On an SPST switch in the open position with 120VAC applied, what would the multimeter read across the switch?

When a single-pole, single-throw (SPST) switch is in the open position and 120VAC is applied, the reading across the switch with a multimeter will show 120 VAC. This is because, in the open position, the circuit is incomplete, and no current flows through the switch. However, voltage is still present across the terminals because the power source is connected.

In this scenario, the multimeter measures the potential difference between the terminals of the switch. Since one terminal is connected to the live (hot) 120VAC supply and the other terminal is effectively at ground potential due to the open circuit, the voltage across the switch remains at 120 VAC. This reading reflects the voltage being supplied from the power source, which is standardized at 120 volts for residential wiring in many regions.

Understanding this concept is crucial when working with electrical components, as it illustrates the distinction between open and closed circuits and how voltage is present, even if no current flows in an open situation.