Harmonised Cable Core Colours
1 Introduction
The requirements of BS 7671 were harmonized with the technical intent of CENELEC Standard HD 384.5.514: Identification, including 514.3: Identification of conductors, now withdrawn.
Amendment No 2: 2004 (AMD 14905) to BS 7671:2001 implemented the following:
The harmonized cable core colours and the alphanumeric marking of the following standards:
HD 308 S2:2001 Identification of cores in cables and flexible cords
BS EN 60445:2000 Basic and safety principles for man-machine interface, marking and identification of equipment terminals and of terminations
BS EN 60446:2000 Basic and safety principles for man-machine interface, marking and identification. Identification of conductors by colours or numerals.
This appendix provides guidance on marking at the interface between old and harmonized colours and marking general guidance on the colours to be used for conductors.
In the British Standards for fixed and flexible cables, the colours have been harmonized. BS 7671 has been modified to align with these cables but also allows other suitable methods of marking connections by colour (tapes, sleeves or discs), or by alphanumerics (letters and/or numbers). Methods may be mixed within an installation.
2 Addition or alteration to an existing installation
2.1 Single-phase installation
An addition or an alteration made to a single-phase installation need not be marked at the interface provided that:
i) the old cables are correctly identified by the colour red for line and black for neutral, and
ii) the new cables are correctly identified by the colour brown for line and blue for neutral.
2.2 Two- or three-phase installation
Where an addition or alteration is made to a two- or three-phase installation wired in the old core colours with the cable to the new core colours, unambiguous identification is required at the interface. Cores should be marked as follows:
Neutral conductors
Old and new conductors: N
Line conductors
Old and new conductors: L1, L2, L3.
Table 7A – Example of conductor marking at the interface for additions and alterations to an a.c. installation identified with the old cable colours
| Function | Old conductor | New conductor | ||
| Colour | Marking | Marking | Colour | |
| Line 1 of a.c. | Red | L1 | L1 | Brown(1) |
| Line 2 of a.c. | Yellow | L2 | L2 | Black(1) |
| Line 3 of a.c. | Blue | L3 | L3 | Grey(1) |
| Neutral of a.c. | Black | N | N | Blue |
| Protective conductor | Green-and-yellow | Green-and-yellow | ||
3 Switch wires in a new installation or an addition or alteration to an existing installation
Where a two-core cable with cores coloured brown and blue is used as switch wires, both conductors being line conductors, the blue conductor should be marked brown or L at its terminations.
4 Intermediate and two-way switch wires in a new installation or an addition or alteration to an existing installation
Where a three-core cable with cores coloured brown, black and grey is used as switch wires, all three conductors being line conductors, the black and grey conductors should be marked brown or L at their terminations.
5 Line conductors in a new installation or an addition or alteration to an
existing installation
Power circuit line conductors should be coloured as in Table 51. Other line conductors may be brown, black, red, orange, yellow, violet, grey, white, pink or turquoise.
In a two- or three-phase power circuit the line conductors may all be of one of the permitted colours, either identified L1, L2, L3 or marked brown, black, grey at their terminations to show the phases.
6 Changes to cable core colour identification
Table 7B – Cable to BS 6004 (flat cable with bare cpc)
| Cable type | Old core colours | New core colours |
| Single-core + bare cpc | Red or black | Brown or blue |
| Two-core + bare cpc | Red, black | Brown, blue |
| Alt. Two-core + bare cpc | Red, red | Brown, brown |
| Three-core + bare cpc | Red, yellow, blue | Brown, black, grey |
Table 7C – Standard 600/1000V armoured cable
BS 6346, BS 5467 or BS 6724
| Cable type | Old core colours | New core colours |
| Single-core | Red or black | Brown or blue |
| Two-core | Red, black | Brown, blue |
| Three-core | Red, yellow, blue | Brown, black, grey |
| Four-core | Red, yellow, blue, black | Brown, black, grey, blue |
| Five-core | Red, yellow, blue, black,green-and-yellow | Brown, black, grey, blue,green-and-yellow |
Table 7D – Flexible cable to BS 6500
| Cable type | Old core colours | New core colours |
| Two-core | Brown, blue | No change |
| Three-core | Brown, blue, green-and-yellow | No change |
| Four-core | Black, blue, brown,green-and-yellow | Brown, black, grey,green-and-yellow |
| Five-core | Black, blue, brown, black,green-and-yellow | Brown, black, grey, blue,green-and-yellow |
7 Addition or alteration to a d.c. installation
Where an addition or alteration is made to a d.c. installation wired in the old core colours with the cable to the new core colours, unambiguous identification is required at the interface. Cores should be marked as follows:
| Neutral and midpoint conductors | |
| Old and new conductors: | M |
| Line conductors | |
| Old and new conductors: | Brown or grey, or |
| Old and new conductors: | L, L+ or L- |
Table 7E – Example of conductor marking at the interface for additions and alterations to a d.c. installation identified with the old cable colours
| Function | Old conductor | New conductor | ||
| Colour | Marking | Marking | Colour | |
Two-wire unearthed d.c. power circuit |
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| Positive of two-wire circuit | Red | L+ | L+ | Brown |
| Negative of two-wire circuit | Black | L- | L- | Grey |
Two-wire earthed d.c. power circuit |
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| Positive (of negative earthed) circuit | Red | L+ | L+ | Brown |
| Negative (of negative earthed) circuit | Black | M | M | Blue |
| Positive (of positive earthed) circuit | Black | M | M | Blue |
| Negative (of positive earthed) circuit | Blue | L- | L- | Grey |
Three-wired d.c. power circuit |
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| Outer positive of two-wire circuit derived from three-wire system | Red | L+ | L+ | Brown |
| Outer negative of two-wire circuit derived from three-wire system | Red | L- | L- | Grey |
| Positive of three-wire circuit | Red | L+ | L+ | Brown |
| Mid-wire of three-wire circuit | Black | M | M | Blue |
| Negative of three-wire circuit | Blue | L- | L- | Grey |