Current-carrying capacity (ampere capacity) is a core parameter for medium voltage cable selection, system design, and safe operation. For cross-linked polyethylene (XLPE) insulated medium voltage cables (6kV–35kV), current-carrying capacity directly determines conductor temperature rise, insulation life, short-circuit withstand capability, and system stability. This document, based on the IEC 60287 standard, IEEE research, and field engineering data, elucidates key influencing factors, engineering derating rules, practical parameters, and real-world project applications to support accurate design and reliable operation.
Current carrying capacity refers to the maximum continuous current that a cable can carry under specified installation conditions, without exceeding the temperature limit of the insulation material. For cross-linked polyethylene (XLPE) medium-voltage cables:
Continuous operating temperature: 90°C
Short-circuit temperature: 250°C (maximum 5 seconds)
Calculation standard: IEC 60287 series
Research by IEC and IEEE confirms that external thermal environments can cause cable temperature rise by up to 70%, therefore, environment and laying method are the most critical factors.
- At the same cross-sectional area, copper (Cu) has a 20% higher current carrying capacity than aluminum (Al).
- A larger cross-sectional area reduces resistance and improves heat dissipation.
- Standard cross-sectional areas for medium-voltage cables: 25mm², 35mm², 50mm², 70mm², 95mm², 120mm², 150mm², 185mm², 240mm², 300mm².
- XLPE has higher temperature resistance and better thermal stability.
- Higher heat resistance = higher permissible current carrying capacity.
- All medium-voltage cables must use XLPE insulation (IEC 60502 / GB/T 12706).
- Air laying: Optimal heat dissipation → highest current carrying capacity. Direct burial: Affected by soil conditions → Reduced current carrying capacity.
- Pipes, trenches, or dense bundling: Poor heat dissipation → Requires derating.
- High ambient temperature → Reduced current carrying capacity.
- High soil thermal resistance (dry, sandy): Poor heat dissipation → Significantly reduced current carrying capacity.
- High soil moisture can improve heat dissipation and slightly increase current carrying capacity.
- Tightly laid multiple cables can cause mutual heating.
- Current carrying capacity derating factor: 0.8–0.95, the specific value depends on the number of cables and spacing.
- Armoring structures slightly reduce heat dissipation.
- Confined spaces and poor ventilation reduce current carrying capacity.
Ambient Temperature: 25°C | Soil Thermal Resistance: 1.0 K·m/W
|
Type |
Voltage |
Cross Section |
Ampacity (Air) |
Ampacity (Direct Burial) |
|
YJV / YJY (Cu) |
8.7/10kV |
3*95mm² |
240A |
215A |
|
YJV / YJY (Cu) |
8.7/10kV |
3*120mm² |
270A |
245A |
|
YJV / YJY (Cu) |
8.7/15kV |
3*150mm² |
305A |
275A |
|
YJV22 Armored |
26/35kV |
3*185mm² |
340A |
305A |
|
YJV22 Armored |
26/35kV |
3*240mm² |
390A |
350A |
Project: 500kW + 10kV Motor
Cable: 8.7/10kV YJV 3*120mm² Copper-clad Steel Cross-linked Polyethylene Cable
Current Carrying Capacity Design: More than 2.5 times the rated current
Result: Stable temperature, below 85°C, no overheating or aging.
Challenge: Dry sandy soil, high ground temperature
Solution: Upgrade to 3*150mm²; Derating factor 0.9
Result: Long-term safe operation, low failure rate.
Laying Method: Outdoor trench laying, multiple cables in parallel
Solution: YJY23 Armored UV-resistant Cable; Derating factor 0.85
Result: Stable operation under heavy load and harsh outdoor environment.
- Copper conductors should be used in high-reliability and high-current-carrying-capacity applications.
- Medium voltage cables must use cross-linked polyethylene (XLPE) insulation.
- Derating factors should be strictly applied in situations such as underground installation, group laying, high temperature, and poor ventilation.
- Impact loads should have a margin of 1.5 to 2.5 times the current carrying capacity.
- Armored cables (YJV22/YJY23) should be used for underground installations and in harsh environments.
- Monitor the temperature of joints and terminals to prevent overheating.
Current carrying capacity is fundamental to the safety and economy of medium-voltage cables. Based on IEC 60287 and IEEE field studies, conductor size, insulation thermal properties, laying method, and external thermal environment are the most critical factors. Appropriate selection, accurate calculation, and appropriate derating can effectively prevent overheating, insulation aging, and breakdown, thereby significantly extending service life and reducing total lifespan costs.
Jinhong Cable offers a full range of 6kV-35kV medium-voltage cross-linked polyethylene (XLPE) power cables, rigorously verified for current carrying capacity, and compliant with IEC, GB, CE, and RoHS standards, supporting global industrial, EPC, and infrastructure projects.
