How do I size a cable for an Australian installation?

Australian cable sizing follows AS/NZS 3008.1.1:2025 and AS/NZS 3000:2018. Every cable must pass three checks. (1) Current carrying capacity: the cable must safely carry the full load current after derating for ambient temperature, grouping, and installation method. (2) Voltage drop: total drop from source to load must not exceed 5% of nominal voltage (AS/NZS 3000 Clause 3.6). (3) Earth fault loop impedance: the loop must be low enough for protection to clear faults within Table 5.1 disconnection times. The calculator runs all three in parallel and returns the smallest size that passes.

What is the maximum voltage drop allowed in AS/NZS 3000?

AS/NZS 3000:2018 Clause 3.6 sets the limit at 5% of the nominal supply voltage from the point of supply to the most remote point of the installation. For 230 V single-phase that is 11.5 V; for 400 V three-phase line-to-line that is 20 V. Some industries and supply authorities require tighter limits (3% is common for sensitive equipment). Set the target percentage in the calculator and it back-solves to the cable size that just passes.

How is current carrying capacity determined?

Current carrying capacity (Iz) starts from the base current rating in AS/NZS 3008.1.1:2025 tables for the chosen cable construction (PVC, XLPE, copper, aluminium) and installation method. Three derating factors then apply: ambient temperature (default 40 °C in Australia), grouping (number of circuits in the same enclosure), and depth of burial for direct-buried cables. Iz = Itable × Ka × Kg × Kd. The calculator does this automatically based on the inputs you provide.

What changed in AS/NZS 3008.1.1:2025 compared to 2017?

The 4th edition (December 2025) updates the current rating tables with newer cable constructions, revises grouping derating for closely-packed installations, expands installation methods to include solar PV DC string circuits and EV charging infrastructure, and adjusts ambient temperature reference values to better reflect Australian conditions. Some 2017 cable sizes will calculate slightly differently in 2025; the calculator uses the 2025 tables throughout.

Does the calculator handle parallel cables and multiple circuits per conduit?

Yes. Set the grouping factor in the inputs to reflect the number of loaded circuits in the same enclosure or on the same tray. The calculator applies the AS/NZS 3008.1.1 grouping derating automatically. For parallel cables, divide the design current by the number of cables in parallel and size each leg.

Can I use this for cables longer than 100 m?

Yes. The calculator handles any length. For very long runs, voltage drop is usually the binding constraint rather than current carrying capacity. The calculator will return a cable size large enough to keep the drop under your selected limit, which may be much larger than current rating alone would require.

AS/NZS 3008.1.1:2025

Cable Sizing Calculator

Free Australian cable sizing calculator covering current rating, voltage drop, and earth fault loop impedance per AS/NZS 3008.1.1:2025. Mobile-first, no login.

Inputs

Phase Configuration

Load Current (A)

Cable Run Length (m)

Protection Device Rating (A)

Installation Method

▶Advanced options

Max Voltage Drop (%)

AS/NZS 3000:2018 default limit is 5%

Ambient Temperature (°C)

Number of Circuits in Group

Results

Recommended Cable Size

2.5

mm² copper

Earth: 2.5 mm²

Current Carrying Capacity

23 A (>= 20 A)

Voltage Drop

4.6 % (<= 5 %)

Protection Device ≤ Cable Capacity

20 A (<= 23 A)

Combined Derating Factor1

Derated Current Capacity23 A

Actual Voltage Drop10.64 V (4.6%)

Important: These results are indicative only. Cable sizing tables are pending CPEng validation against AS/NZS 3008.1.1:2025. Do not use for final design without independent verification.

Cable Sizing Guide

Cable sizing in Australia is governed by AS/NZS 3008.1.1:2025 (Australian conditions) and AS/NZS 3000:2018 (Wiring Rules). The 4th edition was published in December 2025 and introduces updated current rating tables, revised derating factors, and expanded coverage for modern installation methods including solar PV DC circuits.

The three checks every cable must pass

1
Current carrying capacity : The cable must carry the full load current continuously without exceeding its rated temperature.
2
Voltage drop : Voltage drop from source to load must not exceed 5% of the nominal supply voltage (AS/NZS 3000 Clause 3.6).
3
Earth fault loop impedance : Total earth fault loop impedance must be low enough that the protection device disconnects within the required time.

Disclaimer: This calculator is provided as a guide only and must be verified by a qualified electrical engineer before use in design or installation. Always refer to the current edition of AS/NZS 3008.1.1 and AS/NZS 3000.

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