A 15-amp, single-phase circuit runs from the panel to a bedroom and only energizes the receptacles and the lighting in that bedroom. Assuming proper wiring, what is a plausible voltage reading when measuring the receptacle phase conductor to ground?

A 15-amp, single-phase circuit runs from the panel to a bedroom and only energizes the receptacles and the lighting in that bedroom. Assuming proper wiring, what is a plausible voltage reading when measuring the receptacle phase conductor to ground?

• A. 0 volts
• B. 78 volts
• C. 120 volts
• D. 240 volts

Answer: (C)

In a typical home electrical system, the panel supplies two hot legs that are 180 degrees out of phase, giving 120 volts from any one hot conductor to neutral (and to the grounding conductor, since ground is bonded to neutral at the service). A bedroom circuit that powers receptacles and lighting uses one hot and neutral, with ground tied to the service equipment. So measuring from the hot (phase) conductor to ground, you’d expect about 120 volts under proper wiring. The other numbers don’t fit: 0 volts would mean no voltage difference, and 240 volts would be hot-to-hot, not hot-to-ground. 78 volts is not a normal line-to-ground value in this system.

In a typical home electrical system, the panel supplies two hot legs that are 180 degrees out of phase, giving 120 volts from any one hot conductor to neutral (and to the grounding conductor, since ground is bonded to neutral at the service). A bedroom circuit that powers receptacles and lighting uses one hot and neutral, with ground tied to the service equipment. So measuring from the hot (phase) conductor to ground, you’d expect about 120 volts under proper wiring. The other numbers don’t fit: 0 volts would mean no voltage difference, and 240 volts would be hot-to-hot, not hot-to-ground. 78 volts is not a normal line-to-ground value in this system.