Electric Cable Types & Sizes for the Home

Choosing the wrong cable for a domestic circuit is not simply a code violation, undersized conductors overheat under load, damaging insulation and creating fire risk. Oversized cables cost more and can be hard to terminate in accessories designed for smaller conductors. Getting cable selection right means understanding current-carrying capacity, installation method, and the correction factors that apply to your specific situation.

This guide covers the cable types used in UK domestic wiring, their current ratings, and typical applications, all referenced to BS 7671 (the 18th Edition Wiring Regulations). The current version is BS 7671:2018+A4:2026; the previous amendment, A3:2024, can be used only until 15 October 2026.¹

The Most Common Cable Types

Twin and Earth (TWE): Flat Grey PVC

The standard cable for fixed wiring throughout a UK house. A flat PVC sheath contains two insulated conductors (live in brown, neutral in blue) and an uninsulated bare earth conductor. The earth must be sleeved green-and-yellow where exposed.

Manufacturer designation: 6242Y (twin and earth, PVC insulated, PVC sheathed).

Typical applications:

• Lighting circuits: 1 mm² or 1.5 mm²
• Socket ring mains: 2.5 mm²
• Cooker/oven circuits: 6 mm² or 10 mm²
• Shower circuits: 6 mm² or 10 mm²

Meter tails, from the meter to the consumer unit, are not twin and earth: they are single-core double-insulated cable, usually 16 mm² or 25 mm².

Three-Core and Earth

Used where a switch-wire return is needed, commonly in two-way lighting circuits, ceiling fans with separate light/fan controls, and some appliance connections. Conductors are brown, black, grey and a bare earth; where the black and grey carry line current, as in two-way switching, they should be sleeved or taped brown.

Steel Wire Armoured (SWA)

SWA cable has individual XLPE or PVC insulated cores, a bedding layer, steel wire armour, and an outer PVC sheath. It can be buried directly in the ground, clipped to external surfaces, or run in areas where mechanical damage is a risk. The armour itself can serve as the earth conductor in many installations, though a separate earth is safer practice.

Typical domestic uses: sub-mains to outbuildings, garden power, buried runs to garages and sheds.

Flexible Cable (Flex)

Flexible cable uses finely stranded conductors to allow repeated bending without conductor fatigue, used for appliance connections, extension leads, and pendant lighting. It must not be used for fixed wiring buried in walls or chased into plaster.

Common flex types:

• 2182Y, two-core light duty flex for table lamps, radios and similar light unearthed appliances²
• 3182Y, two-core round flex²
• 3183Y, three-core, the usual flex for earthed household appliances such as washing machines and fridges²
• 3093Y (heat-resistant PVC) and 3183TQ (heat-resistant rubber), three-core flexes for hot locations²

MICC (Mineral Insulated Copper Clad)

A copper tube filled with magnesium oxide powder encasing copper conductors, extremely fire-resistant and mechanically robust. Used in commercial fire-alarm circuits, escape lighting, and boiler rooms. Rare in ordinary domestic work but occasionally specified in kitchens or plant rooms.

Current Ratings and Cable Sizing

Current ratings in BS 7671 depend on the installation method (clipped to surface, enclosed in insulation, in conduit, buried, etc.) and correction factors for ambient temperature, grouping with other cables, and thermal insulation proximity.

The table below gives simplified reference ratings for common twin-and-earth cables in domestic use, assuming installation method C (clipped direct to a non-thermally insulating surface) and no grouping or insulation correction required:

These clipped-direct figures match makers’ published ratings for 6242Y twin and earth, from 16 A for 1.0 mm² to 85 A for 16 mm², the largest size it is made in.²

Important: these figures are indicative. Cables buried in thermal insulation (e.g., within a wall cavity or under loft insulation) require a significant derating, sometimes as low as 0.5× of the clipped rating. Always apply the appropriate BS 7671 correction factors or use an approved design tool.

Sizing by Circuit Type

Lighting Circuits

Most domestic lighting circuits are wired in 1.5 mm² twin-and-earth, protected by a 6 A or 10 A MCB. At 230 V, a 6 A circuit can carry about 1,380 W and a 10 A circuit about 2,300 W. LED lamp loads are so low that a single circuit can serve a whole floor in most houses, the traditional practice of limiting to 8–10 outlets (assuming 100 W per lamp) is largely obsolete.

Socket Ring Mains

The standard domestic socket circuit is a ring main wired in 2.5 mm² twin-and-earth, protected by a 30 A or 32 A device (in a modern consumer unit, an MCB or RCBO). Each leg of the ring must be continuous; spurs are permitted but limited, and a fused spur is taken through a fused connection unit with a BS 1362 fuse. IET guidance still uses the rule of thumb that one ring should serve a floor area of no more than 100 m².³

Cooker Circuits

A cooker circuit is radial and sized to the demand of the appliance. IET guidance (the On-Site Guide) gives a diversity allowance:

• First 10 A of demand + 30 % of remainder + 5 A if a socket outlet is included in the cooker control unit.

In practice, most 10–13 kW electric ranges are wired in 6 mm² on a 32 A MCB, or 10 mm² on a 40 A MCB for induction ranges or large range-cookers.

Electric Shower Circuits

Shower circuits are radial, dedicated, and sized to the shower’s rated power:

Cable size also depends on run length and installation method. Shower makers typically call for a double-pole isolating switch, commonly rated 45 A, within easy reach; inside the bathroom this is normally a ceiling pull-cord switch, since other switches must be kept out of the bathroom zones.

EV Charger Circuits

A standard 7.4 kW (32 A) home EV charger is usually wired in 6 mm² cable on a dedicated circuit. Its RCD must be Type B, unless the charger itself provides protection against DC fault current, in which case a Type A or Type F RCD can be used.⁴ On voltage drop alone, 6 mm² at 32 A stays within the 5 % limit for runs up to about 49 m (11.5 V ÷ (7.3 mV/A/m × 32 A)); 10 mm² is needed on longer runs or where the installation method derates the cable.

Voltage Drop

For an installation supplied from the public network, BS 7671 treats 3 % for lighting and 5 % for other circuits as acceptable voltage drop under normal load. For long cable runs, to an outbuilding or across a large house, voltage drop may dictate a larger conductor than the current-carrying capacity alone would require. Use the formula:

V-drop (mV) = (mV/A/m from BS 7671 Table) × current (A) × length (m) ÷ 1,000

Table values for twin and earth are 18 mV/A/m for 2.5 mm² and 7.3 mV/A/m for 6 mm².⁵

Material Costs (Per Metre, Mid-2026)

Prices vary by supplier and quantity. Trade account holders at builders’ merchants usually pay less than the listed prices.

Key Rules to Remember

• Three things are notifiable under Part P of the Building Regulations: a new circuit, a consumer unit replacement, and an addition or alteration inside a bathroom’s special location, the zone running from floor level to 2.25 m and 0.6 m out from the bath or shower tray, or 1.2 m from the shower head where there is no tray. Adding to an existing circuit anywhere else, kitchens and outdoor work included, is not notifiable, though it must still comply with BS 7671.⁷
• Cable buried less than 50 mm deep in a wall must run in a safe zone, within 150 mm of the top of the wall or of a corner, or horizontally or vertically in line with an accessory, unless it is mechanically protected or has an earthed metal covering.⁸ Cables concealed less than 50 mm deep also need 30 mA RCD protection.⁹
• Do not mix aluminium and copper conductors without an approved mechanical connector, galvanic corrosion at the joint causes resistance heating.
• Always label all circuits clearly at the consumer unit after completing work; label direction of travel if cables are concealed.

If you are not a registered competent person yourself, have all new circuit work and consumer unit changes carried out and certified by one before signing off on any building project.