AS/NZS 3008:2025 — What Engineers Need to Know

After eight years, AS/NZS 3008.1.1 has been updated. The 2025 edition — published in late 2024 by Standards Australia and Standards New Zealand — replaces the 2017 edition that has been the foundation of cable sizing practice across both countries. This article summarises the key changes that practising electrical engineers need to understand.

The update reflects significant developments in the electrical industry since 2017: the widespread adoption of solar PV systems, new cable constructions for fire safety, evolving IEC harmonisation, and updated research on thermal performance of cable installations. While the fundamental methodology remains the same, several tables and provisions have been revised.

The 2025 edition includes current rating data for cable constructions that have become prevalent since 2017:

• Low-Smoke Zero-Halogen (LSZH) cables: Increasingly required in public buildings, tunnels, and transport infrastructure. LSZH cables have different thermal characteristics than traditional PVC, and the 2025 edition provides specific current rating columns for common LSZH constructions.
• Fire-rated cables: Cables designed to maintain circuit integrity during fire exposure (per AS/NZS 3013) now have dedicated current rating data, rather than requiring engineers to interpolate or use manufacturer-specific data.
• High-voltage DC cables: With the growth of solar PV, battery energy storage, and EV charging, the demand for standardised DC cable selection has grown. While AS/NZS 3008.1.1 remains primarily an AC standard, the 2025 edition includes expanded guidance for DC applications.

These additions reduce reliance on manufacturer-specific datasheets and enable more standardised cable selection for modern installations.

The current rating tables (Tables 13, 14, and 15 in the 2017 edition) have been recalculated and, in some cases, restructured:

• Refined thermal modelling: The 2025 ratings are based on updated IEC 60287 thermal models with improved accuracy for multi-core cable constructions. Some ratings have increased slightly (typically 1–3%) where the 2017 values were found to be overly conservative.
• Table restructuring: Some installation method groupings have been reorganised to improve clarity and reduce the chance of column selection errors. Cross-references between the installation method table and the current rating tables have been made more explicit.
• Additional cable constructions: New columns for LSZH and fire-rated constructions mean the tables are broader, with more cable types covered directly rather than requiring interpolation.

Several derating factor tables have been updated based on research conducted since 2017:

• Grouping factors (Table 25 equivalent): Updated values for cables on perforated trays and in enclosed trenches, based on thermal imaging studies of real installations. The changes generally result in slightly less conservative factors for well-ventilated tray installations and slightly more conservative factors for cables in enclosed trenches where ventilation is restricted.
• Soil thermal resistivity: The range of tabulated soil types has been expanded, with more granular data for Australian and New Zealand soil conditions. New guidance is provided for seasonally variable soil conditions (e.g., soil that is moist in winter but dry in summer).
• Direct sunlight exposure: The solar radiation guidance has been clarified with a more explicit methodology, aligning with IEC 60364-5-52 Amendment 1. The recommended temperature adder for cables in direct sunlight has been refined from a general “approximately 15°C” to specific values based on cable colour and geographic location.

A key driver of the 2025 update is closer alignment with IEC 60364-5-52, the international cable selection standard:

• Installation method descriptions: The 29 installation methods in AS/NZS 3008 Table 3 have been cross-referenced to the IEC method codes (A1, B1, C, D, E, F, G) in a new mapping table. This makes it significantly easier for engineers working on international projects to translate between the two standards.
• Derating factor presentation: The format of derating factor tables has been brought closer to the IEC presentation style, with consistent column headings and factor ranges. The underlying values remain specific to Australian/NZ conditions (particularly the 40°C reference ambient), but the table structure is now more recognisable to engineers familiar with IEC 60364.
• Voltage drop methodology: The mV/A/m voltage drop calculation approach is unchanged, but the impedance data tables have been aligned with IEC 60228 conductor data for standard sizes, improving consistency with international calculations.

This harmonisation is particularly valuable for Australian engineering firms working on international projects and for international firms tendering for work in Australia and New Zealand.

Reflecting the explosive growth of solar PV in both Australia and New Zealand, the 2025 edition includes new guidance specifically for PV installations:

• DC string cables: Guidance for selecting DC cables connecting PV modules to the string inverter, including temperature derating for rooftop installations where ambient temperatures at module level can exceed 70°C in summer.
• Combined AC/DC cable routes: Provisions for derating when DC solar cables share containment systems with AC distribution cables — a common practical scenario in commercial and industrial installations.
• Temperature considerations: Recognition that rooftop ambient temperatures are significantly higher than ground-level ambient, with recommended temperature adders for rooftop installations based on roof colour and cable mounting height above the roof surface.

These provisions align with AS/NZS 5033 (Installation and safety requirements for photovoltaic arrays) and reduce the need for separate PV-specific cable sizing guidance.

The transition from the 2017 to the 2025 edition follows the typical Australian standards adoption process:

1. Publication (late 2024): The 2025 edition is published and available for use. Both the 2017 and 2025 editions are valid.
2. Voluntary adoption period (2025–2026): Engineers can choose to use either edition. New designs may reference either standard.
3. Mandatory adoption (expected 2026–2027): When the next edition of AS/NZS 3000 (Wiring Rules) is published, it will reference AS/NZS 3008:2025. At that point, the 2025 edition becomes mandatory for all new installations in jurisdictions that adopt the updated Wiring Rules.

During the transition period, it is recommended to:

• Use the 2025 edition for all new designs where possible, to future-proof calculations
• Not re-calculate existing designs unless the installation has not yet been constructed
• Note which edition was used on all design documentation and reports
• Check with your local regulator for jurisdiction-specific transition dates — some states (e.g., Victoria via Energy Safe Victoria) may mandate adoption earlier than others

During the transition period, engineers should have access to both the 2017 and 2025 edition table data. This allows direct comparison of the same circuit under both editions, identifying where the new edition produces different cable selections and understanding the impact on specific designs.

A practical approach is to calculate critical circuits under both editions and document the differences. This reveals which installation scenarios are most affected by the table changes and helps prioritise which existing designs to review.

All engineering reports should clearly state which edition was used, satisfying documentation requirements during the transition period.