Anyone working with three-phase power – on construction sites, in workshops or when planning industrial systems – needs the formula P = √3 × U × I × cos φ. Our calculator handles all the maths.
Three-Phase Power Basics
Three-phase alternating current is transmitted via three conductors with 120° phase shift each. In Europe, the line voltage is 400 V between phases and 230 V between phase and neutral.
Step by Step
- Select mode: Calculate power, current or voltage
- Enter known values: Voltage (V), current (A) or power (kW)
- Set cos φ: Default 0.85 for mixed loads
- Read results: Active power, apparent power, phase values and recommended breaker
Practical Example
A motor draws 16 A at 400 V with cos φ = 0.85: P = √3 × 400 × 16 × 0.85 = 9,418 W ≈ 9.4 kW.
- Why the √3 factor?
- Because the three phases are offset by 120°. The geometric addition of currents produces the factor √3 between phase and line quantities.
- When do I need three-phase power?
- Above approx. 3.7 kW (16A single-phase). Typical loads: oven, instantaneous water heater, EV wallbox, machine tools.
