What does a voltage drop across a switch indicate?

A voltage drop across a switch indicates that there is an interruption in the electrical circuit, which occurs when the switch is open. When the switch is in the open position, it prevents current from flowing through it, resulting in a measurable voltage difference across the terminals of the switch. This voltage drop is indicative of the switch being off and confirms that there is no complete path for current to travel.

In contrast, when a switch is functional and closed, there would typically be little to no voltage drop across it, as it allows current to flow freely. A shorted switch would create a near-zero voltage drop due to low resistance. Lastly, if the switch were grounded, you would expect to see a different behavior in the voltage readings, likely indicating that the switch incurred a fault rather than simply being open. Therefore, a voltage drop clearly signals that the switch is in an open state.