On a 120/240 V split-phase service, what is the voltage from phase to ground for either hot leg?

On a 120/240 V split-phase service, what is the voltage from phase to ground for either hot leg?

• A. 240
• B. 277
• C. 120
• D. 0

Answer: (C)

In a 120/240 V split-phase service, each hot leg is 120 V to neutral (which is bonded to ground at the service equipment). The two hot legs are 180 degrees out of phase, so the voltage between them is 240 V. Because ground and neutral are at the same potential at the panel, the voltage from either hot leg to ground is essentially the same 120 V you’d see from hot to neutral. The other numbers don’t fit this setup: 240 V is the line-to-line voltage, not hot-to-ground; 277 V would be for a 277/480 V wye system; 0 V would imply the conductor is at ground potential, which isn’t the case for a hot leg. Therefore, the voltage from phase to ground for either hot leg is 120 V.

In a 120/240 V split-phase service, each hot leg is 120 V to neutral (which is bonded to ground at the service equipment). The two hot legs are 180 degrees out of phase, so the voltage between them is 240 V. Because ground and neutral are at the same potential at the panel, the voltage from either hot leg to ground is essentially the same 120 V you’d see from hot to neutral. The other numbers don’t fit this setup: 240 V is the line-to-line voltage, not hot-to-ground; 277 V would be for a 277/480 V wye system; 0 V would imply the conductor is at ground potential, which isn’t the case for a hot leg. Therefore, the voltage from phase to ground for either hot leg is 120 V.