Model soil, temperature, spacing, depth, and grouping impacts. Calculate adjusted current, resistance, and thermal margins. Build reliable underground cable ratings with clear practical outputs.
Use the form below to estimate buried cable ampacity with thermal and installation derating.
This calculator combines cable resistance, thermal resistance, and practical derating factors to estimate underground ampacity under steady-state conditions.
R20 = ρ20 / A
Rθ = R20 × [1 + α × (θmax − 20)] × Kskin
Ttotal = Tins + Tjacket + Tsoil
Tsoil = [ρsoil / (2π)] × ln(4L / D)
Ibase = √[(θmax − θsoil) / (Rθ × Ttotal)]
Iadjusted = Ibase × Fcores × Fgroup × Fbonding × Finstall × Fsafety
μ = 0.3LF + 0.7LF²
Annual losses = n × I² × Rθ × length × 8760 × μ / 1000
Where A is conductor area, ρ20 is resistivity at 20°C, α is the temperature coefficient, θmax is insulation temperature limit, and μ is the loss factor based on the daily load factor.
| Case | Material | Area (mm²) | Insulation | Soil Temp (°C) | ρ Soil (K·m/W) | Depth (m) | Group | Spacing (mm) | Estimated Ampacity (A) |
|---|---|---|---|---|---|---|---|---|---|
| Feeder A | Copper | 240 | XLPE | 25 | 1.2 | 0.80 | 1 | 100 | Approx. 520–540 |
| Feeder B | Aluminum | 185 | XLPE | 30 | 1.5 | 0.90 | 2 | 75 | Approx. 300–340 |
| Feeder C | Copper | 95 | PVC | 25 | 1.2 | 0.70 | 3 | 50 | Approx. 170–210 |
Ampacity is the continuous current a buried cable can carry without exceeding its permissible conductor temperature under the stated installation and soil conditions.
Soil thermal resistivity controls how easily heat leaves the cable. Higher resistivity traps heat, raises conductor temperature, and reduces allowable current.
Deeper burial increases the thermal path to the ground surface. That usually raises soil thermal resistance and reduces ampacity.
Grouped circuits warm each other through mutual heating. The calculator applies a grouping factor, while wider spacing can partially recover the lost ampacity.
Copper normally has lower electrical resistance than aluminum at the same area. Lower resistance reduces heating and usually allows higher current.
The extra safety margin intentionally derates the calculated current. It helps cover uncertainty, aging, future load growth, and site variation.
No. They are planning estimates based on selected design current, circuit length, and daily load factor. Real losses depend on actual load profile and temperature.
Use it for screening and early design. Final approval should still rely on project standards, manufacturer data, and detailed thermal studies when required.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.