:2001 (the 16th Edition), published in 2004 and enforceable from 1 April 2006. The change aligned the UK with IEC 60446 and CENELEC HD 308 S2 standards used across Europe. During the two-year transition period (April 2004 to March 2006), either old or new colours could be used in a single installation, but mixing was not permitted. The most dangerous overlap is that the old neutral colour (black) is now a live phase colour (L2) in three-phase systems, and the old three-phase L3 colour (blue) is now the single-phase neutral. Any installation containing both old and new colours requires a caution notice under Regulation 514.14.1 of BS 7671.
Key Facts
- The colour change became mandatory on 1 April 2006 for all new installations and alterations in the UK
- During the transition (1 April 2004 to 31 March 2006), either old or new colours were permitted but not mixed within a single installation
- Flexible cable (flex) for appliances has used brown/blue/green-yellow since the 1970s -- it was not affected by the 2006 change
- The earth conductor (CPC) colour is unchanged: green/yellow striped (or bare copper sleeved green/yellow)
- The change was driven by European harmonisation -- the old UK red/black system was unique and caused confusion on cross-border projects
- Black is the most dangerous colour to encounter -- it was neutral in the old single-phase system but is now L2 (live) in the new three-phase system
- Blue is equally hazardous in reverse -- it was L3 (live) in old three-phase but is now neutral in the new system
- Installations with mixed colours must display a warning notice at every distribution board (Regulation 514.14.1)
Single Phase Colour Comparison
| Function | Old Colour (pre-2006) | New Colour (post-2006) |
|---|---|---|
| Line (Live) | Red | Brown |
| Neutral | Black | Blue |
| Earth (CPC) | Green/Yellow | Green/Yellow (unchanged) |
Note: Pre-1976 installations may have a solid green earth (no yellow stripe) or a bare uninsulated conductor. Very old installations (pre-1960s) may use tough rubber sheathed (TRS) or lead-sheathed cable with different colour conventions entirely.
Three Phase Colour Comparison
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Try squote free →| Function | Old Colour | New Colour |
|---|---|---|
| L1 | Red | Brown |
| L2 | Yellow | Black |
| L3 | Blue | Grey |
| Neutral | Black | Blue |
| Earth | Green/Yellow | Green/Yellow |
Critical hazard: Old neutral (black) = new L2 (live). Old L3 (blue) = new neutral. Always test with a proven voltage indicator before touching any conductor in a three-phase installation.
Flexible Cable (Flex) Colours
| Function | Colour | Notes |
|---|---|---|
| Live | Brown | Same as new fixed wiring. Flex has used brown since the 1970s |
| Neutral | Blue | Same as new fixed wiring. Flex has used blue since the 1970s |
| Earth | Green/Yellow | Three-core flex only (Class I appliances) |
Flexible cables were harmonised to brown/blue/green-yellow well before fixed wiring followed in 2006. Two-core flex (Class II / double-insulated appliances) has no earth core. The relevant standard for flex is BS 6500 (now superseded by BS EN 50525).
Detailed Guidance
How do I identify old wiring?
Look for the following indicators that an installation uses pre-2006 colours:
- Red and black twin-and-earth cable -- the most obvious sign. The outer sheath is usually grey or white PVC
- Red/yellow/blue three-core-and-earth -- used in three-phase supplies and two-way lighting circuits under the old system
- Bare earth conductors without green/yellow sleeving -- common in older installations where sleeving was applied only at terminations (or sometimes omitted entirely)
- Rubber-sheathed (TRS) cable -- black outer sheath, rubber insulation. Found in pre-1960s installations. If you encounter TRS cable, the installation likely needs a full rewire as the rubber insulation degrades over time
- Lead-sheathed cable -- found in pre-1950s properties. Rubber insulated with a lead outer sheath. Treat as end-of-life
- Imperial-sized cable -- older installations may use imperial gauge cable (e.g. 1/044, 3/029, 7/029) rather than metric mm² sizes
If a property was last rewired before 2006, assume all fixed wiring uses old colours unless evidence suggests otherwise.
How do I handle a mixed installation (old and new colours)?
BS 7671 requires the following when an installation contains wiring to both old and new colour standards:
- Affix a caution notice at or near the consumer unit and at every distribution board in the installation (Regulation 514.14.1)
- Label every conductor at terminations where ambiguity could arise -- use coloured sleeving or adhesive markers to clarify function
- Do not mix old and new colours within the same circuit -- if extending a circuit wired in old colours, either rewire the entire circuit in new colours or continue using old colours for that circuit and apply the caution notice
- Record the situation on the Electrical Installation Certificate or Minor Works Certificate, noting which circuits use which colour system
- Test every conductor with a voltage indicator before making connections -- never assume function from colour alone in a mixed installation
What warning notice do I need at the consumer unit?
Regulation 514.14.1 of BS 7671 requires the following notice to be affixed at or near the consumer unit / 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.
Requirements for the notice:
- Must be placed at or near every distribution board in the installation, not just the main consumer unit
- Must be durable and legible for the expected life of the installation
- Adhesive labels, engraved plates, or printed notices are all acceptable provided they remain legible
- The notice is required even if only one circuit uses old colours and the rest have been rewired in new colours
What about switch wires and two-way switching?
Switch wires are the single biggest source of colour confusion in domestic installations because the cable colours do not directly indicate live/neutral function.
Old system (pre-2006) -- two-way switching with 3-core-and-earth:
- Cores are red, yellow, and blue (plus bare earth)
- All three cores carry switched live -- none is neutral
- Yellow and blue should be sleeved with red tape/sleeving at terminations to indicate they are live, though this was often omitted in practice
New system (post-2006) -- two-way switching with 3-core-and-earth:
- Cores are brown, black, and grey (plus bare earth)
- Brown is typically the permanent live feed; black and grey are strappers (travellers)
- Black and grey cores must be sleeved with brown sleeving at each termination to indicate they are being used as live conductors (Regulation 514.4.1)
Common confusion points:
- In the new system, a blue core used as a switch wire in twin-and-earth cable must be sleeved brown at both ends -- it is carrying switched live, not neutral
- In old two-way circuits, a black core in twin-and-earth used as a switch return should have been sleeved red, but frequently was not
- In intermediate switching (3+ switch locations), identification becomes even more critical -- always trace cables and test before disconnecting
Frequently Asked Questions
Can I extend an old-colour circuit using new-colour cable?
No. BS 7671 does not permit mixing old and new colours within the same circuit. You have two options: rewire the entire circuit in new colours, or continue the extension in old-colour cable (which is still available from specialist suppliers). In either case, a caution notice is required at the distribution board if the overall installation contains both colour systems.
Do I need to rewire an entire property just because it has old colours?
No. There is no legal requirement to rewire simply because old colours are present. Old-colour wiring that is in good condition and passes inspection and testing is perfectly compliant. The requirement is only that any new work from 1 April 2006 onward uses the new harmonised colours, and that a caution notice is fitted if both systems exist in the same installation.
What if I find very old wiring -- solid green earth or no earth at all?
Solid green earth conductors (without the yellow stripe) date from before 1976. Installations from this era may also lack an earth conductor entirely (particularly lighting circuits) or use TRS/lead-sheathed cable. These installations almost certainly require upgrading. The condition of the insulation should be assessed -- rubber insulation from this period is likely degraded and brittle. An Electrical Installation Condition Report (EICR) should be carried out before any work proceeds.
How do I identify conductors in SWA (Steel Wire Armoured) cable?
Multi-core SWA cable follows the same harmonised colour scheme. For example, a 4-core SWA cable uses brown (L1), black (L2), grey (L3), and blue (N). A 3-core SWA has brown, black, and grey cores. Old SWA cable uses the pre-2006 colours (red, yellow, blue, black). The steel wire armouring itself can serve as the circuit protective conductor (CPC) if correctly terminated with brass glands.
Regulations & Standards
BS 7671:2018+A2:2022 (18th Edition, Amendment 2) -- current UK wiring regulations. Regulation 514.14.1 covers the mixed-colour warning notice. Table 51 specifies conductor colour identification
IEC 60445:2021 (formerly IEC 60446) -- international standard for conductor identification by colours or alphanumerics. IEC 60446 was merged into IEC 60445 from the 5th edition (2010) onward
BS EN 60445 -- the UK adoption of IEC 60445
CENELEC HD 308 S2 -- the European harmonisation document that drove the UK colour change
BS 6500 (superseded by BS EN 50525) -- flexible cable standard; flex has used brown/blue/green-yellow since the 1970s
IET -- Harmonised Colours and Alphanumeric Marking (Wiring Matters, Spring 2004)
IET -- The History of Colour Identification of Conductors (Wiring Matters, March 2021)
IET -- Section 514 Identification and Notices (Wiring Matters, November 2020)
RS Components -- A Guide to Electrical Wiring Colours in the UK
Phase 3 Connectors -- Wiring Colours and Electrical Cable Colour Coding Standards
cable sizing -- Cable sizing guide
consumer units -- Consumer unit standards
rcd tripping -- RCD fault diagnosis