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Cable Sizing Calculator per AS/NZS 3008.1.1:2017 for Australia

AS/NZS 3008.1.1:20172017Australia

Cable sizing in Australia follows AS/NZS 3008.1.1:2017. Engineers determine conductor sizes using Table 3 current-carrying capacities for V-75 and X-90 insulation types, apply derating factors from Table 22 (ambient temperature), Table 23 (soil thermal resistivity), and Table 24 (grouping), then verify voltage drop against AS/NZS 3000:2018 limits of 5% from point of supply.

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Quick Reference Table

Australian Cable Sizing Key References — AS/NZS 3008 — AS/NZS 3008.1.1:2017 (2017)
ParameterValue / RequirementClause Reference
Supply voltage230 V single-phase / 400 V three-phaseAS/NZS 3000:2018, Clause 1.4.4
Frequency50 HzAS/NZS 3000:2018, Clause 1.4.4
Current-carrying capacity (V-75)PVC insulated cables at 75 °C conductor temperatureAS/NZS 3008.1.1, Table 3, Column 5-12
Current-carrying capacity (X-90)XLPE insulated cables at 90 °C conductor temperatureAS/NZS 3008.1.1, Table 3, Column 13-20
Voltage drop limit5% from point of supply to any point in the installationAS/NZS 3000:2018, Clause 3.6.2
Ambient temperature correctionFactors for ambient temperatures from 25 °C to 80 °CAS/NZS 3008.1.1, Table 22
Common conductor sizes1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50 mm²AS/NZS 3008.1.1, Table 3
Installation methodsEnclosed, unenclosed, buried — 21 columns per insulation typeAS/NZS 3008.1.1, Table 3 & Table 13

How to Calculate Cable Sizing for Australia

  1. 1

    Determine the design current

    Calculate maximum demand per AS/NZS 3000 Part 2. For domestic, apply Table C1 diversity factors. For commercial/industrial, use assessed load.

  2. 2

    Select insulation type and installation method

    Choose cable insulation (V-75 PVC or X-90 XLPE) and installation method from AS/NZS 3008.1.1 Table 3 — enclosed in conduit, on tray, clipped to surface, or direct buried.

  3. 3

    Apply Australian derating factors

    Apply ambient temperature correction (Table 22), soil thermal resistivity (Table 23 for buried cables), and grouping factors (Table 24). Australian ambient temperatures can reach 40-50 °C in outback locations.

  4. 4

    Select cable size from Table 3

    Find the smallest conductor size in Table 3 with a derated current-carrying capacity equal to or greater than the design current divided by the product of derating factors.

  5. 5

    Verify voltage drop per AS/NZS 3000

    Calculate voltage drop using Table 35-42 values (mV/A/m). Total drop from the point of supply must not exceed 5% (11.5 V at 230 V) per AS/NZS 3000 Clause 3.6.2.

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Run compliant AS/NZS 3008.1.1:2017 calculations for australia — free, instant results with full clause references.

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BS 7671 vs AS/NZS 3008 Cable Sizing Comparison

ParameterBS 7671AS/NZS 3008
RegionUnited KingdomAustralia & New Zealand
Voltage drop limit3% lighting / 5% other5% general (AS/NZS 3000 Table C7)
Reference ambient temp30°C air40°C air (Table 22)
Ampacity tablesAppendix 4 Tables 4D1A–4J4ATables 13–20 (by method)
Derating tablesCa, Cg, Ci, Cc factorsTables 22, 24, 25, 26 factors
Soil temp reference20°C25°C (Table 25)
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Frequently Asked Questions

For a 20 A circuit using V-75 PVC cable clipped direct in ambient up to 40 °C, you need at least 2.5 mm² per AS/NZS 3008.1.1 Table 3. However, at 45 °C ambient, the derating factor from Table 22 may push the selection to 4 mm². Always verify voltage drop for runs over 20 m.
Australia and the UK both use metric mm² sizes (1.5, 2.5, 4, 6, 10 mm², etc.). However, current ratings differ significantly because AS/NZS 3008.1.1 uses a 40 °C ambient reference (in many columns) while BS 7671 uses 30 °C. The same 2.5 mm² cable may have different ratings under each standard.
Australia's high ambient temperatures significantly impact cable sizing. In Darwin or outback regions where ambient reaches 45-50 °C, AS/NZS 3008.1.1 Table 22 derating factors can reduce cable capacity by 15-25%, often requiring one or two sizes larger than the same circuit in a temperate UK climate.

Related Guides

Cable Sizing — AS/NZS 3008.1.1:2017

New Zealand

Cable Sizing — AS/NZS 3008.1.1:2017

Residential Installations

Cable Sizing — BS 7671:2018+A2

United Kingdom