Where are 1.5 mm², 2.5 mm², 4 mm² and 6 mm² cables used?
What are 1.5, 2.5, 4 and 6 mm² cables used for?
Quick answer: In copper building wiring, 1.5 mm² is commonly used for lighting, while 2.5 mm² is a familiar choice for many radial socket circuits. Sizes of 4 mm² and 6 mm² are often considered for dedicated appliance supplies and smaller distribution feeders. These are typical applications, rather than fixed rules. A cable’s safe current rating depends on how and where it is installed.
The mm² marking specifies the nominal cross-sectional area of each conductor. It does not describe the cable’s outside diameter or the combined area of all its cores. A cable marked 3 × 2.5 mm² has three cores, each with a nominal conductor area of 2.5 mm². The examples below concern copper conductors; they should not be applied directly to aluminium cables.
Typical applications at a glance
| Conductor size | Typical uses | What may change the choice? |
|---|---|---|
| 1.5 mm² | Lighting circuits and some low-current fixed supplies. | Long runs, numerous fittings, driver inrush current and routes through thermal insulation. |
| 2.5 mm² | Many radial socket circuits and some dedicated appliance circuits. | Simultaneous loads, sustained demand, cable length and grouping with other loaded cables. |
| 4 mm² | Higher-current appliance supplies, some motor or pump circuits and smaller feeders. | Single-phase or three-phase supply, motor nameplate current, starting conditions and voltage drop. |
| 6 mm² | Some cooker, heater and other higher-power circuits, plus smaller distribution board supplies, where calculations confirm suitability. | Appliance connections, total demand, cable route and temperature. A larger size may be required. |
Wiring practices and circuit arrangements differ between countries. The applicable installation rules, circuit design and equipment instructions determine the final choice. When using a current-carrying capacity table, check the cable construction and installation method it covers before relying on its figures.
1.5 mm²: A common lighting size
A lighting circuit usually has a very different load from an electric heater. The fact that 1.5 mm² is widely used for lighting does not make it suitable for any appliance connected nearby. LED lighting also needs more than a wattage check: switching several drivers on together can produce a brief but substantial inrush current. Circuit length and the protective device’s characteristics matter too.
2.5 mm²: Socket circuits need a load assessment
Finding 2.5 mm² cable on a socket circuit does not mean every outlet can supply a large load at once. A heater, kettle and another appliance operating together all contribute to the circuit’s demand. Where an appliance requires a dedicated supply, plugging it into an existing socket circuit may be unsuitable even if the conductor size initially looks adequate.
A 3,000 W resistive heater draws about 13 A at 230 V: I = P / U = 3,000 / 230. That establishes the approximate load current; it does not complete the cable selection. The plug, socket, terminations, cable route and circuit protection must also be suitable for the load.
4 mm² and 6 mm²: Check the actual equipment
There is no universal rule that an oven needs 4 mm² or a hob needs 6 mm². Appliances differ in rated power and may have different single-phase or three-phase connection options. Follow the manufacturer’s supply requirements and assess the proposed circuit. A feeder supplying several circuits also needs an assessment of the overall demand, rather than the rating of one appliance.
For motors and pumps, kW alone is not enough. Use the motor’s nameplate current, duty, starting method and protection requirements. The simple P / U calculation used for a resistive heater cannot be applied directly to a motor’s mechanical output rating.
Why the same load may need a larger cable
A longer cable run produces more voltage drop. Heat dissipation also changes when a cable is installed in conduit, surrounded by insulation, exposed to higher temperatures or grouped with other loaded circuits. A size that works for a short run under favourable conditions may therefore be unsuitable for a longer or hotter route.
For example, take a single-phase copper circuit carrying 16 A over a one-way distance of 25 metres. Using an approximate copper resistivity of 0.0175 Ω·mm²/m at 20 °C and assuming a resistive load, the voltage drop is about 5.6 V with 2.5 mm² and 3.5 V with 4 mm². Both outgoing and return conductors are included. This compares voltage drop only; current-carrying capacity still needs a separate check. Resistance increases as the conductor heats up. See voltage drop in long cable runs for a closer look.
Cable size and circuit protection must work together
The protective device must suit the cable’s current-carrying capacity under the actual installation conditions. A circuit may include smaller conductors or components with lower ratings elsewhere along its route. If a breaker trips, fitting a higher-rated breaker without investigating the load and circuit can leave those parts inadequately protected. Cable selection also involves short-circuit withstand and the required disconnection time. The cable sizing guide explains the design checks in more detail.
The right size still needs the right cable and terminals
A 6 mm² marking does not establish suitability for outdoor use, direct burial or repeated movement. Insulation, sheath and mechanical properties must match the application. Check outdoor and underground cable requirements separately from the choice between solid and stranded conductors.
Never trim strands to force a conductor into an undersized terminal. Doing so reduces the conductor area and compromises the connection. Use terminals approved for the conductor size and class, the correct ferrule where required, and the specified tightening torque. A hot termination can be caused by poor contact even when the cable itself is correctly sized.
If a cable or connection overheats or smells burnt: Stop using the circuit. Isolate the supply if you can do so safely and have a qualified electrician inspect the wiring and protection. A breaker that has not tripped does not prove that every connection is safe.