In the 480 to 208Y/120-volt transformer example, what is the line-to-line voltage on the secondary?

• A. 208 V
• B. 120 V
• C. 240 V
• D. 277 V

Answer: (A)

In a 208Y/120 V secondary, the three-phase windings are connected in a wye. That means each phase to neutral is 120 V, while the voltage between any two phases (line-to-line) is higher by a factor of sqrt(3). Numerically, 120 V × sqrt(3) ≈ 208 V. So the line-to-line voltage on the secondary is 208 V. The 120 V is what you would read from any phase to the neutral, not between two phases. A system with 277 V line-to-line would be 480Y/277 V, not 208Y/120 V, and 240 V isn’t the specified secondary voltage here.