Three-Phase Power Calculator

About the Three-Phase Power Calculator

Three-phase power is the standard for commercial, industrial, and large residential electrical systems worldwide. It uses three conductors carrying alternating currents that are 120 degrees out of phase, which produces steadier power delivery than single-phase service.

Three-phase systems deliver √3 (1.732) times more power than single-phase using only 1.5 times the conductors. Most commercial buildings, factories, large HVAC systems, machine tools, and EV fast chargers use three-phase service. Common voltages include 208V, 240V, 480V, and 600V in North America and 380V/400V in many other countries.

This page computes real power (kW), apparent power (kVA), and current for balanced three-phase systems. It is most useful when checking motor loads, sizing feeders and breakers, or verifying that measured current matches nameplate expectations.

When This Page Helps

Three-phase power calculations are fundamental for commercial and industrial electrical work. This page handles the √3 factor and power factor math so you can quickly move between kW, kVA, and amps when planning a circuit, checking a generator load, or reviewing motor and panel capacity.

How to Use the Inputs

1. Enter the line-to-line voltage (e.g., 480V, 208V).
2. Enter the line current in amps.
3. Enter the power factor (0.80–0.95 for typical motor loads).
4. View real power (kW), apparent power (kVA), and reactive power (kVAR).
5. Use results for panel sizing, breaker selection, and generator sizing.
6. Verify measurements against nameplate ratings.

Example Calculation

Tips & Best Practices

• Always use line-to-line voltage (not line-to-neutral) in the three-phase formula.
• Power factor for motors: 0.80–0.90 loaded, 0.30–0.50 unloaded.
• Use a clamp meter to measure actual line current on each phase for balance verification.
• Imbalanced loads can cause neutral current and should be investigated.
• VFDs (variable frequency drives) on motors can improve power factor to near unity.
• For delta connections, phase current = line current / √3.

Three-Phase Configurations

Wye (Star): Has a neutral conductor. Provides two voltages (e.g., 480V line-to-line and 277V line-to-neutral). Most common in commercial buildings. Delta: No neutral conductor. Provides one voltage (line-to-line). Common in industrial motor applications.

Power Triangle

Real power (kW), reactive power (kVAR), and apparent power (kVA) form a right triangle. kVA = √(kW² + kVAR²). Power factor = kW / kVA = cos(φ). Improving power factor reduces apparent power and current for the same real power output.

Common Three-Phase Applications

Large motors (5+ HP), commercial HVAC systems, industrial machinery, welding equipment, DC fast chargers for EVs, and data center power distribution all use three-phase power for efficiency and the ability to deliver high power through smaller conductors.

Frequently Asked Questions

• What is the √3 factor in three-phase power?

  The √3 (1.732) factor arises from the 120-degree phase angle between the three phases. It accounts for the vector sum of the three-phase currents. It applies when using line-to-line voltage in the power formula.

• What is the difference between kW and kVA?

  kW is real power (doing useful work). kVA is apparent power (total power drawn, including reactive component). kW = kVA × power factor. Generators and transformers are rated in kVA because they must supply the full apparent power.

• How do I find current from kW?

  I = kW × 1,000 / (√3 × V × PF). For example, a 30 kW load at 480V and 0.85 PF draws: 30,000 / (1.732 × 480 × 0.85) = 42.5 amps per phase.

• What voltages are standard for three-phase?

  In North America: 208V/120V (wye), 240V (delta), 480V/277V (wye), and 600V. Internationally: 380V, 400V, 415V, and 440V are common. The voltage depends on the transformer configuration and local standards.

• What is a balanced three-phase load?

  A balanced load draws equal current on all three phases. Motors are inherently balanced. When single-phase loads (lighting, outlets) are distributed across phases, the goal is to balance them as evenly as possible to minimize neutral current.

• When do I use single-phase vs three-phase calculations?

  Use single-phase for loads connected between one phase and neutral (120V or 277V outlets, small equipment). Use three-phase for loads connected across all three phases (motors, large HVAC, three-phase panels). The formulas are different.