Cable Rating And Derating Factor !new! May 2026

The 50mm² cable rated for 185A can only safely carry 60 Amps in these real conditions. It is entirely insufficient for a 150A load.

The NEC uses a formula based on conductor temperature rating. cable rating and derating factor

Trying a 240mm² cable (base rating ~ 450A): $450A \times 0.326 = 146.7A$ (Still slightly low). The 50mm² cable rated for 185A can only

– Number of current-carrying conductors in a raceway or cable: | Number of Conductors | Derating Factor | | :--- | :--- | | 1 – 3 | 1.00 | | 4 – 6 | 0.80 | | 7 – 9 | 0.70 | | 10 – 20 | 0.50 | | 21 – 30 | 0.45 | | > 30 | 0.40 | Trying a 240mm² cable (base rating ~ 450A): $450A \times 0

12 current-carrying conductors in bundle: $K_group = 0.50$ (NEC 10-20 conductors)

Note: Altitude affects air cooling but NOT buried cables. The Physics: Non-linear loads (VFDs, computers, rectifiers) generate harmonic currents. Triplen harmonics (3rd, 9th, 15th) add in the neutral conductor, causing overheating even if phase currents are balanced.