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Current Carrying Capacity

Current Carrying Capacity Calculator

Calculate the continuous steady-state cable current rating using the IEC 60287 thermal and electrical loss model.

Standard calculation IEC 60287-1-1:2023 AC steady-state current rating and cable losses Thermal resistance inputs T1, T2, T3 and T4
FORMULA USED
I = sqrt{[Δθ - Wd(0.5T1 + n(T2+T3+T4))] / [R T1 + n Rc(1+λ1)T2 + n Rc(1+λ1+λ2)(T3+T4)]}
Δθ : Permissible conductor temperature rise50.000 K
n : Number of loaded conductors3
R : Conductor resistance0.000100000 Ω/m
Rc : Corrected conductor resistance0.000100000 Ω/m
Wd : Dielectric loss0.000000 W/m
λ1 : Sheath loss factor0.000000
λ2 : Armour loss factor0.000000
T1 : Insulation thermal resistance0.500000 K·m/W
T2 : Bedding thermal resistance0.200000 K·m/W
T3 : Serving thermal resistance0.100000 K·m/W
T4 : External thermal resistance1.000000 K·m/W
Automatic mode derives conductor resistance and supported T values from SQL material and geometry data.
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Rac/Rdc at operating temperature. Use 1.0 only when additional AC effects are negligible or already included.
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Select the current-rating equation to use.
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Maximum conductor temperature minus ambient/reference temperature.
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Technical Reference

IEC 60287 Calculation Basis

AC permissible current rating I = sqrt{[Δθ - Wd(0.5T1 + n(T2+T3+T4))] / [R T1 + n Rc(1+λ1)T2 + n Rc(1+λ1+λ2)(T3+T4)]} IEC 60287-1-1:2023, current rating equations
IEC 60287 steady state rating equation. The 2023 edition distinguishes R and Rc where applicable.
DC permissible current rating I = sqrt{Δθ / [R′T1 + nR′T2 + nR′(T3+T4)]} IEC 60287-1-1:2023, DC cables up to 5 kV
Simplified DC equation for direct voltages up to 5 kV. R′ is conductor DC resistance per unit length at maximum operating temperature.
Permissible temperature rise Δθ = θmax - θambient IEC 60287-1-1:2023
Temperature difference between maximum conductor operating temperature and ambient/reference environment.
Metallic loss factors λ1 = Ws/Wc ; λ2 = Wa/Wc IEC 60287-1-1:2023, calculation of losses
Sheath and armour losses are represented as ratios to conductor losses in the current rating equation.
Generic annular layer thermal resistance T = ρ/(2π) × ln(Dout/Din) IEC 60287-2-1:2023, 4.1.2.1 and 4.1.3
Used for concentric cylindrical insulation, bedding and serving layers. For single-core conductor-to-sheath T1, CLL may be applied where relevant.
Single-core T1 T1 = ρ1/(2π) × ln(1 + 2t1/dc) / CLL IEC 60287-2-1:2023, 4.1.2.1
Single-core conductor-to-sheath thermal resistance.
Single isolated buried cable T4 T4 = ρe/(2π) × ln(u + √(u²−1)), u = 2L/De IEC 60287-2-1:2023, 4.2.2
External thermal resistance for the supported single isolated direct-buried geometry.
Conductor DC resistance at operating temperature Rθ = R20 × [1 + α20(θ−20)] IEC 60287 electrical-loss calculation basis
Temperature correction used before optional AC resistance correction factor.
Conductor resistance from material resistivity and area R20 = ρ20/A Engineering relation used as IEC 60287 input
A in m². Allows resistance to be derived from conductor material and actual cross-section.
References

Standards Used

IEC 60287-1-1:2023 Current rating equations at 100% load factor and calculation of losses. Edition 3.0, published 2023-05-22. https://webstore.iec.ch/en/publication/68118
IEC 60287-2-1:2023 Calculation of thermal resistance for steady-state cable current rating. https://webstore.iec.ch/en/publication/68134
IEC 60287-3-1:2017 Site reference operating conditions. National requirements can supersede general reference values. https://webstore.iec.ch/en/publication/33164