kVA To Amps Three Phase Converter
Convert a three-phase apparent-power rating in kVA into line current in amps using line-to-line voltage, with kW, phase current and planning margin shown beside the result.
Convert Three-Phase kVA To Current
Three-Phase Current Result
72.17 A
50 kVA at 400 V three phase is 72.17 amps per line before any display margin.
This is a balanced three-phase arithmetic result. Electrical installation, protection and cable work need competent design.
Formula For Three-Phase kVA To Amps
VA = kVA x 1,000amps = VA / (square root of 3 x line-to-line volts)amps = kVA x 1,000 / (1.7320508076 x volts)kW = kVA x power factorThe square-root-of-three term is the key difference between single-phase and three-phase current. A three-phase system spreads power across three lines, so the line current is not calculated by dividing VA by voltage alone. The voltage field must be line-to-line voltage, not line-to-neutral voltage, unless a specialist calculation says otherwise.
Power factor is included only because many users also want a kW comparison. A 50 kVA load at 0.8 power factor is about 40 kW, while the line current from kVA at 400 V remains 72.17 A. If the equipment plate already gives amps, that rating should normally take priority over a converted value because it may include manufacturer limits, cooling or duty cycle.
Common 400 V Three-Phase Values
| kVA | Amps At 400 V | kW At PF 0.8 | Planning Note |
|---|---|---|---|
| 10 | 14.43 A | 8 kW | Small three-phase machine, charger or distribution check. |
| 25 | 36.08 A | 20 kW | Workshop load or small generator comparison. |
| 50 | 72.17 A | 40 kW | Substantial equipment, UPS or transformer note. |
| 100 | 144.34 A | 80 kW | Requires proper supply-capacity and protection review. |
| 250 | 360.84 A | 200 kW | Large distribution calculation, not a plug-in load check. |
Balanced Load And Nameplate Checks
Balanced Three-Phase Loads
The result assumes the three phases share the load evenly. Motors, heaters and balanced industrial equipment can often be treated this way for first-pass arithmetic. Mixed single-phase loads spread across a distribution board may not be balanced, so neutral current and phase loading need a fuller check.
Motors, Drives And Starting Current
A motor can draw much more current while starting than while running. Variable-speed drives, soft starters and inrush limiting can change the supply demand. Use the equipment data sheet for starting, overload and protection checks, not only the converted steady current.
Generators And UPS Ratings
Generators and UPS systems may list standby, prime, continuous, overload and battery-runtime ratings. The kVA value you enter should match the intended use. A short overload rating is not the same as a continuous supply rating.
Worked Examples
A 30 kVA balanced three-phase load at 400 V draws 43.30 A per line. At a power factor of 0.85, the real-power display is 25.5 kW. If a 20% planning margin is shown, the comparison current is 51.96 A. That margin is only a visible planning figure; cable size, protective device choice, grouping, temperature, installation method and voltage drop need a proper design method.
A 125 kVA generator at 415 V gives 173.91 A per line by the same formula. If a site note uses 400 V, the current would be 180.42 A, so the voltage assumption matters. Copy the voltage used in the calculation beside the result. If equipment can run at more than one voltage, make a separate calculation for each supply arrangement.
If the load is a mixture of three-phase and single-phase equipment, calculate the three-phase items separately and check the line loading created by the single-phase items. A neat kVA total can hide one overloaded phase if small loads are not spread sensibly.
When Not To Rely On The Converted Current Alone
Do not use this page to select a breaker, cable, generator, transformer or plug without checking the governing electrical rules and the equipment instructions. The converted current does not know the fault level, earthing arrangement, cable route, ambient temperature, grouping, duty cycle, harmonic content, phase imbalance, voltage drop or disconnection requirement. These items can change a design even when the arithmetic current is correct.
For site handover notes, include the source document, voltage, kVA basis, power factor used for kW display and whether the load is balanced. If the number will be used by someone else, state clearly that it is a conversion result. That small note can prevent a planning figure from being mistaken for an approved installation rating.
Recording The Input Assumptions
A useful three-phase current note should show more than the amp figure. Write the kVA, voltage, phase arrangement, power factor if kW is shown, source of the rating and whether the load is continuous, intermittent or starting-heavy. A future reader may not know whether the number came from a transformer plate, a generator quote, a design schedule or a quick telephone estimate.
If the calculation supports a purchase, add the equipment duty wording. Standby, prime, continuous, temporary, diversified and connected-load ratings are not the same. A generator that can carry a brief peak may not be suitable for the same load all day. A UPS may carry the current but fail the runtime requirement. A distribution board may have enough headline amps but still have a phase-balance problem. Keeping those notes beside the converted current protects the figure from being reused in a context it was not meant for.
Voltage Sensitivity Check
When a current result is close to a limit, test the voltage assumption. A 100 kVA load at 400 V gives a higher current than the same load at 415 V. That difference may affect a quotation, switchgear comparison or generator discussion. Write both cases if the supply voltage is not settled. Add the chosen nominal voltage to any schedule.
FAQ
What is the three-phase kVA to amps formula?
Amps equals kVA multiplied by 1,000, divided by square root of 3 times the line-to-line voltage.
Do I use 400 V or 230 V for UK three-phase?
For a standard low-voltage three-phase line-current calculation, use the line-to-line voltage, commonly 400 V. Use the actual equipment or supply value if it differs.
Does power factor change the amps result?
Not when you start from kVA. kVA already represents apparent power. Power factor is used to show approximate kW.
Can this be used for single-phase?
No. Single-phase uses amps equals kVA times 1,000 divided by volts. It does not use the square-root-of-three factor.
Why is my nameplate current different?
The nameplate may include duty, voltage range, efficiency, cooling, overload or manufacturer limits. Use the nameplate for equipment protection decisions.
Can this size a cable?
No. Cable sizing needs installation method, protective device, voltage drop, thermal limits and fault protection checks by a competent person.
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