What are electrical wires?

Electrical wires are metallic conductors, usually copper, surrounded by insulating plastic, which carry electric current from the consumer unit to switches, sockets and appliances throughout a building. In the UK installation follows BS 7671 (the IET Wiring Regulations), which prescribe colour coding, cross-sections and routing.

Main cable types

Type	Application
Singles (H07V-U)	Fixed installation inside conduit, single core
Twin and earth (6242Y)	Fixed wiring in walls and ceilings
SWA cable	Buried or externally routed, steel armoured
Flexible cord (H05VV-F)	Connection to portable appliances
Low Smoke Halogen-Free	Fire-safe installation in escape routes

Colour coding

Under harmonised European colour codes:

Brown — line conductor L1 (230 V)
Black — line conductor L2
Grey — line conductor L3
Blue — neutral (N)
Green/yellow — protective earth (PE / earth)

Older UK installations used red (line) and black (neutral); always check before working.

Cross-section and protection

Typical conductor sizes in a dwelling:

Cross-section (mm²)	Max. current	Application
1.0	10 A	Lighting circuit
1.5	16 A	Lighting, low-power outlets
2.5	20 A	Ring/radial socket circuits
4.0	32 A	Cooker, immersion heater
6.0	40 A	High-power radials, supplies to outbuildings

Application and key points

Run in conduit — single-core conductors only inside conduit
Chase walls — vertical and horizontal zones close to sockets/switches
Earth required — for sockets in all wet rooms
RCD protection (30 mA) — mandatory on circuits supplying socket outlets
No mid-cable joints in walls — use junction boxes or approved connectors
Fire-stopping — depending on fire compartment

Extending or replacing

In refurbishment a quick survey of existing wiring is advisable. Older cable may have degraded insulation (rubber, lead) or insufficient earthing. An electrician will test to BS 7671.

Related terms

RCD
Earthing electrode
Consumer unit
Connected load
Earthing system

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