AS/NZS 3008:2025 vs 2017 — 7 Changes That Affect Every Cable Calculation

AS/NZS 3008.1.1:2025 has been published, replacing the 2017 edition that has been the foundation of cable sizing practice in Australia and New Zealand for eight years. If you're still calculating to the 2017 edition, your calculations remain valid for existing installations — but for new designs, it's time to update.

Having worked with both editions extensively (and implemented both in ECalPro's calculation engine), here are the 7 changes that will affect the most calculations. Some are obvious, others are subtle but significant.

Change 1: Expanded DC Cable Ratings (Up to 1500V DC)

The 2017 edition covered DC applications up to 750V DC. The 2025 edition expands coverage to 1500V DC, reflecting the rapid adoption of high-voltage DC systems in:

• Solar PV installations — string voltages on commercial arrays commonly reach 1000–1500V DC
• Battery energy storage systems (BESS) — DC bus voltages of 800–1500V DC
• EV DC fast charging — up to 1000V DC for CCS/CHAdeMO
• DC distribution — emerging DC microgrids in data centres and industrial facilities

The new DC tables include ratings for both single-core and multicore cables in common installation methods, with derating factors specific to DC circuits. DC cables don't experience AC effects (skin effect, proximity effect), so DC current ratings are slightly different from AC ratings for the same cable construction.

AS/NZS 3008.1.1:2025, Section 5 — DC cable selection

Change 2: Updated Installation Method Classifications

The 2017 edition defined 29 installation methods in Table 3 (numbered 1–29). The 2025 edition has reorganised and expanded these to improve alignment with IEC 60364-5-52.

Key changes:

• New mapping table cross-referencing AS/NZS installation method numbers to IEC reference method codes (A1, A2, B1, B2, C, D1, D2, E, F, G)
• Several installation methods have been renumbered or regrouped for clarity
• New installation methods added for cables on mesh trays and cables in enclosed ventilated trays — reflecting modern cable management systems that didn't have specific entries in the 2017 edition
• More explicit descriptions of each method, reducing the ambiguity that led to incorrect method selection

The IEC cross-reference is particularly valuable for international firms working across multiple standards. An engineer familiar with IEC Method E can now directly identify the equivalent AS/NZS method number.

Change 3: Revised Current Rating Tables

The current rating tables (Tables 13, 14, and 15 in the 2017 edition) have been recalculated based on updated IEC 60287 thermal models:

• Most common cable types (V-90 PVC, X-90 XLPE): changes are minor — typically 1–3 A difference from the 2017 values. Some ratings have increased slightly where the 2017 values were found to be overly conservative.

• New cable constructions added: LSZH (Low Smoke Zero Halogen) and fire-rated cables now have dedicated current rating columns. Previously, engineers had to interpolate from similar cable types or use manufacturer data.

• Table structure reorganised: cross-references between the installation method table and the current rating tables have been made more explicit, reducing the risk of column selection errors.

For the vast majority of standard calculations using V-90 or X-90 cables, the results will be identical or within one standard cable size. The tables are evolutionary, not revolutionary.

AS/NZS 3008.1.1:2025, Tables 13-15 — Current-carrying capacity

Change 4: Updated Grouping Derating Factors

The grouping correction factors (Table 25 in the 2017 edition) have been revised based on thermal imaging research conducted since 2017:

The changes reflect real-world thermal measurements. Well-ventilated perforated trays dissipate heat more effectively than the 2017 models assumed, allowing slightly higher cable ratings. Enclosed trunking, where ventilation is restricted, is now treated slightly more conservatively.

For most practical calculations, the changes are within 5% — rarely enough to change a cable size selection. But for borderline calculations where the margin is tight, the 2025 factors should be used.

Change 5: Enhanced Thermal Insulation Requirements

The 2025 edition includes expanded guidance on cables passing through or in contact with thermal insulation — a increasingly common scenario in energy-efficient buildings.

Key updates:

• More specific derating values for different insulation thicknesses and cable positions (surrounded vs. one side in contact)
• New clause addressing cables in thermally insulated walls with limited ventilation
• Alignment with the approach in BS 7671 Section 523 for cables in thermally insulated walls

AS/NZS 3008.1.1:2025, Clause 3.5 — Thermal insulation derating

The practical impact: cables that pass through insulated ceiling spaces, wall cavities, or under-floor insulation may need to be derated more than previously required. Engineers designing residential and commercial buildings with high thermal performance (as required by NCC 2025 energy efficiency provisions) need to pay particular attention to this change.

Change 6: Expanded Soil Thermal Resistivity Data

For buried cables, the soil thermal resistivity significantly affects the cable's ability to dissipate heat. The 2017 edition assumed a reference soil resistivity of 1.2 K·m/W with limited data for other soil types.

The 2025 edition provides:

• Expanded soil type tables with more granular data for Australian and New Zealand soil conditions
• Seasonal variation guidance — recognition that soil in many Australian regions is moist in winter but dry in summer, with significantly different thermal resistivity in each season
• Recommended values by geographic region — for the first time, the standard provides guidance on typical soil resistivity ranges for different parts of Australia (e.g., sandy coastal, clay inland, rocky mining regions)

This change is particularly relevant for:

• Solar farm DC cable arrays (typically direct buried)
• Power distribution in mining regions with variable soil conditions
• Underground cable routes in regional and outback areas

Change 7: Solar Radiation and Rooftop Temperature Corrections

The 2017 edition included a general note that cables exposed to direct sunlight should be derated, with an approximate 15°C temperature adder. The 2025 edition refines this with:

• Specific temperature adders by cable colour: dark-coloured cables absorb more solar radiation than light-coloured cables
• Geographic corrections: solar radiation intensity varies significantly across Australia (e.g., Darwin vs Hobart)
• Rooftop installation guidance: cables on rooftops operate in ambient temperatures that can be 15–25°C above ground-level ambient, depending on roof colour, cable mounting height, and time of day

AS/NZS 3008.1.1:2025, Clause 3.4 — Temperature correction including solar radiation

This change directly impacts solar PV installations, where DC cables on rooftops and in unventilated roof spaces have historically been one of the most commonly undersized cable applications.

Transition Timeline

Both the 2017 and 2025 editions are currently valid. The transition follows the standard Australian pattern:

1. 2024–2025: Publication and voluntary adoption
2. 2025–2026: Transition period — either edition may be used
3. 2026–2027: Mandatory adoption expected when the next edition of AS/NZS 3000 references the 2025 edition

What to Do Now

1. Obtain a copy of AS/NZS 3008.1.1:2025 from Standards Australia
2. Update your calculation tools — spreadsheets, software, and templates that reference 2017 table data
3. Verify installation method numbers if your tools reference specific method numbers
4. Review any buried cable designs against the updated soil thermal resistivity data
5. Check rooftop PV installations against the new solar radiation correction factors
6. Note the edition on all calculation reports — this is essential during the transition period

ECalPro supports both AS/NZS 3008:2017 and AS/NZS 3008:2025, allowing engineers to compare results between editions for the same circuit.

Related Resources

• Cable Sizing: The 50m Office Feeder — How AS/NZS compares to BS, IEC, and NEC
• The Complete Cable Sizing Comparison — All AS/NZS derating factors vs other standards
• Grenfell Tower: Fire-Resistant Cable Sizing — Cable sizing worked example using BS 7671
• View all standards comparisons →