The suite's IEC 60287 module with its default inputs: external thermal resistance T4, the rating equation in Ω/m, and how mutual heating changes T4 for a trefoil group.
| Conductor | θmax 90 °C, ground 30 °C, Rac = 0.161 Ω/km at 90 °C |
| Losses | Sheath loss factor λ1 = 0.10, armour λ2 = 0, dielectric loss neglected |
| Thermal resistances | T1 = 0.35, T2 = 0.03, T3 = 0.05 K·m/W (from the data sheet) |
| Installation | Buried at L = 1.0 m in soil of 1.2 K·m/W, cable diameter De = 95 mm |
R must be in Ω/m. Using Ω/km in this formula gives a rating about 32 times too high.
For three equally loaded single-core cables touching in trefoil, IEC 60287-2-1 gives T4 for the group, which already includes the heating of each cable by the other two. Use n = 1 for each single-core cable.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| T4, isolated cable | IEC 60287-2-1 §2.2.2 | 0.714 K·m/W | ✓ PASS |
| Rating, three-core cable | IEC 60287-1-1 eq. (1) | 354 A | ✓ PASS |
| T4, trefoil group | IEC 60287-2-1 §2.2.3 | 1.782 K·m/W | ✓ PASS |
Key insight: Ignoring mutual heating is the most common error in hand IEC 60287 calculations for single-core cables: the group's T4 is two to three times that of one isolated cable.
Every input in this example is editable in the live calculator — no signup needed.
Open Cable Engineering Suite (full workbench) calculator →From the cable's dimensions and material resistivities (IEC 60287-2-1 §2.1), or the manufacturer's data sheet. The suite's module takes them as inputs.
Use module H3 (Current Rating — Trench / Duct Bank), which adds the duct air space T4′ and duct wall T4″ and the mutual heating of several circuits.