Introduction
The 3 Phase Current Calculator finds the line current in a three-phase electrical system. Enter your voltage, power, and power factor, and it returns the current in amps.
Three-phase power is used widely in industry.2 Larger motors usually need it.1 To pick the right wire size, breaker, or fuse, you need to know the current. Working it out by hand takes time and is easy to get wrong. The calculator runs the same arithmetic every time, so a slipped decimal does not end up in your wire sizing.
It uses the standard formula: I = P ÷ (√3 × V × PF).1 You can enter voltage as line-to-line or line-to-neutral, and pick units like volts, kilovolts, watts, kilowatts, or horsepower. The results show line current, apparent power (kVA), reactive power (kVAR), power per phase, and the phase angle.
You also get a full step-by-step solution, a table of results, and two charts. One chart shows how current changes with power factor. The other shows the power triangle. Electricians, engineers, and students can follow the worked steps to check their own figures before planning a job.
How to use our 3 Phase Current Calculator
Enter your supply voltage, the load power, and the power factor. The calculator gives you the line current in amps, plus apparent power (kVA), reactive power (kVAR), power per phase, the phase angle, and a full step-by-step solution.
Voltage: Type the supply voltage of your three phase system, like 400 or 480. Then pick the unit next to the box: V, kV, or mV.
Voltage Input Type: Choose Line-to-Line (L-L) if your voltage is measured between two phases. Choose Line-to-Neutral (L-N) if it is measured from one phase to neutral. The tool changes L-N to L-L for you by multiplying by √3.
Power (Real Power, P): Type the real power of the load and pick the unit: W, kW, MW, or HP. Use HP for motors rated in horsepower, and the tool turns it into watts.
Power Factor (PF): Enter a number from 0.01 to 1.00. Use 1.00 for pure resistive loads like heaters.5 A typical induction motor runs at around 85% power factor, so about 0.85 suits most motors.2 Check the motor nameplate if you have it.
Load Type: Pick Lagging for inductive loads such as motors and transformers. Pick Leading for capacitive loads. This only sets the plus or minus sign shown for reactive power Q.
Current Output Unit & Precision: Choose how to show the answer: A, kA, or mA. Then choose how many decimal places you want, from 0 to 4.
Press Calculate to see your results, the data table, the charts, and the worked steps. Press Reset to go back to the sample values, or Print Results to save a copy.
What Is Three-Phase Current?
Three-phase power uses three live wires instead of one.1 Each wire carries an equal voltage, and the three waves are spaced 120°, or one-third of a cycle, apart.3 Because the waves take turns peaking, the total power flowing into the load stays constant, in a smooth, steady stream.1 That is why larger motors use three-phase power instead of single-phase power.1
Three-phase current is the amount of electricity, measured in amps (A), that flows through each line wire of that system. Knowing this number matters because wires, breakers, fuses, and contactors are all picked by amps. Guess too low and the wire overheats. Guess too high and you pay for copper you do not need.
The Formula
For a balanced three-phase load, line current is found with:
I = P ÷ (√3 × VLL × PF)1
- I is the line current in amps
- P is the real power in watts (1 kW = 1,000 W; 1 HP ≈ 0.7457 kW)1
- √3 is about 1.732, the three-phase constant
- VLL is the line-to-line voltage in volts
- PF is the power factor, a number from 0.01 to 1.00
Line Voltage vs. Phase Voltage
Line-to-line (L-L) voltage is measured between any two hot wires.1 Line-to-neutral (L-N) voltage is measured from one hot wire to neutral.1 Line-to-line readings are 1.73 times line-to-neutral readings, so VLL = VLN × √3.1 That means a 400 V L-L system has about 230 V L-N, and a 208 V system has about 120 V. Always check which one you are reading before you plug it into the formula.
Why Power Factor Matters
Power factor tells you what part of the power the wires carry actually does useful work.3 Motors pull extra current to build the magnetic field in their windings, so their power factor is below 1.1 A load at 0.85 PF draws about 18% more current than the same load at 1.00 PF. Lower power factor means more amps for the same work, and that extra current wastes energy as heat in the wiring.2 A typical induction motor runs at around 85% power factor, so 0.85 is a common starting guess.2
Real, Reactive, and Apparent Power
Three kinds of power show up in AC systems:
- Real power (P) in watts is the part that does work, like turning a shaft or making heat.3
- Reactive power (Q) in VAR is the part that swings back and forth and does no work.3
- Apparent power (S) in VA is the total the wires must carry, found by S = √3 × VLL × I.3
Together they form a right triangle, the power triangle, where S² = P² + Q².4 Power factor is the ratio of real power to apparent power: PF = P ÷ S.3 In an inductive load, the current lags the voltage, so its power factor is called lagging.3 In a capacitive load the current leads, so its power factor is leading.3 Capacitors can supply some of a motor's reactive power, which raises the power factor.1
Wye and Delta Loads
In a wye (star) connection, phase current equals line current.3 In a delta connection, each phase winding carries line current divided by √3.3 Total power is the same either way, but the current inside the windings is not, so check the wiring before sizing anything internal.3
A Quick Example
A 50 kW load on 400 V three-phase at 0.85 power factor:
I = 50,000 ÷ (1.732 × 400 × 0.85) = 50,000 ÷ 588.9 = 84.91 A
That load needs a breaker and wire rated above 84.91 A, with extra headroom for motor starting, ambient heat, and local code rules.
Good to Know
- This math assumes a balanced load, meaning all three phases draw the same current.3
- Large motors started straight across the line often draw six to eight times their normal operating current.2
- Long cable runs add voltage drop. A lower voltage at a motor usually raises the current it needs to carry its load, so the real current can be higher than the plain formula shows.2
- Motor nameplates list output horsepower at the shaft, not input watts.2 Divide by the motor's efficiency for a true input figure.1
- Always follow the NEC, IEC, or your local wiring rules when picking wire and protection sizes.