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UK House Wiring Basics: Colours, Circuits and Safety Explained
Updated October 2026 · Meteor Electrical guides · 10 min read
Quick answer: UK house wiring uses brown for live, blue for neutral and green/yellow for earth. Homes wired before the 2004 to 2006 change may have red (live) and black (neutral). Circuits run from a consumer unit as ring finals for sockets and radials for lighting and big appliances, each protected by an MCB or RCBO, with 30 mA RCD protection on most circuits.
Knowing the basics of UK house wiring helps you spot problems early, buy the right parts and talk clearly with your electrician. This guide covers wiring colours old and new, the main circuit types, what is inside your consumer unit, earthing and bonding, typical cable sizes, and which jobs need a registered electrician.
In this guide
What are the UK house wiring colours?
Modern UK electrical wiring colours follow the harmonised European scheme: brown for live, blue for neutral and green/yellow for earth. The same colours have been used in appliance flex for decades, so fixed wiring and flex now match.
The new colours could be used from 31 March 2004 and became compulsory for all new work from 31 March 2006. Many homes still contain the old red and black cables, and some contain both.
| Conductor | Current colour (from 2004/2006) | Old colour (before 2004) |
|---|---|---|
| Live (line), single-phase | Brown | Red |
| Neutral | Blue | Black |
| Earth (protective conductor) | Green/yellow | Green/yellow (very old installations: green, or bare copper in twin and earth) |
| Line 1, three-phase | Brown | Red |
| Line 2, three-phase | Black | Yellow |
| Line 3, three-phase | Grey | Blue |
Why does the old black wire cause confusion?
In old single-phase wiring, black was neutral. In modern three-phase wiring, black is a line conductor. Also, in a lighting switch drop the blue or black core is often used as a switched live and should be sleeved or marked brown. This is why you can never identify a conductor by colour alone.
Can old and new colours be mixed?
Yes, provided the old wiring is in safe condition. Where an installation contains both colour schemes, BS 7671 requires a warning notice at the consumer unit or distribution board, so anyone working on it knows to check each conductor carefully.
Pro tip: Red and black cables do not automatically mean a rewire is due. What matters is the condition of the insulation and the test results. Rubber-insulated cable, lead sheathing or cloth-covered flex are signs that an inspection is overdue.
What circuits are in a UK house?
A typical UK home has three kinds of final circuit: ring final circuits for sockets, radial circuits for some sockets and fixed appliances, and lighting circuits. Each starts at its own way in the consumer unit and has its own protective device.
Ring final circuits
A ring final circuit, often called a ring main, leaves the consumer unit, loops through each socket and returns to the same terminals. Current reaches every socket by two paths, so 2.5 mm² cable can be protected by a 32 A device. A ring is commonly used for a floor area of up to about 100 m².
Good connections matter. If the ring is broken or a joint is loose, one leg can carry the whole load and overheat, which is why an electrician tests ring continuity end to end.
Radial circuits
A radial circuit runs out from the consumer unit and stops at the last point. Socket radials are common in extensions, garages and kitchens, typically 2.5 mm² on 20 A or 4.0 mm² on 32 A. Radials also feed cookers, showers, immersion heaters and outdoor supplies.
Lighting circuits
Lighting circuits are radials, usually in 1.0 mm² or 1.5 mm² twin and earth on a 6 A device. They are wired either loop-in at the ceiling roses or through junction boxes. Many homes have one lighting circuit per floor, so a single fault does not leave the whole house dark.
What is a spur?
A spur is a branch taken off a ring. An unfused spur may feed only one single or one double socket. A fused spur, using a fused connection unit, can supply more points or a fixed appliance. The number of unfused spurs should not exceed the number of sockets and fixed appliances on the ring itself.
| Circuit | Typical cable | Typical protective device | Notes |
|---|---|---|---|
| Ring final (sockets) | 2.5 mm² twin and earth | 30 A or 32 A | Commonly serves a floor area up to about 100 m² |
| Radial (sockets) | 2.5 mm² or 4.0 mm² twin and earth | 20 A (2.5 mm²) or 32 A (4.0 mm²) | Commonly up to about 50 m² (20 A) or 75 m² (32 A) |
| Lighting | 1.0 mm² or 1.5 mm² twin and earth | 6 A (sometimes 10 A) | Radial, wired loop-in at roses or via junction boxes |
| Immersion heater | 2.5 mm² (heat-resistant flex at the heater) | 16 A | Dedicated radial with double-pole switch |
| Cooker or oven | 6.0 mm² or 10 mm² | 32 A to 45 A | Depends on appliance rating and cable route |
| Electric shower | 6.0 mm² to 16 mm² | 32 A to 50 A | Depends on shower kW, length and installation method |
Typical values only. The right cable and device depend on load, length, voltage drop, installation method and grouping, and must be designed to the current edition of BS 7671.
What does the consumer unit do?
The consumer unit, often still called the fuse box, is where the supply enters your wiring and splits into circuits. It holds the main switch, which isolates the whole installation, and a protective device for each circuit.
| Device | Protects against | Covers |
|---|---|---|
| MCB | Overload and short circuit | One circuit |
| RCD (RCCB) | Earth leakage (electric shock), usually 30 mA | A group of circuits in a split-load board |
| RCBO | Overload, short circuit and earth leakage | One circuit, so a fault only trips that circuit |
| SPD | Transient overvoltage (surges) | The whole installation |
Current regulations require 30 mA RCD protection on almost all domestic circuits, including sockets, lighting, bathroom circuits and cables buried in walls without other protection. Many new boards now use an RCBO on every way, so one fault does not take out several circuits at once.
Since 2016, domestic consumer units must have a non-combustible enclosure, usually steel, and surge protection is now expected in most new installations.
Dedicated appliance circuits and supply types
High-demand loads such as cookers, electric showers, immersion heaters and EV chargers each need their own radial circuit, with a larger cable and a higher-rated device. They also need a means of local isolation, such as a double-pole switch, for safe maintenance.
Single-phase or three-phase?
Nearly all UK and Irish homes have a single-phase supply at a nominal 230 V, with one line and one neutral. Three-phase at a nominal 400 V is normal in commercial and industrial buildings and is found in some larger homes, especially where heat pumps or multiple chargers are fitted.
What are earthing and bonding?
Earthing connects the exposed metal parts of the installation, such as metal accessories and appliance cases, to the main earthing terminal. If a live conductor touches them, a large fault current flows and the protective device disconnects quickly.
Main protective bonding connects incoming metal services, such as water and gas pipes, to the main earthing terminal. This stops a dangerous voltage appearing between metalwork you could touch at the same time. Main bonding conductors in homes are typically 10 mm², but the size depends on the supply.
| Earthing system | How it works | Where you see it |
|---|---|---|
| TN-C-S (PME) | Earth and neutral share a conductor in the supply network; the earth terminal is taken from the combined neutral | Most common in modern UK homes |
| TN-S | A separate earth, often the metal sheath of the supply cable | Older urban properties |
| TT | The installation has its own earth electrode (rod); RCDs are essential | Rural properties with overhead supplies |
In bathrooms, supplementary bonding can often be left out of modern installations if every circuit has 30 mA RCD protection and the main bonding is in place. An electrician must confirm this.
Safety: Never disconnect an earth or bonding conductor while the installation is energised. If you find a loose or missing earth clamp on a pipe, leave it and call an electrician.
Which cable types and sizes are used?
Most fixed house wiring is flat twin and earth cable (6242Y), with brown and blue insulated cores and a bare earth that is sleeved green/yellow at terminations. The earth is smaller than the live and neutral, as shown below.
| Twin and earth size | Earth (CPC) size | Typical domestic use |
|---|---|---|
| 1.0 mm² | 1.0 mm² | Lighting |
| 1.5 mm² | 1.0 mm² | Lighting, smoke alarms, fused spurs to small loads |
| 2.5 mm² | 1.5 mm² | Ring and radial socket circuits, immersion heaters |
| 4.0 mm² | 1.5 mm² | 32 A radials, some ovens |
| 6.0 mm² | 2.5 mm² | Cookers, smaller showers |
| 10 mm² | 4.0 mm² | Larger showers and cookers |
Typical values, not a design. Current-carrying capacity drops when cable passes through thermal insulation, is bunched with other cables or runs a long way. Your electrician sizes each circuit to BS 7671.
Other cable types in the home
- Three-core and earth: brown, black and grey cores, used for two-way lighting.
- Steel wire armoured (SWA): for outdoor and buried runs to garages, garden rooms and EV chargers.
- Fire-resistant cable: for fire alarm and emergency lighting circuits.
- Data and communication cable: low-voltage cabling for networks, kept separate from power cables.
For help choosing, see our guide to the best electrical cable for home wiring, or browse our full range of electrical cables.
Credit: Schneider Electric. Some terms and standards in this video may differ from UK practice.
When do you need an electrician?
Electrical work in UK homes must meet BS 7671. In England and Wales, Part P of the Building Regulations also makes some work notifiable to building control, which is usually done by a registered electrician who self-certifies. Notifiable work includes:
- Fitting a new circuit, such as a new socket radial, shower or EV charger circuit.
- Replacing a consumer unit.
- Adding to or altering a circuit in a bathroom or shower room (a special location).
The exact list differs slightly between England and Wales, and Scotland and Northern Ireland have their own building regulations, so check with building control if unsure. In the Republic of Ireland, most work beyond like-for-like replacement of accessories is restricted electrical work, which must be done and certified by a Registered Electrical Contractor.
Even non-notifiable work, such as replacing a damaged socket face, must be done safely and to BS 7671. If you are not sure, ask a qualified electrician.
Safety: Always isolate the circuit and prove it dead with an approved voltage indicator before touching any conductor. Inside a consumer unit, the incoming tails stay live even with the main switch off.
In short, UK house wiring basics come down to knowing the colours, understanding ring, radial and lighting circuits, and keeping the protection in your consumer unit up to date. Good knowledge makes you safer, but leave design, testing and certification to a registered electrician.
Key takeaways
- Current UK house wiring colours are brown (live), blue (neutral) and green/yellow (earth); before 2004 to 2006, red was live and black was neutral.
- Never identify a conductor by colour alone: isolate and test first.
- Ring final circuits feed most sockets, while radials feed lighting, cookers, showers and other big loads.
- MCBs protect cables, RCDs protect people, and RCBOs do both on a single circuit.
- Cable sizes in this guide are typical values; real designs follow BS 7671.
- New circuits and consumer unit changes are notifiable under Part P; in ROI they are work for a Registered Electrical Contractor.
Shop consumer units, protection and cable
Consumer units, MCBs, RCBOs and twin and earth cable for domestic installs. Trade prices, next working day delivery across NI & ROI on in-stock orders before 5pm.
Shop consumer units Shop twin and earthNeed help choosing? Call our team on 028 8675 1515 (048 from ROI), Monday to Friday, 8am–5pm.
FAQs
What are the UK house wiring colours?
Since harmonisation, UK house wiring uses brown for live, blue for neutral and green/yellow for earth. Homes wired before 2004 to 2006 usually have red for live and black for neutral, with green/yellow or plain green for earth. Three-phase wiring now uses brown, black and grey for the three line conductors.
When did UK wiring colours change?
The harmonised colours could be used from 31 March 2004 and became mandatory for all new work from 31 March 2006. Between those dates either system was allowed. An older installation does not need rewiring just because it has red and black cables, but mixed colours must be labelled at the consumer unit.
Is a black wire live or neutral in the UK?
It depends on the age and type of wiring. In pre-2004 single-phase wiring, black is usually neutral. In modern three-phase wiring, black is a line (live) conductor, and in lighting switch drops a black or blue core often carries switched live. Never assume: isolate and test every conductor first.
What is the difference between a ring and a radial circuit?
A ring final circuit leaves the consumer unit, loops round the sockets and returns to the same way, so current reaches each socket by two paths. It typically uses 2.5 mm² cable on a 32 A device. A radial circuit runs out and stops at the last point, as lighting, cooker and shower circuits do.
What size cable is used for sockets and lighting in a house?
Typical UK domestic practice is 2.5 mm² twin and earth for socket circuits and 1.0 mm² or 1.5 mm² for lighting circuits. These are typical values only. The correct size depends on the protective device, cable length, installation method, grouping and thermal insulation, so an electrician should confirm sizing to BS 7671.
Do I need an electrician to replace a consumer unit or add a circuit?
Yes. In England and Wales, replacing a consumer unit or adding a new circuit is notifiable under Part P, so use a registered electrician who can self-certify the work. In the Republic of Ireland this is restricted electrical work for a Registered Electrical Contractor. Either way, the work must be tested and certified.
How often should house wiring be checked?
An Electrical Installation Condition Report (EICR) is generally recommended at least every 10 years for an owner-occupied home and every 5 years for rented property. Private landlords in England must have one done at least every 5 years. Get the wiring checked sooner if you notice scorch marks, buzzing, burning smells or frequent tripping.