澳大利亚内陆高温环境（45°C或50°C以上）电缆降容系数详解
Cable Derating Factors for Ambient Temperatures Exceeding 45°C or 50°C in the Australian Outback
澳大利亚内陆高温环境（45°C或50°C以上）电缆降容系数详解
Anhui Feichun Special Cable Co., Ltd. 安徽飞纯特种电缆有限公司
1. Introduction: The Challenge of Extreme Heat 引言：极端高温的挑战
The Australian Outback presents one of the most demanding thermal environments for electrical cable installations worldwide. Mining operations in the Pilbara region of Western Australia regularly experience ambient temperatures exceeding 45°C, with record temperatures reaching 50.7°C at Onslow in January 2022—equalling Australia’s all-time temperature record. These extreme conditions necessitate careful application of derating factors to ensure cable integrity and operational safety. 澳大利亚内陆地区是全球电缆安装最具热挑战性的环境之一。西澳大利亚Pilbara地区的采矿作业经常面临超过45°C的环境温度，2022年1月Onslow曾记录到50.7°C的创纪录高温——与澳大利亚历史最高温度持平。这些极端条件需要仔细应用降容系数以确保电缆完整性和运营安全。
The Australian Standard AS/NZS 3008.1.1:2017 provides the authoritative framework for cable selection and derating in Australian installation conditions. Unlike many international standards that assume 30°C ambient temperature, AS/NZS 3008 uses 40°C as the baseline for cables installed in air—acknowledging Australia’s hotter climate. However, temperatures in the Outback frequently exceed even this elevated baseline. 澳大利亚标准AS/NZS 3008.1.1:2017为澳大利亚安装条件下的电缆选择和降容提供了权威框架。与许多假设30°C环境温度的国际标准不同，AS/NZS 3008使用40°C作为空气中安装电缆的基准——这承认了澳大利亚更炎热的气候。然而，内陆地区的温度经常超过这一已经提高的基准。
2. Understanding Derating Fundamentals 降容基础原理
2.1 What is Cable Derating? 什么是电缆降容？
Cable derating reduces the current-carrying capacity (ampacity) of a cable to account for installation conditions that differ from standard reference conditions. The fundamental principle is thermal management: a cable’s insulation has a maximum permissible operating temperature, and as ambient temperature rises, less heat can be dissipated, requiring a reduction in current to prevent insulation damage. 电缆降容是减少电缆的载流能力（安培容量），以考虑与标准参考条件不同的安装条件。基本原理是热管理：电缆绝缘有最高允许工作温度，随着环境温度升高，散热能力下降，需要降低电流以防止绝缘损坏。
Maximum Continuous Operating Temperatures 最高连续运行温度
- PVC (V-75): 75°C conductor temperature 导体温度75°C
- PVC (V-90): 90°C conductor temperature 导体温度90°C
- XLPE (X-90): 90°C conductor temperature 导体温度90°C
- EPR/HEPR (R-EP-90): 90°C conductor temperature 导体温度90°C
- XLPE (X-HF-110): 110°C conductor temperature 导体温度110°C
- Silicone Rubber: 180°C conductor temperature 导体温度180°C
2.2 The Derating Formula 降容公式
The derated current-carrying capacity is calculated by multiplying the tabulated base rating by all applicable correction factors: 降容后的载流能力通过将表格中的基础额定值乘以所有适用的校正系数来计算：
Where IZ is the derated current-carrying capacity, Itable is the tabulated base rating from AS/NZS 3008.1.1, and k factors are the various correction coefficients. 其中IZ是降容后的载流能力，Itable是AS/NZS 3008.1.1表格中的基础额定值，k系数是各种校正系数。
3. AS/NZS 3008.1.1 Table 27(1): Air Temperature Derating Factors AS/NZS 3008.1.1表27(1)：空气温度降容系数
Table 27(1) of AS/NZS 3008.1.1:2017 provides correction factors for cables installed in air at ambient temperatures other than the standard 40°C (for Australian conditions). These factors are critical for Outback installations. AS/NZS 3008.1.1:2017的表27(1)提供了在非标准40°C环境温度（澳大利亚条件）下空气中安装电缆的校正系数。这些系数对内陆安装至关重要。
| Ambient Temp (°C) 环境温度 | Maximum Conductor Operating Temperature 最高导体运行温度 | ||||
|---|---|---|---|---|---|
| 60°C | 75°C | 80°C | 90°C | 110°C | |
| 35 | 1.12 | 1.07 | 1.06 | 1.04 | 1.03 |
| 40 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| 45 | 0.87 | 0.93 | 0.94 | 0.96 | 0.97 |
| 50 | 0.71 | 0.85 | 0.87 | 0.88 | 0.94 |
| 55 | 0.50 | 0.76 | 0.79 | 0.82 | 0.90 |
| 60 | — | 0.65 | 0.71 | 0.75 | 0.87 |
| 65 | — | 0.50 | 0.61 | 0.67 | 0.83 |
| 70 | — | — | 0.50 | 0.58 | 0.79 |
| 75 | — | — | — | 0.47 | 0.75 |
| 80 | — | — | — | — | 0.71 |
Note: “—” indicates the ambient temperature exceeds the conductor’s maximum operating temperature, making the cable unsuitable for that condition. 注：”—”表示环境温度超过导体最高运行温度，电缆不适用于该条件。
Critical Observation: At 50°C ambient temperature, a PVC-75 cable (75°C rated) must be derated to only 85% of its tabulated capacity, while an XLPE-90 cable retains 88% capacity. At 55°C, PVC-75 drops to 76% while XLPE-90 maintains 82%. This demonstrates the significant advantage of higher-rated insulation in extreme heat environments. 关键观察：在50°C环境温度下，PVC-75电缆（75°C额定）必须降容至表格容量的85%，而XLPE-90电缆保持88%容量。在55°C时，PVC-75降至76%，而XLPE-90保持82%。这表明高额定绝缘材料在极端高温环境中的显著优势。
4. Direct Sunlight Exposure: Additional 20°C Consideration 阳光直射：额外20°C考虑因素
According to Clause 3.5.8 of AS/NZS 3008.1.1, cables exposed to direct sunlight require special consideration. The standard recommends applying an additional 20°C to the ambient temperature when selecting derating factors for sun-exposed installations. 根据AS/NZS 3008.1.1第3.5.8条款，直接暴露在阳光下的电缆需要特别考虑。标准建议在为阳光暴露安装选择降容系数时，在环境温度基础上增加20°C。
⚠️ Critical for Outback Installations: In the Pilbara during summer, ambient air temperature of 45°C combined with direct sunlight exposure means engineers should use derating factors for 65°C (45°C + 20°C). A cable surface temperature measurement in full sun can exceed 80°C even when ambient air is 50°C. ⚠️ 内陆安装关键提示：在Pilbara夏季，45°C的环境空气温度加上阳光直射意味着工程师应使用65°C的降容系数（45°C + 20°C）。即使环境空气温度为50°C，阳光直射下的电缆表面温度测量值也可能超过80°C。
| Ambient Air (°C) 环境空气 | Effective Temp with Sun (°C) 阳光下有效温度 | XLPE-90 Factor XLPE-90系数 | PVC-75 Factor PVC-75系数 | Capacity Loss 容量损失 |
|---|---|---|---|---|
| 40 | 60 | 0.75 | 0.65 | 25–35% |
| 45 | 65 | 0.67 | 0.50 | 33–50% |
| 50 | 70 | 0.58 | — | 42%+ (XLPE only) |
| 55 | 75 | 0.47 | — | 53%+ (XLPE only) |
5. AS/NZS 3008.1.1 Table 27(2): Soil Temperature Derating Factors AS/NZS 3008.1.1表27(2)：土壤温度降容系数
For buried cables, the reference soil temperature in Australia is 25°C. In the Outback, soil temperatures can significantly exceed this, particularly at shallow depths in summer. Table 27(2) provides the applicable correction factors. 对于埋地电缆，澳大利亚的参考土壤温度为25°C。在内陆地区，土壤温度可能显著超过此值，特别是夏季浅层土壤。表27(2)提供了适用的校正系数。
| Soil Temp (°C) 土壤温度 | Maximum Conductor Operating Temperature 最高导体运行温度 | |||
|---|---|---|---|---|
| 75°C | 80°C | 90°C | 110°C | |
| 25 | 1.00 | 1.00 | 1.00 | 1.00 |
| 30 | 0.96 | 0.97 | 0.97 | 0.98 |
| 35 | 0.92 | 0.93 | 0.94 | 0.96 |
| 40 | 0.87 | 0.89 | 0.91 | 0.94 |
| 45 | 0.82 | 0.84 | 0.87 | 0.92 |
| 50 | 0.76 | 0.79 | 0.84 | 0.89 |
6. Additional Derating Factors: Tables 28 and 29 附加降容系数：表28和表29
6.1 Depth of Burial (Table 28) 埋设深度（表28）
The standard burial depth in AS/NZS 3008.1.1 is 0.5 metres. Cables buried deeper experience reduced heat dissipation and require additional derating. AS/NZS 3008.1.1中的标准埋设深度为0.5米。埋设更深的电缆散热减少，需要额外降容。
| Depth (m) 深度 | Derating Factor 降容系数 |
|---|---|
| 0.5 | 1.00 |
| 0.8 | 0.98 |
| 1.0 | 0.96 |
| 1.5 | 0.93 |
| 2.0 | 0.90 |
6.2 Soil Thermal Resistivity (Table 29) 土壤热阻率（表29）
The standard soil thermal resistivity is 1.2 K·m/W. Dry, sandy Outback soils typically have higher resistivity (1.5–2.5 K·m/W), requiring additional derating. Drought conditions can increase resistivity dramatically due to soil moisture loss. 标准土壤热阻率为1.2 K·m/W。干燥的内陆沙质土壤通常具有更高的热阻率（1.5-2.5 K·m/W），需要额外降容。干旱条件会因土壤水分流失而大幅增加热阻率。
| Thermal Resistivity (K·m/W) 热阻率 | Typical Soil Type 典型土壤类型 | Derating Factor 降容系数 |
|---|---|---|
| 0.8 | Wet clay 湿粘土 | 1.09 |
| 1.2 | Standard reference 标准参考 | 1.00 |
| 1.5 | Damp sand 潮湿沙土 | 0.94 |
| 2.0 | Dry sand 干燥沙土 | 0.86 |
| 2.5 | Very dry, stony 极干燥、多石 | 0.80 |
| 3.0 | Drought conditions 干旱条件 | 0.75 |
7. Worked Example: Pilbara Mining Installation 计算实例：Pilbara采矿安装
Scenario 场景
A 3-phase circuit requires 85 A at an iron ore mine in the Pilbara. The cable will be installed in air on cable trays, partially exposed to direct sunlight. Design ambient temperature: 50°C (summer conditions).
Pilbara某铁矿的三相电路需要85A电流。电缆将安装在电缆桥架上的空气中，部分暴露在阳光直射下。设计环境温度：50°C（夏季条件）。
Step 1: Determine Effective Temperature 步骤1：确定有效温度
With direct sunlight exposure, add 20°C: Effective temperature = 50°C + 20°C = 70°C
Step 2: Select Cable Type and Derating Factor 步骤2：选择电缆类型和降容系数
From Table 27(1) at 70°C ambient:
- PVC-75: Not suitable (ambient exceeds rating)
- XLPE-90: Derating factor = 0.58
- XLPE-110: Derating factor = 0.79
Step 3: Calculate Required Base Rating 步骤3：计算所需基础额定值
Step 4: Select Cable Size 步骤4：选择电缆规格
From AS/NZS 3008.1.1 Table 14 (3-core XLPE, copper, unenclosed spaced from surface):
- XLPE-90: 35 mm² (base rating 158 A) provides adequate margin
- XLPE-110: 25 mm² (base rating 116 A) would be sufficient
Recommendation: For this extreme environment, select 35 mm² XLPE-90 cable or consider upgrading to XLPE-110 rated cable (X-HF-110) which allows a smaller 25 mm² conductor while providing greater thermal margin for safety. 建议：对于这种极端环境，选择35 mm² XLPE-90电缆，或考虑升级到XLPE-110额定电缆（X-HF-110），该电缆允许使用更小的25 mm²导体，同时提供更大的热安全裕度。
8. Cable Selection Recommendations for Outback Conditions 内陆条件电缆选型建议
| Application 应用 | Recommended Insulation 推荐绝缘 | Rationale 理由 |
|---|---|---|
| Surface mining (exposed) 露天采矿（裸露） |
EPR-90 or XLPE-110 R-EP-90 / X-HF-110 |
Superior UV resistance, higher thermal margin |
| Underground mining 地下采矿 |
EPR-90 with CPE sheath R-EP-90 + CPE护套 |
Flexibility, flame retardance, mechanical durability |
| Mobile equipment trailing cables 移动设备拖曳电缆 |
EPR-90 or CSP-90 R-EP-90 / R-CSP-90 |
Flexibility, abrasion resistance, oil resistance |
| Solar PV arrays 光伏阵列 |
XLPE-90UV or TÜV certified PV cable X-90UV / TÜV认证光伏电缆 |
UV stability, DC rated, 25+ year lifespan |
| Buried distribution 埋地配电 |
XLPE-90 armoured X-90铠装 |
Mechanical protection, thermal stability in soil |
| Extreme heat (>60°C ambient) 极端高温（>60°C环境） |
Silicone rubber or XLPE-110 硅橡胶或X-HF-110 |
Maximum thermal headroom |
Best Practices for Extreme Heat Installations 极端高温安装最佳实践
- Use UV-stabilised cable (black outer sheath with carbon black content ≥2%)
- Install cables in shaded cable trays where possible
- Maintain adequate spacing between cables to maximise heat dissipation
- For buried cables, use thermal backfill to reduce soil thermal resistivity
- Allow 10–15% additional margin above calculated derating requirements
- Document design ambient temperature assumptions for future reference
- Consider time-of-day load profiles—peak loads may coincide with peak temperatures
9. Comparison: AS/NZS 3008 vs IEC 60364-5-52 比较：AS/NZS 3008与IEC 60364-5-52
Engineers working on international projects should note the differences between Australian and IEC standards: 从事国际项目的工程师应注意澳大利亚标准和IEC标准之间的差异：
| Parameter 参数 | AS/NZS 3008.1.1 (Australia) 澳大利亚 | IEC 60364-5-52 (International) 国际 |
|---|---|---|
| Reference air temperature 参考空气温度 | 40°C | 30°C |
| Reference soil temperature 参考土壤温度 | 25°C | 20°C |
| Reference burial depth 参考埋设深度 | 0.5 m | 0.7 m |
| Reference soil resistivity 参考土壤热阻率 | 1.2 K·m/W | 2.5 K·m/W |
Due to Australia’s higher reference temperatures, the base current ratings in AS/NZS 3008 are generally lower than equivalent IEC tables. Do not mix tables from different standards without applying appropriate conversion factors. 由于澳大利亚的参考温度较高，AS/NZS 3008中的基础额定电流通常低于等效的IEC表格。不要在不应用适当转换系数的情况下混用不同标准的表格。
References and External Resources 参考文献和外部资源
- Standards Australia. AS/NZS 3008.1.1:2017 “Electrical installations—Selection of cables—Part 1.1: Cables for alternating voltages up to and including 0.6/1 kV—Typical Australian installation conditions” standards.org.au
- Standards Australia. AS/NZS 3000:2018 “Electrical installations (known as the Australian/New Zealand Wiring Rules)”
- IEC 60364-5-52:2009+AMD1:2024 “Low-voltage electrical installations—Part 5-52: Selection and erection of electrical equipment—Wiring systems” webstore.iec.ch
- ELEK Software. “Cable Current Rating Derating Factors Explained.” elek.com
- ELEK Software. “Effect of Direct Sunlight to Cable Size (AS/NZS 3008.1).” support.elek.com
- Global Solar Energy Solutions (GSES). “DC Cable Sizing using AS/NZS 3008.” gses.com.au
- Cleantech Controls. “Calculating the Current-Carrying Capacity of a Cable.” cleantechcontrols.com.au
- Cleantech Controls. “AS/NZS 3008 – What Are the Best Practices for Cable Sizing?” cleantechcontrols.com.au
- Bureau of Meteorology (Australia). Climate statistics for Pilbara region. bom.gov.au
- Sudmeyer, R (2016). “Climate in the Pilbara.” Bulletin 4873, Department of Agriculture and Food, Western Australia. library.dpird.wa.gov.au
- The Conversation. “This WA town just topped 50°C – a dangerous temperature many Australians will have to get used to.” theconversation.com
- Schneider Electric. “Electrical Installation Guide: General method for cable sizing.” electrical-installation.org
- jCalc.net. “Cable Size Calculator AS/NZS 3008.” jcalc.net
- SparkyCalc. “AS/NZS 3008 Cable Sizing Calculator.” sparkycalc.com
Contact Anhui Feichun Special Cable Co., Ltd. 联系安徽飞纯特种电缆有限公司
For technical enquiries regarding high-temperature cables, mining cables, and cable selection for Australian Outback conditions, please contact our engineering team: 如需有关高温电缆、矿用电缆和澳大利亚内陆条件电缆选型的技术咨询，请联系我们的工程团队：