Electrical Wire Sizes and Colours: A Practical Guide

When preparing first-fix electrical materials for a villa, building or shop, two questions come up again and again: which wire size suits each circuit, and which colour is used for each conductor? This guide gives a practical answer to help you read the drawings and prepare your material order — the design engineer and the Saudi Building Code remain the final reference.

How are electrical wires sized?

Wire size is the cross-sectional area of the copper conductor in square millimetres (mm²), not the outside diameter with insulation. The larger the cross-section, the more current the wire can carry. That capacity also depends on the installation method (in conduit, surface or buried), how many wires share a conduit, ambient temperature and run length.

Common wire sizes and typical uses

Cross-section	Typical use	Breaker often used*
1.5 mm²	Lighting circuits	10 A
2.5 mm²	General socket circuits	16 – 20 A
4 mm²	Water heaters and some AC units	25 A
6 mm²	Larger AC units, cookers and higher loads	32 A
10 mm² and above	Sub-main and main board feeders	Per load and design

* Guidance values only, for insulated copper wires in conduit under normal conditions. The actual rating is set by the engineer or licensed electrician after calculating load, voltage drop and installation method.

Electrical wire colours

The international colour code used in current standards (including those followed by the Saudi Building Code) identifies conductors as follows:

Conductor	Colour
Phase (line) in single-phase circuits	Brown
Three phases L1 / L2 / L3	Brown / Black / Grey
Neutral	Blue
Earth (protective conductor)	Green with yellow stripe

Older installations may use different colours, such as red, yellow and blue for phases and black for neutral. Never rely on colour alone when working on existing wiring — always test before starting work.

Tips when ordering wire for a project

• Order from the cable schedule on the drawings, stating size, colour and length or number of drums for each size.
• Keep colours consistent across the whole project to make future maintenance easier.
• Allow a sensible margin for waste and terminations, especially on long runs.
• Mention any brand or specification approved by the consultant.

See the cable types we supply on our cables and wires page, and read our guide to circuit breaker types to choose the right breaker.