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To truly understand the value of IEC 949, one must understand the difference between and non-adiabatic thermal assumptions. 1. The Adiabatic Assumption (IEC 60949 / IEC 60865)
Have you successfully used the non-adiabatic method from IEC 949 in a project? The calculations can be complex, but they save thousands of dollars in copper costs on large installations.
: IEC 60949 provides a "modifying factor" to account for heat escaping into adjacent materials, allowing for a more accurate (and often higher) permissible current rating. The Core Formula iec 949 pdf
While safe, the adiabatic method ignores reality. In a physical cable layout, some thermal energy immediately transfers to adjacent materials like insulation, bedding, or sheaths. by establishing a standardized, non-computerized mathematical framework to factor in this heat loss safely, resulting in more economical cable choices without risking thermal degradation. Key Formulas: Adiabatic vs. Non-Adiabatic
The thermal volumetric capacity of the surrounding insulation.
: Material constant (e.g., 226 for copper, 148 for aluminium). : Cross-sectional area of the conductor ( mm2m m squared θftheta sub f : Final permissible temperature ( ∘Craised to the composed with power cap C θitheta sub i : Initial temperature before the fault ( ∘Craised to the composed with power cap C Because IEC standards are protected by copyright, official,
The maximum limit the insulation can handle during a fault before degrading (e.g., 250°C for XLPE). Fault Duration (
) : Calculate a factor that accounts for heat dissipation into adjacent materials. : Multiply the adiabatic current by the modifying factor ( The Fundamental Adiabatic Formula
: For conductors with cross-sectional areas less than 10mm210 m m squared , the increase in permissible current can be significant. The Adiabatic Assumption (IEC 60949 / IEC 60865)
The standard (originally published as IEC 949) defines the methodology for calculating thermally permissible short-circuit currents for electrical cables and conductors . It is primarily used to ensure cable sizing can withstand the heat generated during a fault without damaging the insulation. Standard Overview
The standard follows a three-step procedure to determine the maximum current a cable can withstand without permanent damage: Calculate the Adiabatic Current ( IADcap I sub cap A cap D end-sub