If B phase lags A phase by 120°, how much does C phase lag A phase?

In a three-phase system, the phases are typically separated by equal angles. When one phase lags another, the relationship can be determined using the concept of phase angles.

If B phase lags A phase by 120 degrees, this means that the phase order is such that A leads B. In a standard three-phase system, the C phase is usually 120 degrees behind B phase. Since B is already 120 degrees behind A, C phase would be positioned another 120 degrees behind B.

To find the total lag of C phase relative to A phase, we add the two phases of lag: 120 degrees (for B relative to A) plus another 120 degrees (for C relative to B), resulting in a total of 240 degrees. This positions C phase effectively 240 degrees behind A phase in the timing of the cycles.

Thus, the correct answer is that C phase lags A phase by 240 degrees.