Can you perform a continuity test on a 3 phase motor?

Answer

It is possible to perform a continuity test on a 3 phase motor, although it is slightly more labor intensive than for a single-phase motor. For the 3 phase motor a person needs to check both the phase to ground and each phase to phase aspect using a continuity tester, a multimeter or a megger.

Performing a continuity test on a 3 phase motor has 3 steps:

  1. Begin by connecting a cable and measure across the cable ends using a tool of choice.
  2. Perform a phase to ground test by locating the ground screw on the motor. This should typically be a green hex head screw.
  3. If the ground test shows a proper ohm resistance, then test each phase of the motor in the following order: Phase 1 to Phase 2; Phase 1 to Phase 3; Phase 2 to Phase 3.

Each phase winding should be the same length, meaning that there should be limited discrepancy between the measurements of each phase. They should all be in the high Megaohm range with only approximately 5 percent difference. If there is significant change between any of the phases, then there is an issue with the wiring of the motor that needs to be addressed before it is used.

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