After installing a new 480 V, 30 kVA, three-phase dry-type transformer, a journeyperson performs a turns ratio test using a TTR (Transformer Turns Ratio) meter. For a transformer with a primary voltage of 480 V and a secondary voltage of 208Y/120 V, what approximate turns ratio should they expect to measure between the H1-H2 terminals and the X1-X2 (phase-to-phase) secondary terminals?

Question: After installing a new 480 V, 30 kVA, three-phase dry-type transformer, a journeyperson performs a turns ratio test using a TTR (Transformer Turns Ratio) meter. For a transformer with a primary voltage of 480 V and a secondary voltage of 208Y/120 V, what approximate turns ratio should they expect to measure between the H1-H2 terminals and the X1-X2 (phase-to-phase) secondary terminals?

Answer options: ✅ 2.31:1

• 1.73:1
• 4.00:1
• 1.15:1

Correct answer: 2.31:1

Explanation: The nominal turns ratio is calculated by dividing the primary phase voltage by the secondary phase voltage. For a 480 V delta primary and 208 V wye secondary, we compare 480 V from line-to-line on the primary to 208 V line-to-line on the secondary. So, 480 V / 208 V = 2.3076, which is approximately 2.31:1. The TTR meter measures this ratio directly.