What are the two possible sequences for phase arrangements?

The correct answer identifies the two possible sequences for phase arrangements as 1-2-3 and 3-2-1. In electrical systems, particularly in three-phase systems, the arrangement of phases can significantly affect the operation and balance of the system.

The sequence 1-2-3 represents the standard phase rotation, where each phase is spaced 120 degrees apart, promoting efficient power delivery and ensuring that motors run in the intended direction. The alternative sequence, 3-2-1, changes the order of the phases and can lead to different operational characteristics. This variation can be important in scenarios where phase rotation is critical, such as starting three-phase motors, where incorrect phase sequence can result in reverse rotation or failure to start.

In contrast, the other options do not accurately represent valid phase sequences recognized in standard practice. They either contain non-standard numberings or combinations that do not apply to phase arrangements. Understanding the importance of these specific arrangements is crucial for linemen to ensure safety and proper functionality in electrical systems.