Electrical basics
Three-phase current calculator
Enter active power, line-to-line voltage and power factor to see the approximate line current, apparent power and reactive power. A first estimate for cables and protection, not a design calculation.
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P: active power, Q: reactive power, S: apparent power. The lower the cos φ, the longer the Q side. Not to scale.
How is it calculated?
For a balanced three-phase load, the line current follows from active power, line-to-line voltage and power factor. Apparent and reactive power come from the same triangle.
Line current
I = P × 1000 / (√3 × U_LL × cos φ)
P: active power (kW), U_LL: line-to-line voltage (V), cos φ: power factor, I: line current (A).
Apparent and reactive power
S = P / cos φ; Q = S × sin φ
S: apparent power (kVA), Q: reactive power (kVAr), sin φ = √(1 − cos² φ).
Example
- Inputs: P = 10 kW, U_LL = 400 V (example voltage; depends on your grid), cos φ = 0.9.
- Line current: 10 × 1000 / (√3 × 400 × 0.9) ≈ 16.0 A.
- Apparent power: 10 / 0.9 ≈ 11.1 kVA; reactive power ≈ 4.8 kVAr.
The example inputs are for illustration only; they are not verified defaults. Results are approximate and do not replace engineering advice.
Frequently asked questions
Why is there a √3 in the formula?
In a balanced three-phase system the line-to-line voltage is √3 times the line-to-neutral voltage. Total power is the sum of three phases, which leaves the √3 factor.
Which voltage should I enter?
Enter the line-to-line voltage. Low-voltage grids differ between countries (for example 400 V, 415 V or 480 V); use the nominal voltage of your own supply.
Can I size a cable from this current?
Not on its own. Cable sizing also depends on installation method, ambient temperature, grouping, voltage drop and short-circuit conditions. Treat this as a first estimate.
What happens when the power factor drops?
For the same active power, current and apparent power go up. The power factor correction calculator shows the capacitor power needed to reduce reactive power.