kW To Amps Three Phase Converter
Convert three-phase real power in kW into line current in amps using voltage and power factor, with kVA and a planning margin displayed beside the answer.
Convert Three-Phase kW To Amps
Three-Phase Current Result
50.96 A
30 kW at 400 V three phase and PF 0.85 is 50.96 amps per line.
This assumes a balanced three-phase load and a known power factor. It does not size cables or protection.
Formula For Three-Phase kW To Amps
watts = kW x 1,000amps = watts / (square root of 3 x line volts x power factor)amps = kW x 1,000 / (1.7320508076 x volts x PF)kVA = kW / PFThree-phase kW to amps needs both the square-root-of-three factor and the power factor. The square-root-of-three term comes from the relationship between line voltage and phase power in a balanced three-phase system. Power factor is needed because kW is real power while current is linked to apparent power.
If power factor is unknown, the result can move a lot. At 400 V, 30 kW and PF 1.0 is 43.30 A. At PF 0.8, the same kW becomes 54.13 A. That difference can affect supply planning, generator loading and voltage drop checks, so it should not be hidden.
400 V Examples With Different Power Factors
| kW | PF | Amps At 400 V | kVA |
|---|---|---|---|
| 15 | 0.85 | 25.48 A | 17.65 kVA |
| 30 | 0.85 | 50.96 A | 35.29 kVA |
| 30 | 1.00 | 43.30 A | 30.00 kVA |
| 75 | 0.80 | 135.32 A | 93.75 kVA |
| 150 | 0.90 | 240.56 A | 166.67 kVA |
Where This Conversion Is Useful
Motor Schedules
A motor schedule may list kW because it is concerned with mechanical output or real input power. Current still depends on voltage, efficiency, power factor and starting method. Use the plate current for final checks where available.
Generators And Site Supplies
When a generator quote is in kVA but the load list is in kW, this page helps expose the apparent-power demand. A poor power factor can use more generator capacity than a kW-only list suggests.
Distribution Board Planning
For early load schedules, the calculation gives a line-current estimate. The next checks are phase balance, diversity, cable route, voltage drop, protective device rating and any harmonic-producing equipment.
Worked Examples
A 45 kW balanced three-phase load at 400 V and PF 0.9 draws 72.17 A per line. Apparent power is 50 kVA. If the same 45 kW load had PF 0.75, current would rise to 86.60 A and apparent power would be 60 kVA. The real work done by the load is the same, but the supply current is not.
A 75 kW industrial machine at 415 V and PF 0.85 draws 122.68 A per line. At 400 V it draws 127.38 A. That difference is not dramatic, but it is large enough to matter near a rating boundary. Always keep the voltage assumption beside the result.
A group of mixed loads can be harder. Three balanced 10 kW heaters at PF 1.0 can be modelled neatly. A workshop with welders, compressors and single-phase sockets cannot be summarised by one kW figure without checking how loads are distributed and how often they run together.
Safety And Design Boundaries
The converter does not decide whether equipment can be connected. It does not check earthing, fault current, protective device type, cable size, thermal limit, grouping, ambient temperature, harmonics, leakage current, motor starting, duty cycle or local rules. These are design questions, and the arithmetic current is only one input.
If the result is used in a quotation or handover pack, state whether it is based on assumed PF or measured PF. A contractor reading the figure later needs to know whether it came from a manufacturer’s data sheet, a design schedule or a quick planning assumption. For fixed wiring, high current or safety-critical equipment, get competent electrical advice.
Load Lists And Phase Balance
Three-phase kW figures often appear in early load lists. A load list may add motors, heaters, chargers, pumps, fans and sockets into one total, but the supply does not only care about the total. It also cares which phase carries each load, whether loads run together, how often motors start and whether electronic equipment produces harmonics. A tidy kW total can still leave one phase overloaded.
Use this converter for each major balanced three-phase load, then list single-phase loads separately. If a board has many single-phase circuits, show the phase allocation rather than hiding everything in one total kW line. For generators, include the largest motor start and the largest load step. For variable-speed drives, include manufacturer input current and harmonic guidance where supplied.
When the result is close to a protective-device or supply boundary, do not round in the hopeful direction. Change one input at a time: voltage, power factor, margin and kW. This sensitivity check shows whether the result is stable or depends on an optimistic assumption.
Power Factor Assumption Notes
Power factor should not be treated as decorative. If the load list uses 0.8 because no data is available, label it as assumed. If the equipment data gives 0.92 at full load, use that value but note that part-load behaviour may differ. For drives and power supplies, ask whether the quoted figure is displacement power factor, total power factor or a corrected input rating.
Where a site has penalties or capacity limits based on kVA, the kVA result can be as important as the amp result. A load may meet a kW expectation while still using too much apparent power. Keep kW, PF, kVA and amps together in the same row so the trade-off is visible. If measured current later becomes available, keep the measured value beside the calculated one and record the load condition at the time.
Measured Current Follow-Up
If measured current later becomes available, keep it beside the calculated current and record whether the equipment was at full output.
FAQ
What is the three-phase kW to amps formula?
Amps equals kW multiplied by 1,000, divided by square root of 3 times line voltage times power factor.
Why does PF matter here?
Because kW is real power. Lower PF means more apparent power and more current for the same kW.
Can I use 230 V in this converter?
Only if 230 V is the correct line-to-line voltage for your three-phase system. For many UK low-voltage three-phase calculations, 400 V is the line-to-line value.
Is the result per phase or total?
It is the line current for a balanced three-phase load. It is not three times the line current.
What if the equipment gives kVA instead of kW?
Use a kVA to amps converter. Do not apply power factor twice.
Can this size a generator?
It helps compare load current and kVA, but generator selection also needs starting current, load steps, duty rating and manufacturer guidance.
Sources
- Health and Safety Executive. (n.d.). Electrical safety at work. HSE. https://www.hse.gov.uk/electricity/
- Institution of Engineering and Technology. (n.d.). Wiring Regulations. IET. https://electrical.theiet.org/bs-7671/
- International Bureau of Weights and Measures. (2019). The International System of Units (SI), 9th edition. BIPM. https://www.bipm.org/en/publications/si-brochure