What does a phase sequence indicator primarily test?

A phase sequence indicator is a tool used to determine the order of the phases in a three-phase electrical system. This is essential for ensuring that motors and other three-phase equipment operate in the correct direction. When the phase sequence is incorrect, it can lead to motors running in the reverse direction, which may cause mechanical damage or operational failures.

By checking the phase sequence, the indicator confirms whether the phases are connected in the correct order, which directly correlates to the direction of rotation of three-phase motors. This capability is crucial for maintenance and installation work involving three-phase systems, as it helps prevent potential issues that arise from improper phase connections.

The other choices, while they relate to different electrical characteristics, do not pertain to the primary function of a phase sequence indicator. For instance, monitoring voltage levels, current flow, or resistance values serves different purposes in electrical diagnostics and maintenance, but does not address the critical aspect of phase order and its impact on motor operation.