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Short Circuit

Adiabatic short circuit withstand calculations for conductors.

Primary StandardIEC 60949:1988 + AMD1:2008Thermally permissible short-circuit currentTemperature limits: IEC 60724 / IEC 60986 / IEC 61443
ScopeThis calculator determines cable thermal short-circuit withstand from IEC 60949. The prospective fault current itself should come from the electrical system short-circuit study, for example IEC 60909-0:2026 for applicable three-phase AC systems.
FORMULAS USED

IEC 60949 Short-Circuit Formulas

The equations below are the formulas used by this calculator. Formula text and visibility are SQL managed.

Quick k Factor MethodIsc = k × S / √tRequired area: S = Isc × √t / k. Rating conversion: I₂ = I₁ × √(t₁/t₂).
Permissible Short-Circuit Current · IEC 60949 Clause 2 I = ε × IAD I is the permissible RMS short-circuit current. ε is the non-adiabatic heat-loss factor. For an adiabatic calculation ε = 1.
Adiabatic Short-Circuit Current · IEC 60949 Clause 3 IAD² × t = K² × S² × ln[(θf + β)/(θi + β)] Equivalent form: IAD = (K × S / √t) × √ln[(θf + β)/(θi + β)].
Material Constant K · IEC 60949 Clause 3 and Table I K = √[σc × (β + 20) × 10⁻¹² / ρ20] K depends on the current-carrying material.
Final Short-Circuit Temperature · IEC 60949 Clause 4 θf = (θi + β) × exp[(IAD² × t)/(K² × S²)] − β For known Isc, first use IAD = Isc / ε.
Non-Adiabatic Factor, Conductor / Spaced Wires · IEC 60949 Clause 5.1 ε = √[1 + F × A × √(t/S) + F² × B × (t/S)] General IEC 60949 non-adiabatic expression for conductors and spaced wire screens.
Empirical Constant A · IEC 60949 Clause 5.1 A = (C1 / σc) × √(σi / ρi) C1 = 2464 mm/m.
Empirical Constant B · IEC 60949 Clause 5.1 B = (C2 / σc) × (σi / ρi) C2 = 1.22 K·m·mm²/J.
Non-Adiabatic Factor, Sheath / Screen / Armour · IEC 60949 Clause 6.1 ε = 1 + 0.61(M√t) − 0.069(M√t)² + 0.0043(M√t)³ IEC 60949 expression for sheaths, screens and armour.
Thermal Contact Factor M · IEC 60949 Clause 6.1 M = F × [√(σ2/ρ2) + √(σ3/ρ3)] / [2 × σ1 × δ × 10⁻³] δ is metallic thickness in mm.
Tubular Sheath Area · IEC 60949 Clause 6.2 S = π × d × δ d is mean sheath diameter.
Longitudinal Tape Area · IEC 60949 Clause 6.3.1 S = w × δ For overlap not exceeding 10% of tape width.
Helically Lapped Tape Area · IEC 60949 Clause 6.3.2 S = n × w × δ Total tape cross-sectional area.
Spaced Wire Screen Total Current · IEC 60949 Clause 5.3 Itotal = n × Iwire Calculate one isolated wire, then multiply by number of wires.
Use A√s/mm².
Profile provides IEC temperature-limit reference. Initial and final temperatures remain visible and editable.
mm²
s
°C
°C
kA
Use the RMS short-circuit current applicable over the entered duration.
IEC 60949 recommends 0.7 for conductor/wires. Clause 6 permits 0.9 when a metallic component is completely bonded on one side.
mm²
IEC 60949 Clause 5.3 calculates each isolated wire and multiplies by the number of wires.
mm
kA
s
s
I₂ = I₁ × √(t₁/t₂)
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Standard References

IEC 60949:1988 + AMD1:2008

Calculation of thermally permissible short-circuit currents. The standard calculates an adiabatic current, a non-adiabatic modifying factor, and the resulting permissible current.

IEC 60724:2000 + AMD1:2008

Short-circuit temperature limits for cables rated 1 kV and 3 kV. The stated temperature limits apply to short-circuits up to 5 s.

IEC 60986:2000 + AMD1:2008

Short-circuit temperature limits for cables rated from 6 kV up to 30 kV.

IEC 61443:1999 + AMD1:2008

Short-circuit temperature limits for electric cables above 30 kV. Permissible current in cable current-carrying components is calculated according to IEC 60949.

IEC 60909-0:2026

System short-circuit current calculation standard for low-voltage and high-voltage three-phase AC systems at 50 Hz or 60 Hz. Use it to determine the prospective fault current supplied to this cable-withstand calculator.

Calculator Scope

This module verifies thermal short-circuit withstand of a cable current-carrying component. It does not replace a full network short-circuit study, protection coordination study, or electrodynamic force calculation.