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 everything is wired and working correctly, what voltage reading would be plausible when you measure the line side of switch to load side of switch? (switch is on)

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 everything is wired and working correctly, what voltage reading would be plausible when you measure the line side of switch to load side of switch? (switch is on)

• A. 120 volts
• B. 23 volts
• C. 0 volts
• D. 240 volts

Answer: (C)

When a simple single-pole switch is on, the hot feed (line) and the switched leg (load) are connected together by the closed switch. That means there’s essentially no voltage difference between those two conductors—the current can flow, and they sit at the same electrical potential. A real switch has a tiny resistance, so you might see a very small voltage across it, but on a typical voltmeter the reading would be essentially zero volts. This is why zero volts is the plausible reading. The other options would only make sense if you were measuring between hot and neutral (120 volts on a 120V system), or if the system were something other than a standard 120V single-phase circuit (like 240 volts, which isn’t the case here). A small nonzero reading like 23 volts isn’t expected for line-to-load on a closed switch.

When a simple single-pole switch is on, the hot feed (line) and the switched leg (load) are connected together by the closed switch. That means there’s essentially no voltage difference between those two conductors—the current can flow, and they sit at the same electrical potential. A real switch has a tiny resistance, so you might see a very small voltage across it, but on a typical voltmeter the reading would be essentially zero volts. This is why zero volts is the plausible reading.

The other options would only make sense if you were measuring between hot and neutral (120 volts on a 120V system), or if the system were something other than a standard 120V single-phase circuit (like 240 volts, which isn’t the case here). A small nonzero reading like 23 volts isn’t expected for line-to-load on a closed switch.