Wiring Types Codes – What Are They and What Can You Do to Identify Them?
UK cable colours changed some years ago, and the change catches people out to this day. The harmonised colours we use now — brown, blue and green-and-yellow — were introduced by Amendment 2:2004 to BS 7671:2001, published on 31 March 2004. They are not, as is often claimed, a change brought in by the 18th Edition.
The current version of the Wiring Regulations is BS 7671:2018+A4:2026 (Amendment 4, published 15 April 2026). Revisions like this are routine: standards are updated for greater safety and consistency throughout the UK.
This simple guide will cover information on identifying the common wiring and cables you may encounter — and, just as importantly, what to do when you are not sure.
Last reviewed: September 2026.
Wire Colour Coding Explained
It’s important to know the correct colours before working on any electrical system. Earth (protective) conductors are green-and-yellow. Live is brown and neutral is blue.
Properly labelled electrical wiring will make electric power distribution smoother and ensure that every electrical cable in a building functions properly. This holds whether your job site is a home or an office.
These colours won’t tell you the voltage or the size of the conductor, but they do tell you its function.
Check the wiring regulations for more information on current BS 7671 colour codes.
If in doubt, stop and use a qualified electrician. Colour identification is a starting point, never a substitute for safe isolation and proving dead with an approved voltage indicator.
What Classifies as a DIY Project?
Before you begin laying a new cable through your wall, check whether your proposed project requires a professional electrician’s input.
Minor work such as replacing a like-for-like accessory can generally be done by a competent homeowner, but proceed with caution and always isolate first.
Certain work is notifiable. In England and Wales, installing a new circuit, replacing a consumer unit, and (in Wales) work in kitchens and outdoors falls under Part P of the Building Regulations and must be notified to building control or carried out by a registered competent person. In Scotland, electrical work must comply with the Building Standards and a completion certificate may be required. Consumer unit replacement is not DIY work in any part of the UK.
If you’re training to become a professional electrician, prepare properly with an 18th-edition mock exam.
Different Wiring Types – Current Colours
BS 7671:2018+A4:2026 is the current edition of the Wiring Regulations, and new installation work is expected to comply with it.
The colour requirements themselves date from Amendment 2:2004. During the transition period — work commencing on site between 31 March 2004 and 31 March 2006 — installers could use either the old or the harmonised colours, but not both in the same installation. From 1 April 2006, new installation work has had to use the harmonised colours.
This only applies to new wiring and cable work. Wiring installed before that date will commonly still be in the old colours, and there is no requirement to rewire purely because of colour.
NOTE: You may not be able to tell from colour alone whether you’re dealing with a line or neutral conductor — particularly in an older or altered installation. Treat every conductor as live until it has been safely isolated and proved dead.
Earth – Green and Yellow
Earth (protective) conductors are identified by green-and-yellow — not plain green. In BS 7671 terms this is the circuit protective conductor, or CPC.
Two points matter here, and they are the ones most often got wrong:
A CPC normally carries no current at all. It is not a “small voltage” conductor. It sits at or near earth potential in normal service, which is exactly why it is safe to touch a properly earthed appliance case. Under fault conditions, however, it may carry the full prospective earth fault current for the time it takes the protective device to operate. That is what it is sized for.
A bare CPC must be sleeved. In twin-and-earth cable the CPC is supplied bare inside the sheath, and this is normal — but as soon as the sheath is stripped back, that conductor must be covered with green-and-yellow sleeving at every termination: consumer unit, socket and switch back boxes, junction boxes, ceiling roses, everywhere. This is a requirement of BS 7671 (Regulation 514.4.2). An unsleeved bare earth at a terminal is a defect, not a safe or acceptable arrangement, and it is one of the most common faults found on domestic inspections.
The earth conductor’s job is to provide a low-impedance path back to the source of supply so that a fault causes the protective device to disconnect quickly. On the great majority of UK supplies (TN-C-S or TN-S) that path is through the supply cable back to the distribution transformer, not into a plate in the garden. Only TT installations rely on an earth electrode, and those depend on an RCD for disconnection.
Live – Brown
Line (live) conductors are brown, and they are the ones that will give you a shock. Exercise caution when handling this type of wire.
Insulation degrades over time, particularly where cables have been overloaded, run hot, or exposed to UV or vermin.
Assume any exposed conductor is live regardless of colour or type, and treat it accordingly.
Neutral – Blue
The neutral conductor is blue. It is easy to think of neutral as the “safe” one — it isn’t.
Under BS 7671 the neutral is a live conductor. It carries the same load current as the line conductor, and in a faulty or badly wired installation — a borrowed neutral, a broken PEN conductor, a reversed polarity fault — it can sit at a dangerous voltage relative to earth. A neutral is only safe to touch once the circuit has been safely isolated and proved dead.
Never assume a blue conductor is dead because it is blue. Prove it.
Old Colours
Here is how the old and current schemes compare. This is the table to keep to hand when you open up an older installation.
Single-phase
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Download information pack| Function | Old colour (pre-2006) | Current colour |
| Line (live) | Red | Brown |
| Neutral | Black | Blue |
| Earth (CPC) | Green, or green-and-yellow | Green-and-yellow |
Three-phase
| Function | Old colour (pre-2006) | Current colour |
| Line 1 | Red | Brown |
| Line 2 | Yellow | Black |
| Line 3 | Blue | Grey |
| Neutral | Black | Blue |
| Earth (CPC) | Green, or green-and-yellow | Green-and-yellow |
The dangerous overlap is obvious once it’s set out like this: blue was a line colour and is now neutral, and black was neutral and is now a line colour. In a three-phase installation that has been altered over the years, a black or blue conductor could be either. Older installations may also still have plain green earths, which is why green-and-yellow sleeving matters at every termination you touch.
Where old and new colours meet in the same installation, BS 7671 requires a warning notice at the distribution board. If you find one, take it seriously — and if the installation isn’t clearly and consistently identified, get a qualified electrician to test and label it before any further work.
Australian and US Colour Codes
We’ve included this section in case you encounter wiring that doesn’t match the current UK colours.
Australian Wire Colours
Australia and New Zealand moved to the same harmonised scheme under AS/NZS 3000, so current Australian colours match the UK.
Current Colour Scheme (AS/NZS 3000)
- Earth – Green and Yellow
- Active (live) – Brown
- Neutral – Blue
- Three-phase actives – Brown, Black, Grey
Older Colour Scheme
- Earth – Green
- Active (live) – Red
- Neutral – Black
- Three-phase actives – Red, White, Blue
You may still find white used as an active conductor in older Australian installations and in some flexible cords — it is not a current standard active colour, but it is worth recognising.
US Wire Colours
The US works to the National Electrical Code (NEC), and the logic is different from ours. The NEC only mandates the colours of two conductors: the grounded (neutral) conductor must be white or grey, and the equipment grounding conductor must be green, green-with-yellow-stripe, or bare. Phase (ungrounded) conductor colours are convention rather than code, and they are used to distinguish one system voltage from another.
120/208 V systems
- Ground – Green or bare
- Phases – Black, Red, Blue
- Neutral – White
277/480 V systems
- Ground – Green or bare
- Phases – Brown, Orange, Yellow
- Neutral – Grey
Different Types of Wiring
Here we’ll identify some of the different types of cable that you’ll typically find.
- Twin and Earth (6242Y) – The standard cable for UK domestic circuits. Two insulated cores (brown line, blue neutral) plus a bare CPC running between them under the sheath. That bare CPC must be sleeved green-and-yellow wherever it is terminated. Older twin and earth will have red and black cores instead.
- Three-Core and Earth (6243Y) – Three insulated cores (brown, black, grey) plus a bare CPC, used for two-way lighting and similar. In older cable the cores are red, yellow and blue.
- Flexible cord – Used for appliances and light fittings; always has an insulated green-and-yellow earth core where an earth is required.
- SWA (steel wire armoured) – Used for buried and external runs; the armour may serve as the CPC, in which case it must be correctly terminated with a suitable gland and earth tail.
How Else Can You Identify Wiring?
Apart from colour, the most reliable way to identify a cable is through the printing on its sheath. UK cable is marked with the cable type, core size and applicable British Standard.
Carefully inspect the cable for this printing. Colour alone is never enough in an installation that may have been altered.
Mains Fuse Box
After all the electrical wiring in a home has been installed, it’s important to know where the consumer unit is in case you need to isolate the supply.
The consumer unit contains the main switch and the protective devices for each circuit.
- Main Switch – Isolates the whole installation, switching off the supply to every circuit downstream of it. Note that the supply tails between the meter and the main switch remain live.
- RCD (Residual Current Device) – Detects an imbalance between line and neutral current, which indicates current leaking to earth, and disconnects. This is the protection that reduces the risk of a fatal shock.
- MCB (Miniature Circuit Breaker) – Protects the cable against overload and short circuit. An MCB does not protect against earth leakage, which is a different job entirely.
- RCBO – Combines both functions in one device, so a fault on one circuit doesn’t take out the others.
Frequently Asked Questions (FAQs)
Check this section for more information on electrical cable installation.
Is 18th Edition Certification Training Mandatory?
Before you carry out electrical installation work, we recommend undergoing 18th edition training to work to the current BS 7671 standard — now BS 7671:2018+A4:2026. The previous version, BS 7671:2018+A2:2022+A3:2024, is withdrawn on 15 October 2026, so anyone certified against the earlier amendment should plan an update.
The qualification itself isn’t a legal requirement, but it is the recognised evidence that you know the current Regulations, and employers and scheme operators expect it.
To note: holding the 18th Edition qualification does not by itself let you self-certify your work. Self-certification comes from registration with a competent person scheme (such as NICEIC, NAPIT or SELECT), for which the qualification is one of the entry requirements.
BS 7671 sets the standard for a safe installation. Complying with it is the objective; exceeding it where the situation warrants is good practice.
What Is a Conduit?
An electrical conduit is a tube or pipe designed to protect the cables running through it. Conduits are useful when running a cable to an outdoor installation such as a shed.
All conduit has a maximum cable capacity, which depends on the conduit size, the number and size of the cables, and the number of bends in the run. Overfilled conduit makes cables difficult to draw in and can affect their current-carrying capacity.
What’s the Difference Between Cables and Wires?
A wire and a cable may seem the same, but there is a difference. A wire is a single conductor, while a cable is an assembly of conductors within an overall sheath.
Both are typically insulated with PVC, LSZH or rubber compounds.
Conclusion
It’s helpful to revisit the basics before you begin any cable work, whether you’ve turned your home into a DIY project or you’re on the job.
Two things are worth taking away above everything else. Earth is green-and-yellow, never plain green — and a bare CPC must be sleeved green-and-yellow at every termination. And blue and black swapped roles in 2006, so in any altered installation, colour is a clue rather than proof.
If your installation has a number of different cables and circuits, remember to include easy-to-access information on clearly-printed labels for future maintenance work.
And the rule that overrides all of the above: if you are not certain what you are looking at, stop and call in a qualified electrician. Identifying a conductor wrongly is one of the few DIY mistakes that can kill somebody.
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