What is the function of a phase rotation tester?

• A. Measure the magnitude of voltage in a single-phase circuit
• B. Identify the phase sequence of a two-phase system
• C. Measure the direction of a rotating electrical field in a three phase circuit
• D. Detect insulation resistance

Answer: (C)

In a three-phase system, the direction of the rotating magnetic field inside a motor is dictated by the order in which the three phase voltages reach their peaks. A phase rotation tester is used to quickly determine that order, so you know which way the motor would rotate if you connected it to the supply.

The tester connects to the three supply lines and indicates the phase sequence (which phase leads the others). If the sequence is arranged one way, the motor will spin in one direction; reversing the sequence (or swapping two leads) makes it spin in the opposite direction. This is why the test is essential before starting or wiring a motor—to ensure it runs the desired way.

This tool isn’t meant to measure voltage magnitude or test insulation resistance, so those functions aren’t its purpose.