1Solve for

Ampacity: find the maximum continuous current this cable can carry. Check current: given a target current, find the resulting conductor temperature and voltage drop.

2Conductor & insulation

Cable productPick a real manufacturer product to use its own published current rating (and temperature correction, where published) instead of this tool's own physics calculation — or leave it on Generic to size a cable from first principles as before.

Conductor material

Size unit

Cross-section (IEC 60228 series)

InsulationISO 6722 sets insulation temperature classes for road-vehicle cables (A: 85°C up to H: 250°C). The insulation's rated temperature caps how hot the conductor is allowed to run — that limit, not a fixed current table, is what actually sets ampacity here.

XLPE (ISO 6722 Class D, 150°C)

Insulation wall thickness (mm)

3Operating conditions

Current type

DC for battery interconnects; AC for motor phase cables (uses skin effect at the drive's fundamental frequency).

Ambient / routing environment

Battery pack enclosure (~45°C)

Conductors in bundleCables run together in a harness/loom heat each other, reducing how much current each can carry compared to a single cable in free air. This uses the widely-published NEC 310.15(B)(3)(a) adjustment factors as a standard reference — modelling the actual mutual heating of N bundled round cables from first principles is a CFD-scale problem beyond this tool's scope.Derating factor: 1

Cable length, one-way (m)

Two-conductor circuit (voltage drop counts both supply and return conductors)Typical for EV HV circuits (battery/inverter/motor). Uncheck only for legacy chassis-return (e.g. 12V) wiring.

Results

Ampacity

166.4A

bundling factor 1

AC resistance

1.624mΩ/m

Conductor / outer diameter

4.514mm

outer 6.514 mm

Total thermal resistance

2.334K·m/W

Reference & assumptions

New to ISO 6722? Read the guide: EV Cable Sizing: What ISO 6722 Says About Ampacity — a plain-language explainer of the standard behind this calculator.

This tool is scoped to EV powertrain cabling (battery interconnects, battery-to-inverter, inverter-to-motor) — it does not use a household/building wiring ampacity table (e.g. NEC Table 310). Instead, ampacity/conductor temperature come from a first-principles steady-state heat balance: AC resistance (with the IEC 60287-1-1 skin-effect formula, reused from this site's Busbar calculator), conduction through the insulation wall, and natural convection + radiation from the round outer surface using the Churchill-Chu correlation for a horizontal cylinder (the correct correlation for round cable — flat-plate correlations, like the one used for busbars, don't apply here). The insulation's ISO 6722 temperature class sets the maximum allowable conductor temperature. ISO 6722's own numeric current-rating tables sit behind the paywalled standard text and weren't accessible during development — this tool computes from physics instead of transcribing an unverifiable table. Bundling derating reuses the widely-published NEC 310.15(B)(3)(a) adjustment factors as a disclosed standard reference, not a first-principles model of mutual heating between bundled cables. Treat this as a screening/estimation tool, not a substitute for the OEM harness qualification testing real cable assemblies undergo.

Named cable products (Premium) use each manufacturer's own published ampacity — real datasheet numbers, not this tool's physics — plus their own temperature-correction table where one is published. Data quality genuinely differs by manufacturer, disclosed rather than smoothed over: Glenair TurboFlex and Huber+Suhner RADOX publish real tabulated ampacity and correction curves, used directly; Champlain EXRAD publishes ampacity at a single 40°C baseline with no derating curve at all (shown as-is, not extrapolated); Coroplast/Coroflex publishes only simulated derating curves, not a tabulated number, so that preset instead feeds its real, sourced construction (bare copper, T180 silicone) into this tool's own physics model rather than presenting an imprecise chart-read as a datasheet figure. Every product's exact source datasheet is linked in the calculator.

Validated: the Churchill-Chu correlation was independently re-derived from the documented equation and matched the calculator's output exactly (80°C surface, 20°C ambient, 20 mm diameter → h = 8.058 W/m²K both ways) — comfortably inside the textbook-typical 2–25 W/m²K range for natural convection in air. The bundling-derating table matches the published NEC 310.15(B)(3)(a) factors exactly at spot checks (3 conductors → 1.00, 6 → 0.80, 30 → 0.45), and the AC resistance/skin-effect formula is the same one validated on the Busbar calculator.

Calculation steps

1. Conductor & outer diameter

d = √(4·A/π), D_outer = d + 2×insulation thickness

A = 16 mm², insulation = 1 mm

d = 4.514 mm, D_outer = 6.514 mm

2. AC resistance per metre (IEC 60287-1-1 skin-effect factor, reused from the Busbar calculator)

R_dc(T) = ρ20·(β+T)/(β+20) / A; xs² = 8πf/R_dc × 10⁻⁷; ys = xs⁴/(192+0.8xs⁴); R_ac = R_dc·(1+ys)

Copper, T = 150°C, DC (no skin effect)

R_ac = 1.6241 mΩ/m

3. Insulation conduction resistance per metre

R_ins = ln(D_outer/d) / (2π·k_insulation)

k = 0.33 W/m·K

R_ins = 0.1769 K·m/W

4. Natural convection from the cable surface (Churchill-Chu, horizontal cylinder)

Ra_D = g·β·ΔT·D³/ν² · Pr; Nu_D = {0.60 + 0.387·Ra_D^(1/6) / [1+(0.559/Pr)^(9/16)]^(8/27)}²; h = Nu_D·k_air/D

D_outer = 6.51 mm, ambient = 45°C

h_conv = 12.42 W/m²K (Ra_D = 9.67e+2, Nu_D = 2.59) + radiation, combined film resistance = 2.1567 K·m/W

5. Bundling derating (NEC 310.15(B)(3)(a)-style standard reference table)

1-3 conductors: 1.00 · 4-6: 0.80 · 7-9: 0.70 · 10-20: 0.50 · 21-30: 0.45 · 31-40: 0.40 · 41+: 0.35

1 current-carrying conductor(s) in the bundle/loom

Bundling factor = 1

6. Ampacity (steady-state heat balance)

I = √(ΔT_max / (R_ac · R_thermal)) × bundling factor, ΔT_max = insulation max temp − ambient, R_thermal = R_ins + R_film

ΔT_max = 150 − 45 = 105 K, R_thermal = 2.3336 K·m/W

Ampacity = 166.4 A

Cable/Wire Sizing Calculator (EV Powertrain)