Code Comparison Derating
Each code’s ampacity tables assume a different baseline ambient temperature — a detail easy to overlook when comparing results.
A detail that trips up engineers moving between codes: the reference ambient temperature baked into each code's base ampacity tables isn't necessarily the same number, and treating "30°C" as a universal constant across all three is a mistake worth avoiding.
If a table's base ampacity assumes a lower reference temperature than another code's table, a like-for-like comparison of "base ampacity" numbers between the two codes is misleading without accounting for that different starting assumption — the derating correction each code applies afterward is calibrated to its own specific reference point.
Always confirm the specific reference ambient temperature for whichever table you're actually reading, rather than assuming it matches a number you remember from a different code. This is exactly the kind of detail that's easy to get right within one code and then carry incorrectly into another.
OhmWorks applies each code's own correctly-referenced correction automatically — no manual cross-code temperature adjustment needed as long as you're using the matching code's calculator tab.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks