): The final rated current is found by multiplying the adiabatic current by the non-adiabatic factor.

): A modifying factor is calculated to account for heat dissipation into surrounding layers. Final Permissible Current (

I=IAD⋅εcap I equals cap I sub cap A cap D end-sub center dot epsilon Where to Access IEC 60949 Documents

IEC 60949:1988 (including Amendment 1:2008) is the international standard for calculating . Unlike simpler methods that assume no heat escapes the conductor (adiabatic), IEC 60949 provides a way to account for non-adiabatic heating effects , where some heat is absorbed by surrounding materials like insulation or sheaths. Key Formulas and Calculation Methods

While full, official copies require purchase, you can find detailed summaries and partial previews at these locations: IEC 60949:1988

: Material-dependent temperature constant (e.g., 234.5 for Copper). Determine the Non-Adiabatic Factor (

IAD=K⋅St⋅ln(θf+βθi+β)cap I sub cap A cap D end-sub equals the fraction with numerator cap K center dot cap S and denominator the square root of t end-root end-fraction center dot the square root of l n open paren the fraction with numerator theta sub f plus beta and denominator theta sub i plus beta end-fraction close paren end-root : Cross-sectional area (mm²). : Duration of the short circuit (seconds).