( k_temp \times k_group \times k_depth \times k_soil \times k_altitude \times \dots ) 3.1 Ambient Temperature ((k_temp)) Higher ambient temperature reduces heat dissipation.
| Conductor Insulation | 30°C (Base) | 35°C | 40°C | 45°C | 50°C | |----------------------|-------------|------|------|------|------| | 70°C (PVC) | 1.00 | 0.94 | 0.87 | 0.79 | 0.71 | | 90°C (XLPE/EPR) | 1.00 | 0.96 | 0.91 | 0.87 | 0.82 |
| Soil Type | Thermal Resistivity | Derating Factor (vs 1.2 baseline) | |-----------|--------------------|------------------------------------| | Wet clay/loam | 0.8–1.0 | 1.05–1.10 | | Normal soil (baseline) | 1.2 | 1.00 | | Dry sand/gravel | 2.0–2.5 | 0.70–0.85 | | Concrete backfill | 1.0 | 1.00 | Deeper burial reduces cooling due to higher soil thermal resistance. cable derating factor
| Depth | Factor (up to 10kV) | |-------|---------------------| | 0.5 m | 1.00 | | 0.8 m | 0.96 | | 1.0 m | 0.94 | | 1.5 m | 0.90 | Reduced air density lowers convection cooling.
| Number of circuits/cables | Spacing (touching) | Spacing (≥1 cable diameter) | |---------------------------|--------------------|-----------------------------| | 1 | 1.00 | 1.00 | | 2 | 0.80 | 0.85 | | 3 | 0.70 | 0.80 | | 4-5 | 0.60 | 0.75 | | 6-8 | 0.50 | 0.70 | Standard soil is 1.2 K·m/W (e.g., damp clay). Dry sand or backfill can be >2.5 K·m/W. ( k_temp \times k_group \times k_depth \times k_soil
(I_derated = 210A \times 0.35 = 73.5A)
For a given installation, calculate the total derating factor before selecting conductor cross-section. This report is for informational purposes. Always follow local electrical codes and standards. | Number of circuits/cables | Spacing (touching) |
Note: For high temperatures >55°C, special cables are required. When multiple cables run together, each heats its neighbors.