When cables are installed close together (e.g., in a tray, conduit, or duct bank), they radiate heat onto each other. This mutual heating prevents individual cables from cooling efficiently. The more cables in the group, the lower the grouping factor.
Running a 90°C XLPE cable through a 70°C boiler room reduces its capacity by 42%. A 100A cable becomes a 58A cable. cable rating and derating factor
Disclaimer: This guide is for educational purposes. Always consult licensed electrical engineers and local electrical codes (NEC, CEC, IEC, BS 7671) for final design decisions. When cables are installed close together (e
Let’s assume we need to size a cable with a standard rating of . Running a 90°C XLPE cable through a 70°C
If your real-world environment deviates from these,
Cable rating, also known as ampacity, is the maximum amount of electric current that a cable can carry without exceeding its temperature limit. The cable rating is determined by the cable's design, materials, and construction. The main factors that influence cable rating are:
Larger cables (often required after derating) help minimize voltage drop over long distances. Summary Checklist for Engineers To accurately rate a cable, always identify: