Electrical Wiring Colours Explained

Wiring Colours in the UK

In 2006, the wiring colour designations within the UK were harmonised with countries in mainland Europe to fulfil the specification of international standard IEC 60446. The standardisation of UK wiring colours was also covered in the second amendment of the 17th edition BS7671 Wiring Regulations for consistency and the avoidance of confusion. Wiring inspections are recommended in order to identify any deterioration and ensure compliance with the internationally recognised regulations.

The old colours of UK wiring were as follows:

• Black (neutral)

• Red (live)

• Green and yellow (earth)

It’s also worth noting that the earth wire was green prior to 1977.

Wiring Colour Codes

Changes to the wiring colour codes mean that fixed electrical and mains-powered cables (subsequent to the introduction of new cables) will feature the same colour wires as any flexible cabling. 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-style 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 path to the earth. However, this is prevented by the green and yellow earth wire as it effectively earths the electrical appliance.

There should be some warning signage indicating installations featuring circuits and/or fixed cables and wires of mixed colours. This warning should be very clearly designated on either the fuse board or the consumer unit.

UK Wiring Colours

The electrician should attach appropriately-coloured 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 style UK wiring colours, then the cables should be clearly marked to prevent the incorrect application of the phase and neutral.

There are varieties of cable within the UK with similar colouring to the 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 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’s 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. The three-phase connection is better suited to connection within workplaces featuring a variety of electrical machines and equipment, due to the increased generation of power. 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 don’t 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 difference between the new and old wire colours in the UK:

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 nationally-recognised code specifies that neutral wire should be of a white or grey colour, with green or green and yellow-striped patterning for the ground wire. Wiring colours in the USA may be categorised as either AC or DC supply.

The standard colouring of 120/208/240 Volt AC wiring is as follows:

• Phase 1 - Black

• Phase 2 - Red

• Phase 3 - Blue

• Neutral - White

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

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 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 wire

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

The standard DC colours are as follows:

• Positive (non-ground) - Red

• Negative (non-ground) - Black

• Ground - White or grey