In a three-phase system, what is the line-to-line voltage for the standard secondary system?

In a three-phase system, what is the line-to-line voltage for the standard secondary system?

• A. 208 volts
• B. 120 volts
• C. 277 volts
• D. 69 kV

Answer: (A)

Line-to-line voltage in a balanced three-phase wye system is the vector difference between two phase voltages, which equals the line-to-neutral voltage times sqrt(3). For the standard secondary configuration, each line-to-neutral voltage is 120 V, so the line-to-line voltage is 120 × sqrt(3) ≈ 207.8 V, commonly rounded to 208 V. This is the voltage you measure between any two lines. The line-to-neutral value of 120 V is used for single-phase loads, 277 V would be the line-to-neutral voltage for a 480Y/277 system (not the line-to-line voltage of the 120/208 system), and 69 kV is a high-voltage primary level, not a standard secondary distribution voltage.

Line-to-line voltage in a balanced three-phase wye system is the vector difference between two phase voltages, which equals the line-to-neutral voltage times sqrt(3). For the standard secondary configuration, each line-to-neutral voltage is 120 V, so the line-to-line voltage is 120 × sqrt(3) ≈ 207.8 V, commonly rounded to 208 V. This is the voltage you measure between any two lines. The line-to-neutral value of 120 V is used for single-phase loads, 277 V would be the line-to-neutral voltage for a 480Y/277 system (not the line-to-line voltage of the 120/208 system), and 69 kV is a high-voltage primary level, not a standard secondary distribution voltage.