Table 27 of AS/NZS 3008.1 gives the correction factor (derating factor in 2017) for temperature. It moves a cable rating from the reference temperature to the real site. Table 27(1) covers air, and Table 27(2) covers soil.
The 2025 edition of the Australian part splits and renumbers it. In AS/NZS 3008.1.1:2025, air is Table 3.44 and soil is Table 3.45. AS/NZS 3008.1.2:2017, the New Zealand part, numbers them Tables 27(1) and 27(2).
This page explains the table. It shows no values from it. The calculator reads the values for you.
What the rows and columns mean
Each row is one conductor temperature, set by the insulation. PVC runs at up to 75 °C, and XLPE at up to 90 °C. Each column is an air or soil temperature. The cell is the factor.
The 2025 air table has rows for 75 °C, 80 °C, 90 °C, 110 °C and 150 °C conductors. Its columns run from 15 °C to 140 °C. Cl 3.5.3 sets out when the factor applies.
The reference temperature
The factor is 1 at the reference temperature. Above it, the factor is less than 1. Below it, the factor is more than 1.
- The Australian part has a reference of 40 °C air and 25 °C soil.
- The New Zealand part has a reference of 30 °C air and 15 °C soil.
AS/NZS 3000:2018 Cl 3.3.2.1 sets the same reference air temperatures by country. Use the factors of one part only with the ratings of that part. The guide on the 2025 edition runs a 45 °C case on both editions.
How to read the table in the calculator
- Set the Standard select. AU reads AS/NZS 3008.1.1, and NZ reads AS/NZS 3008.1.2:2017.
- For AU, set the Edition select to 2017 or 2025.
- Enter the ambient temperature. For a buried method, the field is the soil temperature.
- Pick the insulation. It selects the row.
The result shows the factor as a step, with the table it read. The candidate table shows each size before and after correction.
One circuit on both editions
The inputs are 230 V single phase, 42 A and 20 m. The cable is multicore copper with PVC insulation, unenclosed and touching, in air at 50 °C.
- 2017: Table 27(1) gives a correction factor of 0.82. 10 mm² carries 41.82 A, less than 42 A. The calculator selects 16 mm² at 55.76 A.
- 2025: Table 3.44 gives 0.85. 10 mm² carries 43.35 A and passes. The calculator selects 10 mm², with a drop of 1.49 %.
Open on 2017 and open on 2025.
What changed in 2025
- The numbers. Table 27(1) is now Table 3.44, and Table 27(2) is now Table 3.45.
- The method. The IEC 60364-5-52 method now derives the air and soil factors.
- Hot air. Above 40 °C, the air factors reduce a rating less than in 2017.
- Cool air. Below 40 °C, the air factors add the same or a little less than in 2017.
- Soil. Some soil factors change. The soil table adds rows for 80 °C and 110 °C conductors.
The table number map gives the 2025 number of every table that AmpSize reads. The learn page on derating explains how the temperature factor combines with the others. The glossary defines the reference ambient.
For New Zealand, AmpSize reads AS/NZS 3008.1.2:2017 and its Tables 27(1) and 27(2).
This page is a design aid. Verify every value against the current edition of the standard.