What voltage would you read if you cross phase two hot legs on the secondary?

What voltage would you read if you cross phase two hot legs on the secondary?

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

Answer: (A)

In a three-phase system, the voltage you read between two hot legs is the line-to-line voltage. If the secondary is a 120/208 V wye system, each leg to neutral is 120 V, and the line-to-line voltage is V_LL = √3 × V_Ph-N = 120 × √3 ≈ 208 V. So crossing two hot legs on the secondary yields about 208 volts. The other voltages correspond to different configurations: 120 V is leg-to-neutral, 240 V would be for a 120/240 V delta or similar, and 480 V for a 277/480 V system.

In a three-phase system, the voltage you read between two hot legs is the line-to-line voltage. If the secondary is a 120/208 V wye system, each leg to neutral is 120 V, and the line-to-line voltage is V_LL = √3 × V_Ph-N = 120 × √3 ≈ 208 V. So crossing two hot legs on the secondary yields about 208 volts. The other voltages correspond to different configurations: 120 V is leg-to-neutral, 240 V would be for a 120/240 V delta or similar, and 480 V for a 277/480 V system.