A 15-amp, single-phase circuit runs from the panel to a bedroom and only energizes all the receptacles and the incandescent light in that bedroom. Assuming proper wiring, what voltage reading is plausible when you measure the line side of switch to load side of switch? (switch is off)

A 15-amp, single-phase circuit runs from the panel to a bedroom and only energizes all the receptacles and the incandescent light in that bedroom. Assuming proper wiring, what voltage reading is plausible when you measure the line side of switch to load side of switch? (switch is off)

• A. 91 volts
• B. 120 volts
• C. 0 volts
• D. 240 volts

Answer: (B)

The main idea is what you measure across an open switch in a typical bedroom branch circuit. The line side is the hot supply, while the load side goes to the light fixture and then to neutral. With the switch open, no current can flow, so there’s no voltage drop across the light fixture. That means the load side is effectively at neutral potential, while the line side stays at hot. The voltage between line and load sides is then essentially the full supply voltage, about 120 volts in a standard residential 120 V circuit. So a reading of 120 volts is the plausible result.

The main idea is what you measure across an open switch in a typical bedroom branch circuit. The line side is the hot supply, while the load side goes to the light fixture and then to neutral. With the switch open, no current can flow, so there’s no voltage drop across the light fixture. That means the load side is effectively at neutral potential, while the line side stays at hot. The voltage between line and load sides is then essentially the full supply voltage, about 120 volts in a standard residential 120 V circuit. So a reading of 120 volts is the plausible result.