On an energized , intact circuit you will read voltage across an OPEN switch not across a CLOSED switch when testing with a voltmeter.
Both sides of a closed switch are electrically identical (or at least very close) and therefore there should be no movement of electrons between the leads of your voltmeter.
I have seen many new apprentices get confused when they measure across the points of an energized (closed) contactor or between two energized low voltage circuits and they measure 0 volts.
Voltage measurement is always a measurement of potential difference between two points not simply a measurement of how much “Electricity” can be measured at one point.
Across a closed switch = 0 volts (or if it does display voltage it is the voltage drop across the switch)
Across an open switch = applied voltage
Bryan Orr is a lifelong learner, proud technician and advocate for the HVAC/R Trade