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