Chapter 21 Electrical Test and Measurement Equipment 415 Goodheart-Willcox Publisher Figure 21-28. A phase sequence and motor rotation tester is a relatively simple and valuable testing device. An AFG is capable of producing many diff erent wave- forms, including operator-specifi ed waveforms. For example, you can save an oscilloscope waveform as a data fi le, load it into the AFG software, and output the waveform. An AFG is also capable of outputting digital signals and bit patterns. 21.3.11 Phase Sequence Tester When connecting three-phase power to most equipment, especially electric motors, the three-phase conductors must be in the correct relationship to each other. If you were to label each phase A, B, and C, respectively, phase B would start 120° after phase A starts, phase C would start 120° after phase B starts, and phase A would start once again 120° after phase C starts. Th is phase relationship ensures all the phases are in the correct sequence. Note that each phase is 120° apart from the others. If a three-phase motor is connected with all phases in the correct sequence, the motor rotates clockwise as viewed from the shaft end. If any one of the phases is out of sequence, the motor rotates counterclockwise. Th e phase sequence can be corrected by switching any two of the three phase conductors. According to convention, phase conductors should be labeled L1, L2, and L3. Th e motor connections should be labeled T1, T2, and T3. Unfortunately, these conductors are often unlabeled or mislabeled. Th is situa- tion can be corrected using the process of elimination by connecting the motor and seeing which direction it turns when energized. If the motor runs backward, reversing any two phases will correct the situation. A phase sequence tester can be used to label or verify the labeling of the phase conductors. A typical phase sequence tester, Figure 21-28, has three inputs, three voltage-present Copyright Goodheart-Willcox Co., Inc.