Glossary Derating
A companion glossary entry to the dedicated derating deep-dive, framed as a quick-reference definition.
Derating gets a full deep-dive elsewhere in this series ("What 'Derating' Actually Means"). Here's the quick-reference glossary version for when a fast explanation is all that's needed.
Derating is the process of reducing a cable's table-listed maximum ampacity to reflect real installation conditions that differ from the table's standard reference assumptions — most commonly, higher-than-reference ambient temperature and the presence of other current-carrying conductors sharing the same enclosed space.
Real usable ampacity = Table ampacity × Temperature correction factor × Grouping correction factor
Skipping derating means trusting a capacity figure the cable doesn't actually have — the difference between a table's headline number and a properly derated real-world figure can be substantial in a hot, crowded installation, which is exactly the scenario where undersizing has real consequences.
See the full explanation and worked examples in the "What 'Derating' Actually Means" article, or apply it directly in any OhmWorks Cable Sizing calculator.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks