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AC Cable Voltage Drop (R + X)

Estimate AC voltage drop using resistance, reactance, power factor, current and route length.

Updated September 2026

How it works

Estimate AC voltage drop using resistance, reactance, power factor, current and route length.

Formula:
ΔV1φ = 2·I·L·(R cosφ + X sinφ); ΔV3φ = √3·I·L·(R cosφ + X sinφ), L in km.

Before you use the result: Use R and X values appropriate to cable type, temperature and installation.

Practical use

Use verified material data and project geometry. Treat results as planning estimates and compare them with the energy/thermal requirements that apply to the project.

Keep units consistent with the source information.
Use project-specific densities, pack sizes and coverage rates where provided.
Round purchasing quantities to supplier packaging and delivery rules.

How to use this calculator: AC Cable Voltage Drop (R + X)

Estimate AC voltage drop using resistance, reactance, power factor, current and route length.

Quick workflow

Enter the project values from the latest drawing, specification or verified site measurement.
Check units, material properties, allowances and any code- or supplier-specific parameters before calculating.
Review the result together with the formula, assumptions and the related checks shown on this page.

Worked example

Example inputs: System: Three phase; Nominal voltage [V]: 400; Current [A]: 40; One-way route length [m]: 50.

Using the sample values built into the calculator, the calculation gives approximately: AC voltage drop: 2.387 V; AC voltage drop percent: 0.597%.

What the result means

Calculation method: ΔV1φ = 2·I·L·(R cosφ + X sinφ); ΔV3φ = √3·I·L·(R cosφ + X sinφ), L in km.

Before using the result: Use R and X values appropriate to cable type, temperature and installation.

Common questions

What does this calculator do?

Estimate AC voltage drop using resistance, reactance, power factor, current and route length.

Which inputs should I verify?

Key inputs to verify include: System, Nominal voltage [V], Current [A], One-way route length [m].

Can I use this result for final design or ordering?

Use the result as a transparent planning or checking aid. Final design, code compliance, supplier selection and project-specific decisions still need to be verified where applicable. Use R and X values appropriate to cable type, temperature and installation.

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