Which secondary voltage is commonly used for large commercial three-phase distribution?

Which secondary voltage is commonly used for large commercial three-phase distribution?

• A. 120/240 volts
• B. 120/208 volts
• C. 240/480 volts
• D. 277/480 volts

Answer: (D)

In large commercial three-phase distribution, a 480Y/277 V secondary is standard. This means the system is wired in a wye so you get 480 V between any two lines (line-to-line) and 277 V from each line to neutral (line-to-neutral). This combination works well because the 480 V line voltage lets you run heavy equipment and motors with lower currents, improving efficiency and reducing conductor sizes. At the same time, 277 V is a convenient, widely used voltage for lighting and other single-phase loads that can tap the neutral. The other options represent voltages more typical of residential or smaller commercial setups and don’t align with the common large-building distribution practice.

In large commercial three-phase distribution, a 480Y/277 V secondary is standard. This means the system is wired in a wye so you get 480 V between any two lines (line-to-line) and 277 V from each line to neutral (line-to-neutral). This combination works well because the 480 V line voltage lets you run heavy equipment and motors with lower currents, improving efficiency and reducing conductor sizes. At the same time, 277 V is a convenient, widely used voltage for lighting and other single-phase loads that can tap the neutral. The other options represent voltages more typical of residential or smaller commercial setups and don’t align with the common large-building distribution practice.