The voltage across the contacts energized in line #8 during operation (thermostat closed, fan auto) is:

• A. 0 V
• B. 120 V
• C. 240 V
• D. 480 V

Answer: (A)

When a contact is energized and closed, it becomes a very low-resistance path that simply carries current from one side to the other. Because the two points connected by the closed contact are at nearly the same electrical potential, the voltage drop across that contact is essentially zero. In this thermostat-controlled circuit, line #8’s contact closes to energize the load, but the contact itself behaves like a short taken across the supply path, so you’d measure almost no voltage across it (real-world drops are only a few millivolts due to contact resistance). The full line voltage remains in other parts of the circuit, not across the closed contact itself.