In a wye-connected transformer, how does line current relate to phase current?

• A. Line current equals phase current.
• B. Line current equals √3 times phase current.
• C. Line current equals phase current divided by √3.
• D. Line current equals twice the phase current.

Answer: (A)

In a wye-connected transformer, each line is connected directly to one end of a phase winding, with the other end tied to neutral. The current in that line must flow through that winding, so the line current is the same as the phase current. If the load is balanced, the three phase currents have the same magnitude (though 120 degrees apart), so the line currents match those winding currents in magnitude as well. The √3 factor only appears in delta configurations, where a line current is the vector sum of two winding currents, giving a line current of √3 times a phase current. So the line current equals the phase current.