What is this kW to ampere tool used for?
This tool estimates line current from active power for single-phase, three-phase and DC systems.
It is useful for first-pass checks in breaker selection, preliminary cable sizing, panel load schedules and site surveys.
Formulas used
- Single-phase: I = P / (V x cos phi x eta)
- Three-phase: I = P / (sqrt(3) x V x cos phi x eta)
- DC: I = P / (V x eta)
Variables and meaning
- P
- Active load power or the power value associated with the equipment.
- V
- Line voltage or system voltage level.
- cos phi
- Power factor used in AC systems to relate active power to apparent power.
- eta
- Efficiency factor; include it when converting output power into required input current.
- I
- Calculated line current.
Unit reference tables
Power units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Watt (W) | W | 1 W | Base SI heat-transfer-rate unit |
| Kilowatt (kW) | kW | 1,000 W | Larger heat loads |
| Megawatt (MW) | MW | 1,000,000 W | Very large heat-transfer rates |
| Kilocalorie per hour (kcal/h) | kcal/h | 1.16222222222 W | Legacy heat-load and process calculations |
| Btu per hour (Btu/h) | Btu/h | 0.293071070172 W | HVAC and Imperial/US heat loads |
Voltage units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Millivolt (mV) | mV | 0.001 V | Sensors and low-level signals |
| Volt (V) | V | 1 V | Base SI voltage unit |
| Kilovolt (kV) | kV | 1,000 V | High-voltage transmission |
Current units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Milliampere (mA) | mA | 0.001 A | Electronic circuit currents |
| Ampere (A) | A | 1 A | Base SI current unit |
| Kiloampere (kA) | kA | 1,000 A | Industrial power systems |
Worked examples
5.5 kW, 400 V, three-phase, 0.9 power factor and 92 efficiency
I = 5500 / (1.732 x 400 x 0.9 x 0.92) which gives about 9.59 A.
2 kW, 230 V single-phase, 0.95 power factor and 100 efficiency
I = 2000 / (230 x 0.95) which gives about 9.15 A.
Typical applications
- Preselection of breakers and fuses
- Preliminary cable-sizing checks
- Load-schedule validation
- Generator, UPS and switchboard planning
Assumptions and limitations
- This tool gives an approximate line current and does not include harmonics, starting current, ambient-temperature derating or cable correction factors.
- In the three-phase mode, the voltage input is interpreted as line-to-line voltage.
- If the entered power already represents electrical input power, set efficiency to 1 or 100.