Horsepower Calculator — AC Two Phase (4-Wire) Power Supply

This completes the single / two / three-phase horsepower set for a two-phase, 4-wire AC supply. It ties together horsepower, voltage, current, efficiency, and power factor: enter any four and it returns the fifth.

Why the factor is 2

A two-phase 4-wire system is really two separate single-phase circuits, 90° apart, each with its own pair of wires. Each phase delivers its own E · I · PF of real power, so the total is exactly twice a single phase: HP = 2 · E · I · EFF · PF / 745.7. That is the whole story of the phase factor — 1 for single phase, 2 for two-phase 4-wire, and √3 (≈ 1.732) for three phase. Use the per-phase voltage and per-phase current, and enter efficiency and power factor as decimals between 0 and 1.

Solve in any direction

• Current — the per-phase amps a known motor draws, for conductor and overload sizing.
• Horsepower — the shaft power implied by measured voltage and current.
• Efficiency or power factor — backed out from the other four; a solved value above 1.0 signals inconsistent inputs.

A note on two-phase systems

Two-phase power is largely historical — it survives in a few legacy installations but nearly all modern supplies are single- or three-phase. If you are not certain your supply is genuinely two-phase 4-wire, you probably want the single-phase or three-phase calculator instead.

Worked example

A 230 V (per phase) two-phase 4-wire motor drawing 10 A per phase at 0.85 efficiency and 0.85 power factor delivers HP = 2 · 230 · 10 · 0.85 · 0.85 / 745.7 ≈ 4.46 hp (3.32 kW) — exactly twice the single-phase result for the same figures. It draws 4600 VA of apparent power and 3910 W of real power, of which 3324 W reaches the shaft.