Every transformer, DG set and UPS nameplate shows kVA, but cables, breakers and CTs are chosen in amperes. This page shows the exact formulas, ready tables for Indian voltages and worked examples you can repeat on site.
Converting kVA to current is the first step in sizing cables, breakers and CTs for any transformer or generator. Learn the formulas, the shortcuts engineers use at 415 V and 11 kV, and the mistakes that give wrong answers.
What Is kVA to Amps Conversion?
kVA to amps conversion finds the line current that a load or source of known apparent power draws at a given voltage. For single phase I = kVA × 1000 ÷ V, and for 3 phase I = kVA × 1000 ÷ (√3 × VLL), where VLL is the line to line voltage.
- Single phase: I = kVA × 1000 ÷ V
- 3 phase: I = kVA × 1000 ÷ (1.732 × VLL)
- At 415 V, 3 phase, current is about 1.39 A for every kVA
- At 11 kV, 3 phase, current is about 0.0525 A for every kVA
- Power factor is not needed, because kVA already includes it
The kVA figure is apparent power, the product of voltage and current, so no power factor enters this formula. If you start from kW instead, divide by power factor first, as shown in our page on power factor, kW, kVA and kVAR.
A 1000 kVA, 11 kV distribution transformer like this one carries only about 52.5 A on its HV side but about 1391 A on a 415 V LV side. That huge ratio is why current is always worked out separately for each winding.
kVA to Amps Formula for Single Phase and 3 Phase
The kVA rating is simply volts times amps divided by 1000, so the current is found by rearranging that product. Hammond Power Solutions prints exactly these two expressions on its full load current cards for dry type transformers.
I (A) = kVA × 1000 ÷ V
3 phase (balanced)
I (A) = kVA × 1000 ÷ (√3 × VLL)
√3 = 1.732
In the 3 phase formula VLL is the line voltage, such as 415 V, 433 V or 11 kV, and the result is the current in each line conductor. Use the phase voltage of 240 V instead only when you work with one phase of a star system and one third of the kVA.
Divide kVA × 1000 by the supply voltage. A 5 kVA inverter at 230 V draws 21.74 A.
Divide by 1.732 × line voltage. The standard method for transformers, DG sets and motors.
Take one third of kVA and divide by phase voltage. It gives the same answer for a star load.
There is no kVA in DC, just kW. Current is kW × 1000 ÷ V with no √3.
Indian distribution transformers are usually specified with a no load LV voltage of 433 V, not 415 V. Using 433 V gives a slightly lower current, so many engineers use 415 V to stay on the safe side when sizing cables.
For a quick feel, remember the per kVA multipliers in the next section. They let you check a cable or breaker selection in your head before you open any software.
kVA to Amps Table for 415 V, 433 V and 11 kV
The table below uses the 3 phase formula for common Indian transformer and DG set ratings. Values are full load line currents rounded to one or two decimals.
| Rating (kVA) | 415 V (A) | 433 V (A) | 11 kV (A) | 33 kV (A) |
|---|---|---|---|---|
| 62.5 | 86.95 | 83.34 | 3.28 | 1.09 |
| 100 | 139.12 | 133.34 | 5.25 | 1.75 |
| 160 | 222.59 | 213.34 | 8.40 | 2.80 |
| 250 | 347.80 | 333.34 | 13.12 | 4.37 |
| 315 | 438.23 | 420.01 | 16.53 | 5.51 |
| 500 | 695.60 | 666.69 | 26.24 | 8.75 |
| 630 | 876.46 | 840.02 | 33.07 | 11.02 |
| 1000 | 1391.21 | 1333.37 | 52.49 | 17.50 |
| 1600 | 2225.93 | 2133.40 | 83.98 | 27.99 |
| 2000 | 2782.41 | 2666.74 | 104.97 | 34.99 |
| 2500 | 3478.01 | 3333.43 | 131.22 | 43.74 |
Ratings from 62.5 kVA to 500 kVA are typical for diesel generator sets, while 250 kVA to 2500 kVA covers most plant distribution transformers. For LT side cable selection, read this table together with our guide on cable size for load current.
| Single Phase kVA | 230 V (A) | 240 V (A) |
|---|---|---|
| 1 | 4.35 | 4.17 |
| 3 | 13.04 | 12.50 |
| 5 | 21.74 | 20.83 |
| 7.5 | 32.61 | 31.25 |
| 10 | 43.48 | 41.67 |
| 15 | 65.22 | 62.50 |
For 415 V 3 phase, multiply kVA by 1.39 to get amps. For 11 kV multiply by 0.0525, and for single phase 230 V multiply by 4.35, then round up when choosing a breaker.
Solved Examples of kVA to Amps
The first example uses the same defaults as the calculator further below, so you can verify each step. The second works out both windings of a distribution transformer.
I = 400 × 1000 ÷ (1.732 × 415)
I = 400000 ÷ 718.8
I = 556.48 A per line
HV: 1000000 ÷ (1.732 × 11000)
= 52.49 A
LV: 1000000 ÷ (1.732 × 433)
= 1333.37 A
Notice that the current ratio of the two windings, 1333.37 ÷ 52.49, equals the voltage ratio of about 25.4. That is the same relationship our article on transformer turns ratio and secondary voltage explains from the winding side.
I = 10 × 1000 ÷ 230
I = 43.48 A
A 10 kVA single phase UPS therefore needs an input circuit rated above 43.48 A, plus the margin for battery charging. Our page on UPS capacity kVA calculation shows how the load side figure is found in the first place.
How to Convert Amps to kVA
The reverse conversion is used when you clamp a feeder and want to know how much of a transformer is being used. Just multiply voltage and current and divide by 1000, adding √3 for 3 phase.
3 phase: kVA = 1.732 × VLL × I ÷ 1000
Example: 415 V, 300 A
kVA = 1.732 × 415 × 300 ÷ 1000 = 215.6 kVA
If a 250 kVA transformer shows 300 A on each LV phase, it is loaded to about 86 % of its rating. Using the average of three phase currents is fine for a quick check, but large unbalance needs a closer look at the neutral conductor and harmonics.
Where kVA to Amps Is Used in Plants
For generators, first add up the running and starting loads, as explained in how to calculate generator size for an industrial load. Once the kVA is fixed, the kVA to amps step gives the alternator breaker rating.
For transformers, the same thinking runs from the load list to the transformer kVA rating and then to LV and HV currents. The basic winding theory behind these ratings is covered in this transformer working principle guide on our sister site.
The current from kVA to amps is only the normal full load current. The fault current at the same LV bus can be about 20 times higher for a transformer with 5 % impedance, which is why breaker breaking capacity is checked separately.
You can estimate that fault level with our guide to calculating short circuit fault current. Both numbers, full load and fault current, are needed before an LT panel can be specified.
kVA to Amps Calculator
Enter the rating in kVA, the line voltage and the number of phases. The calculator applies the √3 factor for 3 phase and shows the current in each line.
The default 400 kVA at 415 V gives 556.48 A, matching Example 1 above. Try 11000 V to see how small the HV current becomes for the same rating.
Common Mistakes in kVA to Amps
Another frequent mistake is mixing up single phase and 3 phase formulas, a point Industrial Monitor Direct also lists as the most common error. If you are unsure which system you have, read our comparison of single phase and three phase power.
When clamping a 3 phase feeder, measure all three line currents and use the highest one for loading checks. The average hides a heavily loaded phase that may already be running hot.
- Matches how transformers and DG sets are rated
- No need to know load power factor
- Gives the true current that heats cables and windings
- Works for any load type, motor or electronic
- Line vs phase voltage confusion
- Using 433 V when the bus actually sits near 400 V
- Ignoring harmonic current in the neutral
- Forgetting motor starting current is 6 to 7 times higher
Motor starting is a separate check, and our article on motor full load current explains why the running current alone is not enough. A voltage dip study is also wise when a large motor starts on a DG set.
Field Checklist Before Using the Result
- Confirm the nameplate kVA and rated voltage of each winding
- Use line voltage with the √3 formula for 3 phase
- Round the current up to the next standard breaker size
- Derate cable for ambient, grouping and depth
- Check voltage drop on long runs with the full load current
- Compare full load current with the CT primary rating
- Check breaker breaking capacity against fault level, not load current
Long feeders also need a voltage drop calculation using the current you just found. For a plant wide view, combine the feeder currents with a maximum demand calculation with diversity before fixing the main incomer.
Keep the 100 essential engineering formulas sheet handy, since it puts the kVA, kW and current relations on one page. It saves time during commissioning when you need a quick figure.
kVA to Amps FAQ
At 230 V single phase, 1 kVA draws about 4.35 amperes of current. At 415 V in a 3 phase system, the same 1 kVA draws only about 1.39 amperes per line.
The reason is that 3 phase power is shared by three conductors and multiplied by root three. That is why the voltage and phase must always be stated before converting.
Multiply the kVA value by 1000 and divide by 1.732 times the line voltage. For a 500 kVA transformer at 415 V, the current works out to about 695.6 amperes.
Use the line to line voltage, not the phase voltage, with this formula. If you only have the phase voltage, divide one third of the kVA by it instead.
A 100 kVA transformer at 415 V carries about 139 amperes on each low voltage line. On the 11 kV primary side, the same transformer carries only about 5.25 amperes.
The power is the same on both windings, so current falls as voltage rises. The kVA to amps formula simply applies once for each winding voltage.
At 433 V the full load current of a 1000 kVA transformer is about 1333 amperes. At a 415 V working voltage it rises to about 1391 amperes per line.
On the 11 kV side the current is close to 52.5 amperes per line. These values decide the size of the incomer breaker, the busbar and the current transformers.
No, power factor is not needed because kVA already represents voltage times current. Power factor only matters when you convert between kilowatts and kilovolt amperes.
If you start with kilowatts, divide by the power factor to get kVA first. After that, apply the normal current formula for single phase or three phase systems at the rated voltage.
A 62.5 kVA generator at 415 V three phase can supply about 87 amperes per line. This is the rated alternator current at its standard 0.8 power factor rating.
Engine power limits the kilowatts, while the alternator winding limits the current. Running above this current overheats the winding even when the kilowatt reading looks low.
Related Articles
- How to Calculate Transformer kVA Rating
- How to Calculate Generator Size for an Industrial Load
- Power Factor, kW, kVA and kVAR
- How to Calculate Three Phase Power
- Cable Size for Load Current
External References
- Hammond Power Solutions: Transformer Full Load Current Cards (PDF)
- Industrial Monitor Direct: Transformer kVA to Amps 3 Phase Calculation
- Wikipedia: Volt ampere
What We Learn Today
- The kVA to amps formula is kVA × 1000 ÷ V for single phase and kVA × 1000 ÷ (1.732 × V) for 3 phase systems.
- At 415 V each kVA draws about 1.39 A, while at 11 kV each kVA draws only about 0.0525 A per line conductor.
- Power factor is not needed for this conversion, but cable derating, voltage drop and fault level must still be checked separately.