Phase Sequence Indicator

Author: E.E. Kimberly

The direction of rotation of a polyphase motor depends on the phase sequence of the voltage supply to which it is connected. It is sometimes necessary to know in advance the phase sequence of the power supply before the motor is started because reversed rotation might damage the load which the motor is to drive. Fig. 9-10 shows a wye-connected network which will indicate phase sequence. Resistors R₁ and R₂ are small neon-filled glow lamps described in Chapter 27. If lamp R₁ glows when the network is connected to the three-phase power lines 1, 2, and 3, the phase sequence is 3-2-1. If lamp R₂ glows, the phase sequence is 1-2-3.

Fig. 9-10. Circuit for Phase Sequence W Indicator