Myth: AS/NZS and IEC Give the Same Result for the Same Installation

“AS/NZS 3008 is based on IEC 60364, so they give the same cable size. Just use whichever tables you have handy.”

This assumption appears in engineering offices across the Asia-Pacific region, where projects may reference AS/NZS domestically and IEC internationally. It is wrong, and it leads to cables that are either oversized (wasting copper) or undersized (risking failure).

While AS/NZS 3008.1.1:2017 shares DNA with IEC 60364-5-52, the two standards diverge in several critical areas:

The ambient temperature difference is the most significant. AS/NZS uses 40°C as the reference because Australian conditions are hotter than the European baseline. This means the base ratings in AS/NZS tables are lower for the same cable — they already assume a hotter environment. When you apply temperature correction factors, the results diverge further depending on the actual site temperature.

Scenario: 50mm² 4-core Cu/XLPE cable, installed on a perforated cable tray with 6 circuits grouped together, actual ambient temperature 35°C.

Under AS/NZS 3008.1.1:2017

• Base rating (Table 4, Column 17, perforated tray, touching): 110A
• Temperature correction for 35°C (Table 27, ref 40°C, max 90°C): × 1.07
• Grouping factor for 6 circuits (Table 22, perforated tray): × 0.73
• Derated capacity: 110 × 1.07 × 0.73 = 85.9A

Under IEC 60364-5-52:2009

• Base rating (Table B.52.5, method E, perforated tray): 125A
• Temperature correction for 35°C (Table B.52.14, ref 30°C, max 90°C): × 0.96
• Grouping factor for 6 circuits (Table B.52.17, single layer, touching): × 0.72
• Derated capacity: 125 × 0.96 × 0.72 = 86.4A

In this example, the results happen to be close (85.9A vs 86.4A — less than 1% difference). But change the ambient to 25°C:

• AS/NZS: 110 × 1.20 × 0.73 = 96.4A (cooler than reference, so capacity increases)
• IEC: 125 × 1.04 × 0.72 = 93.6A (slightly cooler than reference, small increase)

At 50°C ambient:

• AS/NZS: 110 × 0.89 × 0.73 = 71.5A
• IEC: 125 × 0.82 × 0.72 = 73.8A

The differences range from negligible to over 10% depending on conditions. At extreme ambient temperatures (common in Middle Eastern, African, and Australian projects), the gap widens further.

The standards are not interchangeable. The correct approach:

• Identify the governing standard from the project specification, local regulations, or client requirements.
• Use that standard’s tables exclusively — do not mix AS/NZS base ratings with IEC correction factors.
• When comparing across standards (e.g., checking an IEC-designed system against AS/NZS for an Australian installation), run the full calculation under each standard independently and compare the final derated values.

“Based on IEC” does not mean “identical to IEC.” The national adaptations exist because local conditions, practices, and safety philosophies differ. Respect those differences.