This transformer current calculator finds the primary and secondary current from the transformer’s kVA rating and its voltages. Enter the rating and voltages above for single- or three-phase.
Formulas
Single phase: I = VA ÷ V Three phase: I = VA ÷ (√3 × VL)
Apply each formula with the primary voltage for primary current, and the secondary voltage for secondary current.
Example
15 kVA, 480 V → 240 V, single phase: primary = 15,000 ÷ 480 = 31.3 A; secondary = 15,000 ÷ 240 = 62.5 A.
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Frequently Asked Questions
How do I calculate transformer current?
Divide the transformer VA by the voltage. For single phase, current equals VA divided by volts; for three phase, divide by the square root of 3 times line voltage.
What is primary vs secondary current?
Primary current is on the supply side, secondary on the load side. Each equals the VA rating divided by that side’s voltage.
Does a step-down transformer increase current?
Yes. As voltage drops on the secondary, current rises proportionally, since VA stays about the same.