A Guide to Electrical Wiring Colours in the UK

Below are the old colours of UK wiring:

• Black (neutral)

• Red (live)

• Green and yellow (earth)

You should also note that prior to 1977, the earth wire was green.

If you would like to learn more about the current UK electrical wiring standards and BS 7671, you can visit our comprehensive electrical wiring regulations guide.

Wiring Colour Codes

Wiring colour code changes mean that fixed mains-powered and electrical cable (following the introduction of new wiring) and any flexible cabling now feature identical colour wires. The blue wire also referred to as the neutral wire, has the function of transferring electricity away from the appliance. The brown wire, otherwise known as the live wire, transfers electricity to the appliance. The combination of these wires is referred to as a circuit. You should be aware that some properties have old wiring, which should be regularly checked by an electrician to ensure that it remains in good working order. The need for replacement will be entirely dependent on the safety of the wiring.

The green and yellow wire is also referred to as the earth wire and has a key safety function. Electricity being transferred around any property will always take the path of least resistance to the earth. Damage to live or neutral wires could increase the risk of electrocution as the electricity may pass through the human body along its earthing path. However, this is prevented by the green and yellow earth wire as it effectively earths the electrical appliance.

Warning signage should be present to indicate fixed wires and cables of mixed colours and/or installations featuring circuits. This warning should be very clearly designated on either the fuse board, circuit breaker, distribution board, or consumer unit.

UK Wiring Colours

During a new installation, the electrician should attach appropriately-coloured insulation, sheathes, or sleeving to the different wires to enable easy identification of the corresponding wiring. As previously mentioned, the old-style black neutral wiring has been replaced with blue. Similarly, red live wiring is now brown. If there is any mixing of old and new wiring colours, then the cables should be clearly marked with the relevant colour codes to prevent the incorrect application of the phase and neutral.

Some cable varieties in the UK have similar colouring to mains wiring. As an example, TV aerial cables don’t carry any voltage but do have the same brown colour as the live mains cabling. It is also common to find black wire or cabling trailing behind the TV. This is the same colour as the old neutral wire. However, if there is any doubt, you should arrange for a professional electrician to carry out an inspection to ensure safety.

It is also important to be aware of the difference between single and three-phase wiring. The single-phase connection is formed of two wires, with the three-phase variety being formed of three or four wires. The single-phase connection allows for the relatively easy balancing of electrical loads via the network. Due to the increased power generation, the three-phase connection is better suited to connection within workplaces featuring a variety of electrical machines and equipment. You can identify either the two or three-phase connection by counting the wires connected with the electrical service panel.

A single-phase connection will feature dual black or red live wiring and blue neutral wiring. There is a voltage difference of 230V between the wires. Either three or four wires will be connected to an electrical service panel functioning via the three-phase system. This will feature three live wires of either a black, red, brown or grey colour and a separate blue wire. There will typically be a 400V separation between the two live wires. It is important that you do not make the mistake of confusing the natural blue and green/yellow earth connection when referring to the electrical system.

Old and New UK Wiring Colours

This handy chart highlights the differences between the new colours and old wiring colours in the UK:

3-Phase Colours in the UK

It is important to note that three-phase colours differ from the wiring colours used for standard wiring systems. 3-phase wiring colours were also harmonised in March 2006, meaning that United Kingdom standards are now more in line with three-phase wire practices across mainland Europe.

The old and new 3-phase colours can be seen in the table below:

USA Wiring Colours

In America, electricians and electrical contractors are legally required to comply with the National Electrical Code (NEC) for the colour coding of wires. This cable colour code is nationally-recognised and it specifies that neutral wire should be grey or white in colour, with green or a green-and-yellow-striped pattern for the ground wire. Wiring colours in the USA may be categorised as either AC or DC supply.

Standard 120/208/240 Volt AC wiring colouring is shown below:

• Phase 1 - Black

• Phase 2 - Red

• Phase 3 - Blue

• Neutral - White

• Ground - Bare wire, green, or green with yellow stripes

Such forms of wiring are commonly found within domestic and office environments. Systems featuring a single phase at a relatively high voltage should have orange wiring in reference to the high-leg connection. However, such high-leg systems are not typically found in modern electrical installations.

The standard colouring of 277/480 Volt AC wiring is as follows:

• Phase 1 - Brown

• Phase 2 - Orange

• Phase 3 - Yellow

• Neutral - Grey

• Ground - Green, green with yellow stripes, or bare

Finally, there is the direct current (DC) power wire colours, commonly featured in solar and battery power systems.

The standard DC cable colours are as follows:

• Positive (non-ground) - Red

• Negative (non-ground) - Black

• Ground - White or grey