Cable Size
Find the smallest cable size that passes each check.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the cable size calculator do?
The tool tests every standard conductor size in turn. It checks the derated current capacity, the voltage drop, the protective device rating, the earth fault loop impedance and the fault withstand. It reports the smallest size that passes every check. Sizes that fail are listed with the check that failed.
Which standard and tables does the result come from?
Current ratings come from AS/NZS 3008.1.2:2017 Tables 4 to 21. Reactance comes from Table 30 and a.c. resistance from Tables 34 and 35. Derating comes from Tables 22 and 25 to 29. The k factor comes from Table 52. Earth size and maximum Zs come from AS/NZS 3000:2018 Tables 5.1 and 8.1. Selection follows Clause 3.4.
What size cable do I need for a 63 A circuit in New Zealand?
Enter 63 A as the design current. Then enter the run length, the installation method, the ambient temperature and the number of grouped circuits. The tool derates the tabulated rating and applies the voltage drop limit. The answer changes with the route, so no single size suits every 63 A circuit.
How do the derating factors work?
The tool multiplies the ambient, grouping, soil and burial depth factors into one factor. It divides the design current by that factor to get the required tabulated current. Soil resistivity and burial depth apply only to buried methods. Grouping applies when more than one circuit shares the route.
Does the tool use Australian tables, and can I share a result?
No. New Zealand conditions are the default and the data comes from AS/NZS 3008.1.2. The AS/NZS 3008.1.1 tables used in Australia are not included yet. Every input sits in the page address, so you can copy the link to share a design. Saving a calculation to a project needs an account.