Cable Size in Sydney (2026)

What a cable size costs in Sydney

A cable size calculator works out the right cable gauge, in square millimetres of conductor, for an electrical circuit from three things: the load it carries in amps, the length of the run, which causes voltage drop over distance, and the derating for how the cable is installed and how hot it gets. Undersizing a cable is dangerous, because an overloaded cable overheats and is a fire risk, while oversizing wastes copper, so the calculator finds the smallest safe gauge that carries the load without excessive voltage drop or heat.

Run length is a big factor in Sydney, because a long run from the switchboard to a granny flat behind a narrow eastern-suburbs terrace, a pool pump or a back-of-block workshop drops voltage, so the cable must be sized up a gauge or two to keep the voltage at the far end within limits, which a short run does not need. The ambient temperature and whether the cable runs through a roof space or is bundled derates its capacity, so a cable baking in a Sydney ceiling carries less than one in open air, and near the salt air of the coast the fittings and glands are chosen for durability too.

This is where a calculator stops and a licensed electrician starts, because in New South Wales it is illegal and dangerous for anyone but a licensed electrician to install or alter fixed wiring, so the calculator is a guide to understand the sizing, not a licence to do the work. The electrician sizes and installs the cable to the wiring rules under NSW Fair Trading. For a Sydney job, the clearest use of a cable size calculator is to enter the load, the run length and the install conditions, so you understand the gauge the electrician will use.