The standard provides a clear, standardized methodology to calculate the maximum current that a cable's metallic sheath, screen, or armor can safely handle during a short circuit without exceeding safe temperature limits. 📘 Overview of IEC 949
The required input data can be complex, as the calculation's results depend significantly on design details. The standard may require detailed information on the cable's geometry, such as the number and diameter of individual wires, the presence of fillers or gaps, materials in contact with the wires, and the presence of spirally applied tapes above the conductive components.
I=ϵ⋅IADcap I equals epsilon center dot cap I sub cap A cap D end-sub is a modifying factor (usually ≥1is greater than or equal to 1 ) that accounts for heat loss. Summary Answer iec 949 pdf
The following practical formulae derived from IEC 60949 are widely used for sizing cables under short-circuit conditions.
I=ε⋅IADcap I equals epsilon center dot cap I sub cap A cap D end-sub The standard provides distinct sub-formulas to calculate depending on the physical component configuration: Tubular metallic sheaths, tapes, and structural armor wires Critical Material Constants ( The standard provides a clear, standardized methodology to
IEC 60949 PDF: Calculation of Thermally Permissible Short-Circuit Currents
, which ensures electrical cables are sized correctly to prevent thermal damage during a fault. I=ϵ⋅IADcap I equals epsilon center dot cap I
While many traditional calculations assume that all heat generated during a fault remains within the conductor (an "adiabatic" assumption), IEC 60949 refines this by accounting for the fact that a portion of this heat actually dissipates into the surrounding materials. This more realistic "non-adiabatic" approach can provide engineers with a more accurate and often more economical design. As described in its methodology, the standard follows a three-step process:
: Often used in conjunction with IEC 60949 to determine the initial operating temperatures (ampacity) before a fault occurs.