Full load current calculator
Calculate full load current from power, voltage and phase.
Try a job 6
Each job fills in example values. Replace them with your values.
- Find a 22 kW motor's full load currentThe line current a 22 kW three phase motor takes at 400 V.
- Find the current of a 7.2 kW chargerThe current of a single‑phase 7.2 kW load.
- Find the current of 100 kVAThe line current of a 100 kVA load at 400 V.
- Find the current of a 3 kW heaterThe current of a 3 kW heater at 230 V.
- Find the current of a chillerThe current of a 45 kW chiller at 0.85 power factor.
- Find the current of a commercial ovenThe current of a 15 kW three‑phase oven.
Inputs
A worked example with the default inputs.
- Phases
- Three phase
- Voltage
- 400 V
- Rating unit
- kW
- Rating
- 15
- Power factor
- 0.9
- Efficiency
- 1
Full load current
24.06A
- Apparent power drawn
- 16.67kVA
- Output power
- 15kW
This result is a design aid. Verify it against the current standard.
Calculation steps
- Output power15kW
- Apparent power drawn16.67kVA
- Full load currentResult24.06A
About this calculator
How this is calculated
The tool works out the full load current of a load. It uses the power, the voltage, the power factor and the efficiency. It works on one phase or three. It reads no table, so it cites no clause.
- Supply. You pick one phase or three and enter the voltage. The voltage you enter sets the divisor in the last step.
- Output power. You enter the load in kW or kVA. For a kW load, the tool takes this as the output power.
- Apparent power drawn. It divides the output power by the efficiency and by the power factor. A kVA entry skips the power factor step.
- Full load current. On one phase, it divides the apparent power by the voltage. On three phases, it divides by the voltage and by the square root of three.
On three phases, enter the line voltage, such as 400 V. On one phase, enter the phase voltage, such as 230 V.
Worked example
- A 15 kW three‑phase load at 400 V. The power factor is 0.9 and the efficiency is 1. The apparent power drawn is 16.67 kVA. The full load current is 24.06 A.
Limits
The result is the steady running current. It is not the starting current. A motor draws more current at start. Use the motor tool for the starting current.
The tool assumes a balanced load on three phases. It does not add a margin for the cable or the breaker. Size the cable from the design current with the cable size calculator. The tool gives no harmonic or neutral current.
Efficiency is a value between 0 and 1. A kVA entry is already an apparent power, so the tool does not divide it by the power factor.
Check the efficiency you enter. A motor rating in kW is a shaft output, so enter the motor efficiency. A resistive heater has an efficiency of 1. Check the power factor on the nameplate. A low power factor raises the current for the same kW.
See also: Commercial kitchen kW to amps, Three‑phase power kVA to amps at 400 V and the three‑phase power tool.
Questions
The result is a design aid. Verify against the current standard.
What does the full load current calculator do?
The tool converts a load rating into a current. Enter the rating in kilowatts or in kilovolt amperes, the voltage and the phase count. It reports the load's full load current, its real power and its apparent power.
Which inputs matter most?
The rating and the voltage set the current. For a kilowatt rating, the power factor and the efficiency both raise the apparent power, so both raise the current. For a kilovolt ampere rating the efficiency is not applied. A three phase result divides by the square root of three.
What does this tool not do?
It does not size a cable or a protective device. It cites no standard table, because the result is a direct calculation. Use the current it gives as the design current in the cable size tool. The inputs sit in the page address, so a link reproduces the result.
Worked examples
- Commercial kitchen kW to amps full load currentTurning a 30 kW commercial kitchen nameplate load into 45.58 A at 400 V three phase, with the power factor step that a plain kW to amps sum leaves out.
- Ohm's law on a 3 kW water heater elementWork the current and working resistance of a 3 kW, 230 V water heater element with Ohm's law, why a cold meter reading is lower, then a 9 kW three‑phase bank.
- Motor circuit for a 15 kW pump: DOL or star-deltaSize a 15 kW 400 V pump circuit: cable, breaker, contactor and overload relay. Compare DOL, star-delta, soft starter and drive starts.
- 22 kW EV charger amps at 400 V three‑phaseA 22 kW three‑phase EV charger draws 31.75 A at 400 V. See the inputs, the clause, the arithmetic and the current that feeds cable sizing and demand.
Background
- Ohm's law and power on d.c. and a.c.Ohm's law and the power formulas on d.c., single‑phase and three‑phase a.c.: how power factor and impedance change them, and how any two values give the rest.
- Control panels and PLC wiringSegregation of LV and ELV in a control panel, terminal and numbering practice, panel earthing, and the 24 V DC voltage drop that long instrument loops fail on.
- Motor circuits and startingHow full load current sizes the cable and starting current sizes the device on a motor circuit, with a worked 22 kW 400 V motor and the cable the tool selects.
- Power factor and reactive powerWhat power factor is, why a low one costs current and capacity, how a capacitor bank corrects it in steps, and when harmonics call for a detuned bank.
- Industrial switchboards: fault rating, form, IPWhat the three ratings on an industrial switchboard or motor control centre mean, how each one is chosen, and which AmpSize tools feed the numbers behind them.
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