Cable Sizing

Cross-section of low-voltage cables from current-carrying capacity, voltage drop and automatic disconnection. Current-carrying capacity from a thermal model per IEC 60287, with your own values if required

Sample values, replace with your own circuit data

Utilisation by cross-section

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Current-carrying capacity Voltage drop Disconnection Selected cross-section Conductor temperature Maximum operating temperature

Load & circuit System Voltage V, line-to-line / 1~ to N Frequency Hz Load Load given as Power factor cos φ Length m, one way Parallel cables per phase Third harmonic % of phase current

Cable & installation Conductor Insulation Installation method Cross-section Air temperature °C Ground temperature °C Soil thermal resistivity K·m/W Laying depth m

Grouping & limits Circuits in the group incl. this one Grouping factor empty = calculated Arrangement Max. voltage drop % Protective conductor

Protection & disconnection Protective device Rated current In A, empty = next size Disconnection time Tripping current Ia A, empty = typical Loop impedance at origin Ω, Zs upstream

Current-carrying capacity

Voltage drop

Disconnection & fault

Assessment

Cross-sections compared

Cross-section	Iz,eff A	Utilisation	θ conductor °C	ΔU %	Zs Ω	Zs,max Ω	Max. length ΔU m	Max. length Zs m	Result

Current-carrying capacity: model and own values

Reference conditions

Cross-section	T1 K·m/W	T3 K·m/W	T4 K·m/W	Cable Ø mm	IEC 60287 A	Own value A	Used A

Method: current-carrying capacity from the steady-state heat balance of IEC 60287-1-1 (Δθ = I²·R·[T1 + n·(T2 + T3 + T4)]) with AC resistance at maximum conductor temperature (skin and proximity effect), thermal resistances of insulation and sheath from typical dimensions per IEC 60502-1, and external thermal resistance per IEC 60287-2-1: free air with the convection constants of Table 2 and iteration of the surface temperature, ground with ρ and laying depth, conduit and duct with the air gap formula. Installation methods A to E are adjusted to the test arrangements of IEC 60364-5-52 Annex A; deviation from the tabulated values of IEC 60364-5-52 is typically within ±5 %, never more than 5 % higher. Reference conditions 30 °C air, 20 °C ground at 2.5 K·m/W, 0.7 m depth. Ambient, soil and depth are calculated directly with the model; grouping factors are approximations of IEC 60364-5-52 Tables B.52.17 to B.52.19; third harmonic per Annex E. Protection against overload per VDE 0100-430: Ib ≤ In ≤ Iz and I2 ≤ 1.45 × Iz (I2 = 1.45 In for MCB, 1.6 In for gG from 16 A, 1.3 Ir for circuit breakers). Voltage drop ΔU = k × Ib × L × (R′ cos φ + X′ sin φ) with k = √3 (three-phase) or 2 (single-phase) and R′ at the conductor temperature reached at Ib. Disconnection per VDE 0100-410 (TN system): Zs ≤ 0.95 × U0 / Ia with conductor resistance at maximum operating temperature (CLC/TR 50480); Ia = 5 / 10 / 20 × In for MCB B / C / D, typical values from gG time-current curves. Protective conductor per VDE 0100-540, adiabatic check S ≥ √(Ia² × t) / k with t = 0.1 s for MCBs and circuit breakers (instantaneous tripping) or the disconnection time for gG fuses. Disclaimer: this tool is a planning aid. Results are not a substitute for design by a qualified electrical engineer and must be checked against the applicable standards (DIN VDE 0298-4, DIN VDE 0100-410, -430, -520, -540) and the manufacturer data of cables and protective devices before installation. oxinon.com accepts no liability for damage resulting from the use of these results.

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