AS/NZS 3008.1.1 Cable Sizing — Method
AS/NZS 3008.1.1:2017 is the joint Australia / New Zealand standard for cable selection and ampacity, used together with AS/NZS 3000:2018 (the Wiring Rules). The method mirrors IEC 60364-5-52 — pick a cable whose tabulated Iz ≥ Ib after Ca, Cg, Ci correction — but tables are recalculated for V75/V90/X-90 insulations and Australian ambient (typically 40 °C reference). Voltage drop limit is 5 % from main switchboard to the load.
Where:
- Ib — design current of the circuit (A), from the load calculation
- Ca — ambient temperature correction (1.00 at 30 °C reference)
- Cg — grouping / bunching factor (1.00 for a single circuit)
- Ci — thermal-insulation factor (1.00 if the cable is in free air; 0.50 if fully buried in insulation)
Then pick the smallest cable cross-section in AS/NZS 3008.1.1 Table 4 / Column 11 (75 °C V90 thermoplastic, in conduit) whose tabulated ampacity Iz ≥ It.
Related cable sizing calculators
Other standard- and method-specific cable-sizing calculators in the same series — same procedure, different reference tables and defaults:
- Cable Sizing Calculator (universal) — the seed page covering all standards in one tool
- IEC 60364 Cable Sizing Calculator — IEC 60364-5-52 · International
- BS 7671 Cable Sizing Calculator — BS 7671:2018+A2 · UK / NICEIC
- Three-Phase Cable Sizing Calculator — Three-Phase · 400 V / 415 V / 480 V
- All Electrical Engineering Calculators →
💡 Sizing the earth / protective conductor? Use the dedicated Earthing Cable Size Calculator — BS 7671 Table 54.7, IEC 60364-5-54, NEC 250.122.
Frequently Asked Questions
AS/NZS 3000:2018 is the Wiring Rules — the regulatory standard saying what is allowed (clearances, RCD requirements, equipotential bonding, 5 % voltage-drop limit). AS/NZS 3008.1.1:2017 is the cable selection standard — the look-up tables and methods that tell you which cable size satisfies AS/NZS 3000's electrical requirements. Together they replace the older AS 3008 and SAA Wiring Rules.
Tables 3, 4, 5, 6 of AS/NZS 3008.1.1 give current-carrying capacities for copper conductors with V75, V90, R-HF-90 and X-90 insulations; Tables 9–12 do the same for aluminium. Each table has columns for installation conditions A–T (in air, in conduit, on tray, buried, etc.). The reference ambient for Aus is 40 °C above ground and 25 °C below ground (NZ uses 30 °C above).
40 °C for cables installed in air (above ground) and 25 °C for cables direct-buried below ground. New Zealand uses 30 °C for above-ground cables. If the actual ambient differs, apply Ca from Table 27 (e.g. 0.91 at 45 °C, 0.82 at 50 °C for V90 insulation in air).
Vd = Vc × I × L / 1000, where Vc is the conductor 'mV/A·m' value from Tables 40–47, I is the design current and L is the run length. AS/NZS 3000 Clause 3.6 caps Vd at 5 % of nominal voltage between the point of supply and any consumer outlet. For three-phase circuits use the line-to-line value of Vc.
AS/NZS 3008.1.1 Section 5 / Equation 5.1: t × I_sc² ≤ K² × S² where K = 111 (V75 Cu), 143 (X-90 Cu), 74 (V75 Al), 94 (X-90 Al), I_sc is the prospective short-circuit current and t is the protective device's clearing time. The selected cable must satisfy both ampacity and short-circuit withstand.
Methodology yes (Iz × Ca × Cg × Ci ≥ Ib), tables no. AS/NZS uses different reference ambients (40 °C vs 30 °C), different installation-condition labels (A–T vs A1–E) and different K values for short-circuit. A cable sized to AS/NZS 3008 is generally accepted in IEC jurisdictions, but not necessarily vice-versa — always size to the local code.