HVC Cable Sizing Calculator
Pick a Fellten HVC cable size from your run length and your motor's real current profile: a high peak for a short time and a lower continuous current. The calculator compares every HVC size side by side for voltage drop, power loss and estimated conductor temperature, using the figures in our own cable datasheets.
For EV converters and installers sizing pack to inverter and inverter to motor runs.
Calculator
Enter your circuit. Results update as you type.
| Size | Status | Continuous temp | End of peak temp | Time to 125 °C at peak | Voltage drop at peak | Loss at continuous | Loss at peak | Shop |
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Estimates for guidance only. Final cable selection is the installer's responsibility and must follow the relevant regulations and the component manufacturers' ratings.
Conductor temperature through the peak
How it works
Each cable size is treated as one metre of copper conductor in XLPE insulation, under a PVC (vinyl) outer sheath. Current through the copper's resistance makes heat. The heat flows out through the XLPE and then the PVC to the cable surface, then into the surrounding air. Copper resistance rises as it warms, so a hotter cable makes more heat for the same current.
First the calculator finds the temperature the cable settles at on your continuous current. If heating keeps outrunning cooling, the size is marked thermal runaway and is not suitable. From that settled temperature it then applies the peak current for your peak duration, step by step, letting the copper, XLPE and PVC soak up heat while the surface keeps cooling. That gives the end of peak temperature, and how long the peak could last before the conductor reaches 125 °C.
Voltage drop and power loss use the resistance at the calculated temperature. A DC pair counts both conductors. A 3-phase run uses the line voltage drop and counts three conductors.
Show the formulas
- Resistance at temperature, per metre
R(T) = R20 × (1 + α × (T - 20)) - Thermal resistance, conductor to ambient (XLPE insulation out to the braid, PVC sheath outside it, braid ignored)
D_sh = D_out - 2 × sheath wall R_ins = (ρ_xlpe / 2π) × ln(D_sh / d_cond) R_sh = (ρ_pvc / 2π) × ln(D_out / D_sh) R_ext = 1 / (π × D_out × h × installation factor) R_th = R_ins + R_sh + R_ext (K·m/W) - Heat capacity per metre, using the actual copper area
A_cu = strands × π × (0.21 / 2)² A_ins = π/4 × (D_sh² - d_cond²) A_sh = π/4 × (D_out² - D_sh²) C = A_cu × 8960 × 385 + A_ins × 1400 × 1500 + A_sh × 1400 × 1200 (J/K·m) - Steady state at continuous current, by fixed-point iteration (up to 200 steps, stop below 0.01 K change; runaway if no convergence or above 250 °C)
T = T_amb + I_cont² × R(T) × R_th - Peak, integrated from the steady state in 0.05 s steps
dT/dt = (I_peak² × R(T) - (T - T_amb) / R_th) / C - Time to limit: the same integration continued until T reaches 125 °C, capped at 1 hour.
- Adiabatic check, worst case with no cooling at all
ΔT_adiabatic = I_peak² × R(T_ss) × t_peak / (A_cu × 8960 × 385) - Voltage drop
DC pair: V = I × R(T) × 2 × L 3-phase AC: V_line = √3 × I × R(T) × L - Power loss for the circuit
DC pair: P = I² × R(T) × 2 × L 3-phase AC: P = I² × R(T) × 3 × L
Assumptions and limits
The values the model uses. They are fixed in the page so every result is reproducible.
| Assumption | Value |
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- Temperatures are estimates from a simple thermal model and published resistance and dimensions. They are not a manufacturer current rating.
- The datasheets give no current rating or short-time overload limit, so the 125 °C operating limit is used for both continuous and peak. Good needs a margin below it: 90 °C continuous, the usual continuous rating for XLPE, and 115 °C at the end of a peak.
- The XLPE and PVC thermal values are typical published figures for those compounds. The supplier does not publish them.
- At these temperatures the cable surface gets hot. Keep it clear of anything that cannot take the heat, and check the connectors and lugs are rated for the conductor temperature.
- Real temperatures depend on routing, bundling, nearby heat sources and airflow. Use the installation setting and a realistic ambient.
- The cable is marked 700 V DC, with a nominal maximum of 1000 V DC. The calculator shows a warning if pack voltage is above 700 V.
- 3-phase voltage drop is resistive only. Cable reactance and skin effect are ignored, which is reasonable for short runs at motor frequencies.
- Each conductor is modelled on its own. In a DC pair or 3-phase run, cables laid together warm each other: use the bundled setting if they touch.
- Check connector and lug ratings too. The cable is rarely the only limit.
Cable data
Values from the HVC XLPE-125 technical datasheets. Diameters and wall thicknesses are the published maximum or minimum figures.
| SKU | Size | Strands | Conductor Ø | Core Ø | Insulation | Sheath | Outer Ø | R at 20 °C | Weight | Shop |
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