Oklahoma Electrical Practice Exam

How is the total line current calculated in a balanced 3 phase system?

1. By total voltage divided by resistance

2. By multiplying phase current by the number of phases

3. By summing all the phase currents

4. By multiplying line voltage with the load

The correct answer is: By multiplying phase current by the number of phases

In a balanced three-phase system, the total line current can be effectively calculated by multiplying the phase current by the number of phases. This is because, in a balanced system, all three phases carry the same current. When there are three identical loads connected in a star or delta configuration, the phase current is uniform across all three phases. Therefore, to determine the total line current flowing through the conductors, you simply multiply the current of one phase by the number of phases, which is three. In practice, this calculation helps to understand the demand on the power supply and ensures that wiring and protection devices are correctly specified to handle the expected current in the system.