Oklahoma Electrical Practice Exam

What is the voltage to ground on the "A" phase of a 240v, 3 phase, 4 wire system?

1. 240 volts

2. 120 volts

3. 60 volts

4. 0 volts

The correct answer is: 120 volts

In a 240V three-phase, four-wire system, the voltage to ground on any phase can be determined by understanding the configuration of the system. In this type of system, each phase typically has a voltage of 240V between conductors. However, since it's a four-wire system, it includes a neutral wire. For a balanced three-phase system, the phases are arranged such that the voltage to ground (or neutral) from each phase is typically one-third of the voltage between any two phases. In this case, with a 240V phase-to-phase voltage, the voltage to neutral (or ground) from any single phase, such as the "A" phase, would be 120V. This is because the neutral wire is at ground potential, and the phase voltages are referenced to the neutral. Therefore, in this scenario, the voltage to ground on the "A" phase would indeed be 120 volts. This understanding is fundamental in electrical systems, especially for safety measures and proper circuit design.