Transformer Calculator

Primary and secondary current from kVA rating, voltages, and phase

Transformer Parameters

Phase

Input Method

Transformer kVA

Primary Voltage (V)

Secondary Voltage (V)

Transformer Rating

75 kVA

Primary FLA

480V 3Ø

90.2A

Secondary FLA

208V 3Ø

208.2A

Primary OCPD

NEC 450.3 (≤125% FLA)

125A

Turns Ratio

Primary : Secondary

2.31 : 1

I₁ = kVA × 1000 / (V₁ × 1)

I₁ = kVA × 1000 / (V₁ × √3)

I₂ = kVA × 1000 / (V₂ × 1)

I₂ = kVA × 1000 / (V₂ × √3)

NEC 450.3(B): Primary OCPD ≤ 125% of primary FLA (if secondary has OCPD).

Secondary panel: main breaker ≤ 125% of secondary FLA for supervised locations.