kVA to Amps Calculator

Transformers, generators and uninterruptible power supplies are all rated in kilovolt-amperes rather than kilowatts, and the reason is thermal. What wears out a winding is the heat produced by the current passing through it. That heating happens whether or not the current is doing anything useful at the far end, so the honest rating for a piece of equipment is the total current it can pass at its rated voltage — which is exactly what a kVA figure states.

Apparent power is that product: volts times amps, with no allowance for phase relationship. Rearranged for current, and with the kilo multiplied out, it gives the whole conversion:

Single phase: I = (kVA × 1,000) ÷ V
Three phase: I = (kVA × 1,000) ÷ (V × 1.732)

Notice what is absent. There is no power factor term anywhere in either line, and adding one is the mistake this page exists to head off. Power factor describes the relationship between apparent power and real power; a kVA rating is already on the apparent side of that relationship, so dividing by power factor moves the answer somewhere neither quantity lives. The result is a current figure inflated by roughly 1/PF — around 25% at a power factor of 0.8, which is enough to buy the wrong cable.

The 1.732 on three phase is the square root of three, and it belongs to the geometry of a three-phase system rather than to any code. Enter the line-to-line voltage alongside it: 208 or 480 in North American practice, 400 in most of Europe and Australia.

One more thing the formula assumes and the nameplate does not always say. On a transformer, the rating applies to both windings, but the voltage does not — so a single unit has two full-load currents that can differ by a factor of two or more. The converter answers for whichever winding voltage you give it, which means the voltage field is doing more work here than on any other page in this set.

A 75 kVA dry-type transformer stepping 480 V down to 208 V, three phase — the same unit the transformer sizing calculator works through, so the two pages can be read against each other.

Start on the primary. The rating is 75 kVA, which is 75,000 VA. The winding is 480 V, and it is three phase, so the divisor is 480 × 1.732 = 831.36. That gives 75,000 ÷ 831.36 = 90.21 A. This is the current the supply-side conductors carry and the basis for the primary overcurrent device under 450.3(B).

Now the secondary, same unit, same rating. The only thing that has changed is the voltage: 208 × 1.732 = 360.26, and 75,000 ÷ 360.26 =208.2 A. One transformer, one nameplate, and two currents that differ by a factor of 2.3.

That ratio is not a coincidence — it is the voltage ratio, 480 ÷ 208, turned upside down. A transformer moves a fixed quantity of apparent power, so lowering the voltage on one side necessarily raises the current on that side in exact proportion. Any answer where the low-voltage side carries less current than the high-voltage side is wrong before you check the arithmetic.

What would happen if power factor were applied. Suppose the load is a plant running at 0.8 and the temptation is to divide by it. The primary figure becomes 112.8 A rather than 90.21 A. Nothing about the transformer has changed; a 75 kVA unit at 480 V cannot pass 112.8 A whatever the load does, because 112.8 A at that voltage would be 93.8 kVA and the winding would be running 25% over its rating. The number is not merely conservative — it describes a machine that does not exist.

Use this table when you have a rating in hand and want the current at one of the four common supplies without opening anything. It is faster than the converter for the ratings that appear on most jobs, and it puts the four answers for a given machine side by side — which the converter, answering one voltage at a time, cannot.

Read across a single row and the pattern that governs every kVA conversion is visible at once. The 120 V figure is always twice the 240 V one, because halving the voltage doubles the current. The 208 V three-phase figure is smaller than the 240 V single-phase one despite the lower voltage, which surprises people until they remember the 1.732 in the denominator doing the work.

The equipment column matters more than it looks. Transformer ratings are continuous thermal ratings and the current shown is genuinely available all day. Generator and UPS ratings usually sit alongside a separate kW figure that will bind first on a high power factor load, so treat those rows as the current the output conductors must be able to carry rather than as capacity you can count on selling.

Ratings below 15 kVA are UPS and small generator sizes; the rest is the standard transformer ladder. Neither list is a code table — they are what manufacturers build, and a particular line may not offer every rung.