Last updated: 26th August 2026 | Originally published: 19th May 2025
If you are wondering what colour the live wire is in the UK, the short answer is brown in current single-phase fixed wiring. The neutral wire is blue and the earth wire is green-and-yellow. In older wiring, however, the live wire is usually red and the neutral is black.
In this guide, we’ll break down everything you need to know about live wire colour, the full set of UK wiring colours, how the standards have changed over time, and why it all matters for safety, compliance, and fixed wire testing. Whether you’re a DIY enthusiast, a landlord, or a budding electrician, understanding wire colours is essential to keeping your property safe and up to code.
Electrical safety warning: Do not touch, disconnect or alter electrical wiring unless you are competent to do the work. Colour is only an identification aid. A circuit must be safely isolated and proven dead with suitable test equipment before work starts.
What colour is the live wire in the UK?
In current UK single-phase fixed wiring, the live conductor is brown. It carries electrical energy from the supply to a circuit, accessory or appliance.
In older UK fixed wiring, the live conductor is normally red. The UK moved to harmonised cable colours during a transition that began in 2004, with the current colours becoming mandatory for new fixed-wiring work from 1 April 2006.
Most domestic properties use single-phase electricity, so brown is the live wire colour most people will see in a newer consumer unit, socket circuit or lighting circuit. But the answer changes when you are looking at three-phase wiring, as black and grey can also be live line conductors.
UK wiring colours at a glance
In twin-and-earth cable, the CPC is often bare copper inside the cable sheath. It should be sleeved green-and-yellow where it is terminated so that its function is clear.
What do the live, neutral and earth wires do?
Electrical cable colours make it easier to identify a conductor’s intended function. They are important, but they are not a substitute for correct testing, installation and verification.
- Live or line: carries electrical energy from the supply. It is brown in current single-phase wiring and red in older wiring.
- Neutral: normally completes the circuit back to the supply. It is blue in current wiring and black in older single-phase wiring.
- Earth or circuit protective conductor (CPC): is there for protection. It provides a path for fault current, helping protective devices operate if a fault makes exposed metalwork dangerous.
Neutral is not a safe wire to touch. A neutral conductor can still be live in certain fault conditions, when circuits are incorrectly connected or where there are other sources of energy.
Old UK wiring colours: red, black and green-and-yellow
You may still find the older colour system in homes, workplaces and public buildings. Its presence does not automatically mean that an installation is unsafe or that the property needs a full rewire.
For older single-phase fixed wiring, the normal identification is:
- Red: live or line
- Black: neutral
- Green-and-yellow: earth or CPC
Very old installations may use other materials, cable types or colours. For example, some older earth conductors may be green, and installations may have been extended several times. That is why electricians identify and test conductors rather than relying on a visual check.
When did UK wire colours change?
The UK introduced harmonised fixed-wiring colours in 2004, with a transition period before the current system became mandatory for new fixed-wiring work from 1 April 2006. The change was not retrospective: an existing installation did not need to be rewired solely because it used red and black conductors.
The main concern is clarity when old and new colours are present together. Where work has added current-colour cable to an existing old-colour installation, the installation should be clearly identified with the appropriate warning notice at the consumer unit or distribution board.
Important: A property with red and black wiring has not necessarily been “partially updated”. Mixed colours can result from later additions, alterations or repairs. A competent electrician should establish exactly what is present before any work is carried out.
Three-phase wire colours in the UK
Three-phase electricity is commonly found in commercial premises, workshops, plant rooms and larger buildings. It can also be present in some homes, particularly where there is high electrical demand.
The current three-phase line colours are brown, black and grey. This is where simple rules such as “black means neutral” can become dangerous.
Why black and blue wires need extra care
In a current three-phase installation, black is L2, so it is a live line conductor. In an older three-phase installation, black is normally neutral. The reverse is true for blue: it is neutral in current wiring, but it was L3, a live line conductor, in the older three-phase colour system.
For that reason, do not make assumptions about black or blue conductors in commercial, industrial or mixed-age installations. Correct identification, safe isolation and testing are essential.
Can black or grey wires be live at a light switch?
Yes. Three-core-and-earth cable is often used for two-way switching, which lets one light be controlled from two different locations, such as at the top and bottom of a staircase.
In these circuits, black and grey cores may be used as line conductors or switch wires rather than neutrals. Where a blue, black or grey conductor is used as a line conductor, it should be appropriately identified at its terminations, commonly with brown sleeving or marking.
This is another reason why wire colour by itself cannot tell you whether a cable is live, neutral or safe to work on.
What should you do if you find mixed wiring colours?
Mixed old and new wire colours are common in properties that have been altered over time. They do not automatically mean the installation is dangerous, but they do make good identification and documentation more important.
- Do not guess: never decide a conductor’s function from colour alone.
- Look for warning labels: the consumer unit or distribution board should carry appropriate identification where both colour systems are present.
- Check the condition: signs of damage, ageing accessories, loose connections, overheating or poor previous work should be investigated.
- Use a competent electrician: they can inspect, test and identify the installation properly.
- Consider an EICR: if the condition, age or safety of the fixed installation is uncertain, an Electrical Installation Condition Report can provide a documented assessment.
Do old wiring colours mean a property needs rewiring?
No. Red and black conductors alone are not a reason to rewire a property. Existing installations were not required to be changed merely because the harmonised colours were introduced.
Whether a rewire is needed depends on the overall condition and suitability of the installation. An electrician may recommend further work if there is deteriorated cable insulation, damaged accessories, inadequate protective measures, unsafe alterations, insufficient capacity for current use or faults identified during inspection and testing.
If you are buying a property, managing a rental home, planning major alterations or simply do not know the condition of the wiring, it is sensible to discuss an EICR with a competent electrician.
Why wire colours matter for electrical safety
Correct colour identification helps electricians work safely and efficiently. It also supports inspection, testing, maintenance and fault-finding. But the most important point is that colours are only one part of safe electrical work.
The legal framework sits in the Electricity at Work Regulations 1989. Regulation 4 requires electrical systems to be constructed and maintained so as to prevent danger, and regulation 14 sets out the strict conditions under which work on or near live conductors may be carried out. Regulation 16 requires that people are competent for the work they undertake.
In practice that means the correct circuit must be isolated securely and proven dead using suitable equipment before anyone works on conductors. Switching a circuit off is not enough on its own. HSE guidance note GS38 sets out what suitable test equipment looks like, including the use of an approved voltage indicator and the prove, test, prove sequence.
For businesses and duty holders, fixed electrical installations should also be maintained so that danger is prevented. The appropriate inspection and testing programme depends on the type of installation, how it is used, its environment and the level of risk.
Learn more about electrical training
Understanding cable colours is a useful starting point, but working safely on electrical installations requires practical competence, sound technical knowledge and an understanding of the current requirements.
Logic4training offers electrical training courses for people starting out in the trade and experienced electricians looking to update their skills. You can also explore our 18th Edition training and electrical inspection and testing options.
FAQs
What colour is the live wire in the UK?
In current UK single-phase fixed wiring, the live or line conductor is brown. In older fixed wiring, it is usually red.
What colour is the neutral wire in the UK?
In current UK fixed wiring, neutral is blue. In older single-phase wiring, neutral is usually black. Remember that blue was used as L3 in older three-phase systems, so it should not be assumed to be neutral in every installation.
What colour is the earth wire in the UK?
The earth or circuit protective conductor is green-and-yellow. In very old installations, you may find a green earth conductor. In twin-and-earth cable, the CPC may be bare copper and should be sleeved green-and-yellow at its terminations.
Is a black wire live or neutral in the UK?
It depends on the system. Black is normally neutral in older single-phase wiring, but it is L2, a live line conductor, in current three-phase wiring. It can also be used as a line conductor in some switching arrangements when correctly identified.
Is a blue wire live or neutral in the UK?
Blue is neutral in current UK fixed wiring. In older three-phase wiring, however, blue is L3, which is a live line conductor. Always have conductors correctly identified and tested before work.
What are the old UK wiring colours?
For older single-phase fixed wiring, red is live, black is neutral and green-and-yellow is earth. Some very old installations may vary, so colour should not be used as the only means of identification.
What are the current UK three-phase wire colours?
The current three-phase colours are brown for L1, black for L2, grey for L3, blue for neutral and green-and-yellow for earth. The older system used red, yellow and blue for the three line conductors, with black neutral.
When did UK wiring colours change?
Harmonised colours were introduced for UK fixed wiring in 2004. After a transition period, they became mandatory for new fixed-wiring work from 1 April 2006.
Does old wiring need to be replaced?
Not necessarily. Old cable colours alone do not mean a rewire is required. A competent electrician should assess the installation’s condition, safety and suitability if there are concerns.
Can I identify a wire just by its colour?
No. Colour is an identification aid only. Previous alterations, incorrect work, fading and mixed old/new wiring can all make visual assumptions unsafe. The circuit must be safely isolated and conductors proven dead before electrical work begins.
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