Get a starting point for cable sizing: the smallest standard conductor that keeps voltage drop within limits for your load and run — then confirm current-carrying capacity to the standards.
This sizes for voltage drop only. You must also confirm the cable’s current-carrying capacity for your installation method, grouping and ambient temperature using AS/NZS 3008 — that may require a larger size.
traqR keeps the quote, job and compliance paperwork for each electrical job together — so what you spec on site is what ends up on the invoice.
Start free trialYour allowable drop (usually 5%) times the supply voltage gives the maximum volts you can lose across the run.
Rearranging the voltage-drop formula gives the minimum cross-sectional area that keeps the run within that budget, then we round up to the next standard size.
Voltage drop is only half the job. The cable must also carry the load current safely under its installation conditions — always confirm against AS/NZS 3008.
Cable selection has to satisfy several things at once: current-carrying capacity for the installation conditions, voltage drop within limits, protection against fault currents, and earth loop impedance. This tool covers the voltage-drop part and suggests the smallest standard conductor that passes it — but the final size is the largest required by any of those checks.
No — it sizes for voltage drop only. The current a cable can safely carry depends on its insulation, how it’s installed (in conduit, buried, on a tray), how many cables are grouped together and the ambient temperature. Those are covered by the derating tables in AS/NZS 3008 and can call for a larger cable than voltage drop alone.
Common conductor sizes step through 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50 mm² and up. This tool rounds the calculated minimum up to the next size in that series, since you can’t buy an arbitrary cross-section.
No. It’s an indicative starting point. Compliant cable sizing must be designed and verified by a licensed electrician against AS/NZS 3000 and AS/NZS 3008, accounting for all the factors above and your specific installation.
This calculator is an indicative aid that sizes for voltage drop only, using approximate resistivity values. It does not determine current-carrying capacity, fault protection or earthing requirements. Cable selection must be designed and verified by a licensed electrician to AS/NZS 3000 and AS/NZS 3008.
traqR keeps each electrical job’s spec, quote and compliance paperwork together. Try it free for 14 days.