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Single-Phase • Current • Amps

Calculate Current for Single-Phase

Calculate the current in amps from power, voltage and power factor cos φ.

Calculation Values

Note: This calculation is a technically sound simplification typical of online calculators. For practical sizing, standards, installation method, temperature, grouping, protective devices, cable type and manufacturer specifications must also be checked.

Formula Used

For single-phase systems:

I = P / (U × cos φ)

I is the current in amps, P the real power in watts, U the voltage in volts and cos φ the power factor.

FAQ

Frequently Asked Questions about Calculate Current for Single-Phase

Briefly explained: formula, use case and key limits of the calculation.

Which formula applies to single-phase? +

For single-phase systems, the technically correct formula is I = P / (U × cos φ), where P is the real power.

When may I use I = P / U? +

I = P / U applies to purely resistive loads or when cos φ = 1 is assumed.

What does cos φ mean? +

cos φ is the power factor. It describes the ratio of real power to apparent power.

Why does the current increase with a smaller cos φ? +

With a smaller power factor, a higher apparent power — and therefore a higher current — is needed for the same real power.

Practical guidance

Understand current drawn by a 230 V load

Single-phase current is active power divided by voltage and power factor. The method suits one steady load.

Input values explained

Power in watts
Use the electrical active power drawn by the load. A nameplate, data sheet or power meter is more reliable than an estimate.
Voltage
Enter the voltage between line and neutral. This is commonly 230 V in low-voltage systems.
Power factor cos φ
cos φ is the ratio of active to apparent power. It is close to 1 for resistive heating loads; use the data-sheet value for motors and transformers.

Example: 2,000 W heater

A mostly resistive heater takes 2,000 W at 230 V, so cos φ can be approximated as 1.

I = 2,000 W ÷ (230 V × 1) ≈ 8.70 A

Steady current is about 8.70 A. An electronic load of equal wattage can have a different current waveform and power factor.

Prefer the manufacturer's rated current

A nameplate current is normally more useful for actual design than a calculation from rounded power data.

Calculation limits

  • Cycling, inrush and nonsinusoidal current are excluded.
  • The result does not define cable size or breaker rating.