3 Phase Current Calculator (from kW, kVA, or HP)
Calculate three-phase line current from real power, apparent power, or motor horsepower at any line-to-line voltage. The result includes the per phase (winding) current for delta and wye connected loads and the equivalent kVA.
This is calculated load current, not a breaker or conductor size. For motors, NEC 430.6(A)(1) requires the full load current from Table 430.250 (not the nameplate and not this formula) when sizing conductors and protection. Use the full load current calculator for the code table values.
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The 3 phase current formula, and why √3 is in it
Three-phase power is the sum of the power in each phase. With a balanced load, total apparent power is S = √3 × V_LL × I, so the line current is power divided by √3 times the line-to-line voltage. Which power you start from decides what else goes in the denominator:
- kW: I = (kW × 1000) ÷ (√3 × V × pf)
- kVA: I = (kVA × 1000) ÷ (√3 × V)
- HP: I = (HP × 746) ÷ (√3 × V × pf × eff)
The √3 (about 1.732) comes from the 120-degree spacing between phases. Each line-to-neutral voltage is V_LL ÷ √3, and the three phases together carry three times the single-phase power: 3 × (V_LL ÷ √3) × I = √3 × V_LL × I. For a motor, horsepower is shaft output, so it is converted to watts (746 W per HP) and then divided by efficiency to get the electrical input.
Line current vs phase current in delta and wye
Line current is what flows in each feeder conductor, and it is what this calculator returns. In a wye (star) connected load, each winding is in series with its line, so the phase current equals the line current. In a delta connected load, each winding sits between two lines and carries the line current divided by √3. The feeder sees the same line current either way; the difference matters when you size or test the windings themselves.
Worked examples
- 50 kW at 480 V, pf 0.85: (50 × 1000) ÷ (1.732 × 480 × 0.85) = 70.8 A per line. If the load is delta connected, each winding carries 70.8 ÷ 1.732 = 40.8 A. The equivalent apparent power is 58.8 kVA.
- 150 kVA at 208 V: (150 × 1000) ÷ (1.732 × 208) = 416.4 A per line. No power factor is needed because kVA is already apparent power.
- 25 HP at 460 V, pf 0.85, 90% efficiency: (25 × 746) ÷ (1.732 × 460 × 0.85 × 0.90) = 30.6 A per line, about 24.4 kVA of input. For comparison, NEC Table 430.250 lists 34 A for a 25 HP motor at 460 V, and that table value is what you use for conductor and protection sizing.
Note how the 150 kVA load at 208 V draws several times the current of the 50 kW load at 480 V. Current scales inversely with voltage, which is why larger loads are served at higher voltages to keep conductor sizes practical.
3 phase current: frequently asked questions
How do you calculate 3 phase current from kW?
I = (kW × 1000) / (√3 × V_LL × pf). Real power (kW) has to be divided by power factor to get back to apparent power before converting to current. A 50 kW load at 480 V and 0.85 power factor draws (50 × 1000) / (1.732 × 480 × 0.85) = 70.8 A per line.
How do you calculate 3 phase current from kVA?
I = (kVA × 1000) / (√3 × V_LL). No power factor is needed because kVA is already apparent power. A 150 kVA load at 208 V draws (150 × 1000) / (1.732 × 208) = 416.4 A per line.
What is the per phase current in a delta or wye connection?
In a wye (star) connection the current in each winding is the same as the line current. In a delta connection each winding sits between two lines, so the winding (phase) current is the line current divided by √3. A delta load drawing 70.8 A per line carries 70.8 / 1.732 = 40.8 A in each winding. The line current, which is what this calculator gives, is the same either way.
Why does my clamp meter reading differ from the calculated current?
The formula assumes a balanced load running at the power you entered. Real loads are rarely at nameplate rating, the three phases are rarely perfectly balanced, and nonlinear loads such as drives and LED drivers add harmonic current that a true-RMS meter will pick up. Actual power factor and voltage also drift from the values you assumed. Expect the field reading to differ by several percent or more.
Can I use this calculated current to size a breaker?
Not directly. Conductor and overcurrent protection sizing follow the NEC, which applies continuous load factors, temperature and fill adjustments, and standard device ratings. For motors, NEC 430.6(A)(1) requires the full load current from Table 430.250 rather than the nameplate or a calculated value. Use this number as a load estimate, then size from the code.
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