Running a 90°C XLPE cable through a 70°C boiler room reduces its capacity by 42%. A 100A cable becomes a 58A cable. 2. Grouping / Bundling Derating ($K_group$) The Physics: When cables are tied together in a tray, conduit, or bundle, they heat each other. The inner cables cannot radiate heat outward.
Introduction In the world of electrical engineering, the humble cable is often overlooked. Yet, it is the circulatory system of any electrical installation—from a small residential complex to a massive industrial plant. Selecting the wrong cable doesn't just lead to inefficiency; it leads to catastrophic failure, fire hazards, and prolonged downtime. cable rating and derating factor
12 current-carrying conductors in bundle: $K_group = 0.50$ (NEC 10-20 conductors) Running a 90°C XLPE cable through a 70°C
Correction factors for buried cables: | Soil Resistivity (K·m/W) | Correction Factor | | :--- | :--- | | 0.7 (Wet, marsh) | 1.05 – 1.10 | | 1.0 (Moist loam) | 1.00 | | 1.5 (Dry sand) | 0.85 | | 2.0 (Very dry gravel) | 0.70 | | 3.0 (Thermal backfill required) | 0.50 | Grouping / Bundling Derating ($K_group$) The Physics: When