S323L/N Phase Sequence Indicator Application Note


Some of the common fault conditions in three-phase Alternating Current (AC) systems include phase reversal and single phasing, i.e. phase loss. Which can all have detrimental and unsafe consequences. Under reversed or phase loss conditions motors, pumps, blowers, and other equipment may operate in the opposite designed direction or draw excessive current on the remaining two phases, which can quickly overheat the motor windings. Power output would then be greatly affected, and cause costly damages to the equipment. Therefore, not only it is crucial to monitor for any phase loss in an electrical supply system, but also important to match the phase sequence rotary direction of the generator and the induction motor.


Attempting to connect a three-phase supply system to a three-phase induction motor, however, the phase sequence of the supply system is unknown.


The Eaglotest S323L/N was developed to provide users with a simple yet safe method to test the rotary direction of 3 phase electrical systems. Simply clamp on to the 3 respective cables (RYB), the instrument will immediately display whether it is a negative phase sequence (Figure 2) or positive phase sequence (Figure 3) system. It does not require the user to remove the insulation layer of the wire, the instrument employs a non-contact method.


In situations where the LED does not flash in a sequential clockwise or counter-clockwise direction, this indicates that a phase is down. Figure 4 shows that the L2 LED light is dimmed, this suggests that the instrument does not detect any electricity in the L2 wire, which then can be inferred that L2’s phase is lost.


  • Easy to use
  • Non-contact
  • Safe – users are not exposed to bare wires
  • Portable
  • Has magnets on the back – allows hands-free operation

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