You may have mis-wired the motor, perhaps connecting a phase connection to a neutral connection on one leg of a wye connection. If the motor doesnt rotate in two-phase operation, find the reason for phase loss and eliminate it. Restart the motor after shutting down. In simple terms, the current is being alternated during a different time. Three-phase electric motors use three different electric legs with a 1/3-cycle lag between them. The stator and rotor rubs with each other. Star/Delta motor starter troubleshooting. Since this is a motor starter, not a contactor, it sounds like you probably need to rewire so that one side of the pressure switch contacts act as a series STOP switch ahead of the sealing contacts. Check Red to Blue, Blue to Yellow, and Red to Yellow phases. This type of starter circuit uses an autotransformer to apply reduced voltage across the windings of the motor during startup. This is accomplished due to the fact that each one of the three phases has a different offset. An open phase will cause the motor to hum. 3) An electrical possibility is that the motor has an open phase. The best way to know for sure is check the voltage at the motor on all three legs. The most common use of three-phase power is for motors. The three-phase current is unbalanced. The motor's starter wires directly to the motor's wire terminals. I can think of several possible reasons. Three Phase Motor Connection Schematic, Power and Control Wiring Installation Diagrams. Autotransformer 3-phase starter. Most of the motor starter mfrs will publish diagrams on the 4 contactor arrangement, do an image search for "Closed Transition Star Delta Diagram". Single phasing presents a difficult problem if its motor starter doesnt have a single-phase protection feature. Many people aren't comfortable doing their own 3 phase power troubleshooting and repair because they aren't familiar with how they work. Motor hums but 1 Fuse blown in main panel if 1 Check and replace fuse in main panel. That way you can rule out the starter and all the conductors to the motor. Jump to Latest Follow We have had 3 phase motors with similar problems intermittently and turned out to be a weak breaker. To use three-phase electricity, a motor needs windings spaced 120 degrees apart. Verify the motor phases have continuity from phase to phase for all combinations using a multimeter from the motor starter. Three Phase Motor Connection STAR/DELTA Without Timer Power & Control Diagrams Check the reason for the unbalanced three-phase power supply, if it is caused by the power voltage or the motor itself. It is very efficient and carries a balanced power load. troubleshooting the magnetic starter problem possible cause solution compressor wont run 1. Star-Delta (Y-) 3-phase Motor Starting Method by Automatic star-delta starter with Timer. 3. Figure 3 shows the autotransformer three-phase starter circuit. A three-phase motor's large size and high starting torque usually limit its use to industrial settings. This is known as single phasing. 3 phase power is an electrical power system that uses three wires. It would not be unusual for a motor to single phase itself to death from a blown fuse, especially if the thermals were not correct. It provides a unique feature which is a rotating field in order to rotate the motor without the need of a starter circuit. If the loss of one phase occurs before the motor attempts to start, the motor will be in a locked rotor condition, but the amperage will be far less than if all phases were in the circuit. 'S wire terminals carries a balanced power load a phase connection to a neutral connection on leg. 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