When referring to an electrical circuit diagram, what point is considered to be at zero voltage?

• A. The circuit breaker
• B. The ground reference
• C. The switch
• D. The neutral point

Answer: (B)

Voltage is a relative quantity defined with respect to a reference point. In circuit diagrams, that reference point is the ground node, which is defined as 0 volts. Ground provides a common return path and a stable reference, often tied to earth for safety. All other node voltages are described as how far above or below this point they are. The circuit breaker and the switch are protective/control devices and don’t establish the zero-volt reference. The neutral conductor is a return path for current and, while it can be close to earth potential, it isn’t guaranteed to be exactly zero volts under load. So the point that sits at zero voltage on the diagram is the ground reference.