Data reviewed: 20 October 2026 · Engineering Desk Tools · How we check calculations
Cable current carrying capacity in amps and watts
The current carrying capacity of a cable is the largest current it can carry continuously without its insulation overheating. It depends on the conductor (copper or aluminium), the insulation (PVC 70 °C or XLPE 90 °C), how the cable is installed and the ambient temperature. Use the lookup above for your exact case, or the tables below for quick values. To size a cable from a load and check voltage drop, use the cable size calculator.
House wiring: 1.5, 2.5, 4, 6, 10 and 16 sq mm wire load capacity
Values for copper PVC single-core wires in conduit with three loaded conductors (the conservative case). A single-phase circuit has two loaded conductors and can carry slightly more. Watts assume a resistive load (PF 1); for motors and air conditioners multiply by the power factor. The breaker must not be larger than the cable rating.
How to convert cable amps to watts
Single-phase: W = V × I × PF
Three-phase: W = √3 × V × I × PF
Example: a 2.5 mm² wire rated 21.8 A at 30 °C on 230 V carries 230 × 21.8 × 1 ≈ 5,000 W of heater load. For an air conditioner with PF 0.85 the same wire carries about 4,300 W.
Power cables: copper and aluminium current rating chart (16 to 630 mm²)
Source: Bahra Cables low voltage power cable catalogue; in ground to IEC 60287 at 0.5 m depth and soil resistivity 1.2 K·m/W, in air to BS 7671. Multi-core and armoured ratings are in the cable size calculator.
Temperature correction
The tables use hot-climate base conditions: 40 °C air and 35 °C ground. In cooler air a PVC cable can carry 15 % more at 30 °C (factor 1.15) and an XLPE cable 10 % more (factor 1.10). At 50 °C the factors fall to 0.82 for PVC and 0.90 for XLPE. The lookup applies these factors automatically.
About 1 mm² wire
1 mm² wire is mostly used for control circuits and small lighting loads and is not listed in the power cable catalogue used here. BS 7671 lists about 12 to 13.5 A for 1 mm² copper PVC wires in conduit at 30 °C; check the wire maker's datasheet before using it for power.
Cable capacity questions
What is the load capacity of 2.5 sq mm wire?
A 2.5 mm² copper PVC wire in conduit is rated about 19 A at 40 °C and about 22 A at 30 °C (three loaded conductors). On a 230 V single-phase supply that is roughly 4,400 to 5,000 W for a resistive load such as a heater. In practice it is used for socket circuits and appliances up to about 3.5 kW with a 16 A or 20 A breaker.
What is the current carrying capacity of 1.5 sq mm wire?
About 15 A at 40 °C and 17 A at 30 °C for copper PVC wire in conduit, which is roughly 3.5 to 4 kW at 230 V. It is normally used for lighting circuits protected by a 6 A or 10 A breaker.
How many watts can 4 sq mm and 6 sq mm wire carry?
In conduit at 30 °C, 4 mm² copper carries about 29 A (about 6,600 W at 230 V) and 6 mm² about 37 A (about 8,500 W). Long runs may need a bigger size to keep voltage drop low.
Which mm wire is required for a 1.5 ton AC?
A 1.5-ton split air conditioner draws roughly 7 to 10 A while running, so 2.5 mm² copper on its own circuit is the usual choice. Use 4 mm² for long runs, high ambient temperature or if the installation manual asks for it, and follow the breaker size given by the manufacturer.
What is the current carrying capacity of aluminium cable?
An aluminium conductor carries about 78 % of the current of a copper conductor of the same size. For example, three 95 mm² single-core XLPE cables in trefoil in free air are rated about 274 A in copper and 213 A in aluminium at 40 °C. Aluminium is normally used from 16 mm² upwards.
Why is the rating lower in conduit or at high temperature?
A cable is limited by how hot its insulation may get: 70 °C for PVC and 90 °C for XLPE. In conduit, in the ground or in hot air the heat escapes more slowly, so the same cable can carry less current. That is why ratings always state the installation method and ambient temperature.