3-Phase Current: kW, kVA & Amps

Three-phase systems use line quantities and phase quantities. Line-to-line voltage is measured between two supply lines. Phase voltage is the voltage across one phase of the connected load. Line current is the current in a supply line, while phase current is the current through one load phase. The relationship between these quantities depends on whether the load is connected in Wye, also called Star, or Delta.

Real power is measured in kW and represents useful work. Apparent power is measured in kVA and combines voltage and current without treating all current as useful work. Power factor is the ratio of real power to apparent power. Fluke describes this relationship as PF = kW ÷ kVA, so a lower power factor requires more current for the same real power.

For a balanced three-phase load when real power is known, line current can be estimated with I = kW × 1000 ÷ (√3 × VLL × PF). VLL is line-to-line voltage. When apparent power is known, use I = kVA × 1000 ÷ (√3 × VLL). The square-root-of-three term is approximately 1.732 and represents the relationship between total three-phase power and line quantities.

For example, a balanced 150 kW load at 480 V line-to-line with a 0.90 power factor has an estimated line current of about 200.5 A. The same real power at a lower power factor would require more current because the apparent power is higher. This is why kW alone is not enough to choose conductors or equipment.

In a balanced Wye system, line current equals phase current and line-to-line voltage is √3 times phase voltage. In a balanced Delta system, phase voltage equals line-to-line voltage and line current is √3 times phase current. The 3-Phase Load Calculator asks for the load connection so it can show the relevant phase voltage and current relationships.

These relationships assume a balanced, steady-state model. A real facility may contain unequal single-phase loads, motor starting current, nonlinear loads, harmonics, different power factors, or a neutral conductor. Those conditions can change the current distribution and should be reviewed with measurements and equipment data when they matter.

When phase-by-phase real power is available, enter the values for phases A, B, and C instead of using only a total load. The calculator estimates each phase current, then reports the maximum, average, and percentage difference between the highest and lowest current. A large difference is a signal to review the load schedule and phase assignment.

The approximate neutral-current result is not a phasor measurement. Actual neutral current depends on current angles, harmonic content, connection details, and the power factor of each load. Treat the result as a planning indicator rather than a protection or conductor-sizing decision.

The calculated current is one input to a larger design. Conductor ampacity, continuous-load rules, voltage drop, overcurrent protection, transformer capacity, fault current, disconnect ratings, grounding, phase sequence, and local utility requirements can all affect the final selection. A three-phase current result does not approve a breaker, cable, generator, or transformer.

Use the Electrical Load Calculator for an initial dwelling load schedule, then use the three-phase tool when the system and load require line-current relationships. Have the final design reviewed by a qualified electrical professional before construction or energization.