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AC Cable Sizing

Inverter-to-panel AC cable size from voltage drop and current.

Electrical

Inputs (SI units)

Results

Recommended cable
2.5 mm² Copper
Design current
14.2 A
Minimum theoretical area
1.83 mm²
Actual voltage drop
6.07 V (1.46 %)
Cable power loss
0.149 kW
I²R loss at full load
Suggested breaker
20 A
≥ 1.25 × I per IEC 60364

Save & Load Project

Designs are stored privately in this browser — nothing is uploaded.

Engineering Formula

  • I = P / (V × pf) (1-φ)
  • I = P / (√3 × V × pf) (3-φ)
  • ρ_T = ρ₂₀ × [1 + α (T − 20)]
  • A = (2 × ρ_T × L × I) / ΔV (1-φ)
  • A = (√3 × ρ_T × L × I) / ΔV (3-φ)

AC current is derived from power, voltage and power factor, then the minimum conductor cross-section follows from the permitted voltage drop. Resistivity is corrected to the operating conductor temperature, and the result is rounded up to the next standard cross-section.

Step-by-step Calculation

  1. 1.Design currentP/(√3·V·pf)14.2 A
  2. 2.Resistivity at Tρ₂₀[1+α(T−20)]0.02058 Ω·mm²/m
  3. 3.Allowable dropV × vd%8.3 V
  4. 4.Required area√3·ρ·L·I/ΔV1.83 mm²
  5. 5.Rounded upnext standard size2.5 mm²

How to use this calculator: AC Cable Sizing

Inverter-to-panel AC cable size from voltage drop and current. The example below is calculated by this page's real engine from the displayed inputs.

  1. 1Confirm that the AC Cable Sizing matches the quantity or design check you need.
  2. 2Enter AC power, System voltage, and Power factor using the units printed beside each field.
  3. 3Select the applicable Phases and Conductor material options; these choices change the calculation method or factors.
  4. 4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
  5. 5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

InputExample valueWhy it matters
AC power10 kWMeasured or known ac power used by the calculation engine.
System voltage415 VMeasured or known system voltage used by the calculation engine.
PhasesThree phaseSelect the option that matches the real installation or scenario.
Power factor0.98 -Measured or known power factor used by the calculation engine.
One-way cable length30 mMeasured or known one-way cable length used by the calculation engine.
Allowable voltage drop2 %Measured or known allowable voltage drop used by the calculation engine.
Conductor materialCopperSelect the option that matches the real installation or scenario.
Conductor temperature70 °CMeasured or known conductor temperature used by the calculation engine.

Formula inputs & variables for AC Cable Sizing

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / inputUnitMeaning in this calculation
AC powerkWMeasured or known ac power used by the calculation engine.
System voltageVMeasured or known system voltage used by the calculation engine.
Phases—Select the option that matches the real installation or scenario.
Power factor-Measured or known power factor used by the calculation engine.
One-way cable lengthmMeasured or known one-way cable length used by the calculation engine.
Allowable voltage drop%Measured or known allowable voltage drop used by the calculation engine.
Conductor material—Select the option that matches the real installation or scenario.
Conductor temperature°CMeasured or known conductor temperature used by the calculation engine.

How the AC Cable Sizing works

The AC Cable Sizing uses AC power, System voltage, Phases, Power factor, One-way cable length, Allowable voltage drop, Conductor material, and Conductor temperature to calculate Recommended cable, Design current, Minimum theoretical area, Actual voltage drop, Cable power loss, and Suggested breaker. Its engine applies I = P / (V × pf) (1-φ); the worked values below come from that same live calculation rather than a separately typed example.

With AC power 10 kW, System voltage 415 V, Phases Three phase, Power factor 0.98 -, One-way cable length 30 m, Allowable voltage drop 2 %, Conductor material Copper, and Conductor temperature 70 °C, the main worked-example result is Recommended cable = 2.5 mm² Copper.

How each AC Cable Sizing input is used

AC power

The AC Cable Sizing worked example uses AC power = 10 kW. This value is passed directly into the calculation, with an allowed minimum 0.1.

System voltage

The AC Cable Sizing worked example uses System voltage = 415 V. This value is passed directly into the calculation, with an allowed minimum 100 and maximum 1000.

Phases

The AC Cable Sizing worked example selects “Three phase”. Available choices include Single phase and Three phase. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Power factor

The AC Cable Sizing worked example uses Power factor = 0.98 -. This value is passed directly into the calculation, with an allowed minimum 0.5 and maximum 1.

One-way cable length

The AC Cable Sizing worked example uses One-way cable length = 30 m. This value is passed directly into the calculation, with an allowed minimum 1.

Allowable voltage drop

The AC Cable Sizing worked example uses Allowable voltage drop = 2 %. This value is passed directly into the calculation, with an allowed minimum 0.5 and maximum 5.

Conductor material

The AC Cable Sizing worked example selects “Copper”. Available choices include Copper and Aluminium. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Conductor temperature

The AC Cable Sizing worked example uses Conductor temperature = 70 °C. This value is passed directly into the calculation, with an allowed minimum 20 and maximum 110.

AC Cable Sizing formulas and result interpretation

Formula 1: relationship used

In the AC Cable Sizing, I = P / (V × pf) (1-φ). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 2: relationship used

In the AC Cable Sizing, I = P / (√3 × V × pf) (3-φ). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 3: relationship used

In the AC Cable Sizing, ρ_T = ρ₂₀ × [1 + α (T − 20)]. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 4: relationship used

In the AC Cable Sizing, A = (2 × ρ_T × L × I) / ΔV (1-φ). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 5: relationship used

In the AC Cable Sizing, A = (√3 × ρ_T × L × I) / ΔV (3-φ). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Recommended cable

For the displayed AC Cable Sizing worked example, Recommended cable is 2.5 mm² Copper. Verify AC power, System voltage, and Phases and their units before relying on this output.

Design current

For the displayed AC Cable Sizing worked example, Design current is 14.2 A. Verify AC power, System voltage, and Phases and their units before relying on this output.

Minimum theoretical area

For the displayed AC Cable Sizing worked example, Minimum theoretical area is 1.83 mm². Verify AC power, System voltage, and Phases and their units before relying on this output.

Actual voltage drop

For the displayed AC Cable Sizing worked example, Actual voltage drop is 6.07 V (1.46 %). Verify AC power, System voltage, and Phases and their units before relying on this output.

Cable power loss

For the displayed AC Cable Sizing worked example, Cable power loss is 0.149 kW. I²R loss at full load Verify AC power, System voltage, and Phases and their units before relying on this output.

Suggested breaker

For the displayed AC Cable Sizing worked example, Suggested breaker is 20 A. ≥ 1.25 × I per IEC 60364 Verify AC power, System voltage, and Phases and their units before relying on this output.

AC Cable Sizing accuracy, checks and limitations

  • AC Cable Sizing units check: confirm AC power (kW), System voltage (V), Phases, Power factor (-), One-way cable length (m), Allowable voltage drop (%), Conductor material, and Conductor temperature (°C) before calculating.
  • AC Cable Sizing result check: compare Recommended cable, Design current, Minimum theoretical area, Actual voltage drop, Cable power loss, and Suggested breaker with the substituted formula steps and the displayed rounding precision.
  • AC Cable Sizing: Use this result for preliminary design and cross-checking. Confirm the applicable code edition, manufacturer data, site conditions and qualified-engineer approval before final design or installation.

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using AC Cable Sizing

  • Do not mix units for AC power (kW), System voltage (V), Power factor (-). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
  • Do not leave Phases on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
  • Do not replace the displayed I = P / (V × pf) (1-φ) relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
  • Do not treat Recommended cable = 2.5 mm² Copper from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the AC Cable Sizing is useful

AC Cable Sizing is designed for cases where AC power, System voltage, Phases, Power factor are known and you need Recommended cable, Design current, Minimum theoretical area. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is I = P / (V × pf) (1-φ). If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

AC power and System voltage: what changes the answer

The worked example uses AC power = 10 kW, System voltage = 415 V, Phases = Three phase, Power factor = 0.98 -. With those values, Recommended cable is 2.5 mm² Copper. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: AC power (kW): Measured or known ac power used by the calculation engine. System voltage (V): Measured or known system voltage used by the calculation engine. Phases: Select the option that matches the real installation or scenario. Available choices include Single phase, Three phase. Power factor (-): Measured or known power factor used by the calculation engine.

How to sanity-check a AC Cable Sizing result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Recommended cable, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with 100 & 200 Amp Service Wire Size Calculator

Useful next check because both tools use Conductor material, while 100 & 200 Amp Service Wire Size Calculator answers a different part of the same workflow.

Open 100 & 200 Amp Service Wire Size Calculator

Design Assumptions

  • • Balanced load, negligible reactance (short runs, ≤ 120 mm²).
  • • Voltage drop is the governing criterion; ampacity is checked separately.
  • • Standard PVC/XLPE insulated Cu/Al cable at the stated conductor temperature.

Engineering Tips

  • ◆IEC 60364-5-52 recommends ≤ 3% drop for final circuits, ≤ 5% total.
  • ◆Above 120 mm² include reactance — use manufacturer mV/A/m tables.
  • ◆Apply grouping and ambient derating factors before finalising the size.

Warnings

  • ▲Never size AC cable on voltage drop alone — verify ampacity and short-circuit withstand.
  • ▲Aluminium requires bi-metallic lugs and higher torque checks.

Standards & References

IEC 60364-5-52 (wiring systems)IS 732 (Code of practice)IEC 60228 (conductors)

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