A transformer name plate lists 2400/4160; 120/240. What is the voltage required by the primary winding?

• A. 120
• B. 4160
• C. 2400
• D. 240

Answer: (C)

Primaries are the windings connected to the supply, and a nameplate shows the voltages for those windings. Here, the left-hand numbers (before the semicolon) are the primary voltages: 2400/4160 V. The right-hand numbers (after the semicolon) are the secondary voltages: 120/240 V. The slash indicates the primary has two tapping options, so you can connect for either 2400 V or 4160 V depending on how the windings are wired. The problem’s standard or typical configuration uses 2400 V on the primary, with a higher voltage option available if you wire the primaries in series for 4160 V. So the voltage required by the primary winding for normal operation is 2400 V.