Mastering Ampacity Logic
ConduitLab automates the complex derating rules found in the NEC. Here is how the logic works conceptually, without needing to memorize the tables.
1. Temperature Correction
Conductors are rated for a specific maximum operating temperature (e.g., 60°C, 75°C, or 90°C). When the ambient temperature exceeds the baseline (typically 30°C), the conductor's ability to dissipate heat is reduced.
The NEC requires applying a correction factor less than 1.0 to reduce the allowable ampacity, ensuring the insulation does not melt/degrade. ConduitLab automatically selects the correct factor based on your input temperature.
2. Rooftop Adders
Conduits exposed to direct sunlight on rooftops experience extreme heat gain. The code requires adding a specific temperature value to the ambient temperature before calculating correction.
This "adder" varies based on how high the conduit is off the roof. ConduitLab handles this logic merely by asking for the height distance.
3. Bundling Adjustments
When more than three current-carrying conductors are bundled in a single raceway, they heat each other up. This mutual heating requires a further reduction in ampacity (an adjustment factor).
Our engine counts your CCCs and applies the appropriate percentage reduction automatically.
Automate these calculations today