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Troubleshooting split-phase (single phase) U.S. Motor  

Split-phase U.S. Motor is often serviced and repaired due to issues with the centrifugal switch, thermal switch, or capacitor. However, depending on the age and power of the motor, it may be time to replace it entirely. The first thing you should do while troubleshooting a split-phase motor is to turn the power to the motor OFF. Once the power is off, you can then determine if the motor is controlled by a thermal switch. 

In this blog post, we’ll walk you through some common troubleshooting procedures for split-phase motors.  
 

1. Check the centrifugal switch, thermal switch, or capacitor  

 
If you are having issues with your single-phase motor, the first thing you should check is the centrifugal switch, thermal switch, or capacitor. These are typically the source of issues with single-phase motors.  

 
2. Service or repair the motor  
If the centrifugal switch, thermal switch, or capacitor is at fault, you may be able to service or repair the motor. However, if the motor is less than 1 HP and older than 10 years, it is typically replaced. The motor is typically always replaced if it has less than 1/8 HP.  

 
3. Replace the motor  
If you need to replace the motor, make sure to get one that is compatible with your system. You will also need to install and wire the new motor correctly.  

 
Thermal switches are designed to automatically turn the motor OFF when it overheats. This prevents damage to the motor and extends its lifespan. Some thermal switches have a manual reset, while others have an automatic reset. If you’re dealing with a thermal switch that has an automatic reset, be aware that the motor can restart at any time. Always exercise caution when working with this type of switch.  


In general, troubleshooting a split-phase motor is relatively simple. By following the steps outlined above, you can quickly and easily determine if there’s an issue with the thermal switch otherwise you should read ahead in detail to resolve the problem.  

  • If your split-phase motor does not start, the first thing you should do is check for voltage at the motor terminals. You can do this with a voltmeter. If there is no voltage at the terminals, then the problem may be with your power source. If there is a voltage at the terminals, then the problem may be with the motor itself. In either case, it is best to consult a qualified technician to diagnose and repair the problem.  
  • If the problem is with the motor itself, the first thing you should do is turn the handle of the safety switch or combination starter off. Follow the policy of the company, lock out and tag the starting mechanism. This will prevent anyone from accidentally restarting the motor while you are working on it. The next step is to consult a qualified technician to diagnose and repair the problem. 
  • Connect the Fluke 87V to the same motor terminals from which the incoming power lines were unplugged when the power is off. The starting and running windings’ resistance will be detected by the ohmmeter. Due to the parallel nature of the windings, their combined resistance is lower than the resistance of either winding taken separately. If the ohmmeter reads zero or infinity, the motor should be replaced. The first step is to turn off the power to the motor. The next step is to remove the motor from the equipment it is driving. Once the motor is removed, take it to a qualified technician for diagnosis and repair. It is a point to note that a repair would not be cost-effective due to the motor’s modest size.  
  • In case you find any burning or broken springs, this is a sign that the centrifugal switch needs to be serviced or replaced. If there are no obvious signs of problems, you can check the switch using an ohmmeter. To do this, disconnect the power to the motor and remove the switch from the motor. Once the switch is removed, use the ohmmeter to check for continuity between the terminals. The switch is fine if there is continuity. Otherwise, the switch must be restored.  
  • At last, the switch is operational if there is continuity, it can be manually operated, which should only be carried out by a qualified technician. The first step is to disconnect the power to the motor. Then, remove the motor from the equipment it is driving. Once the motor is removed, take it to a qualified technician for diagnosis and repair. 

Check out Split-phase U.S. motors online at Kpaulindustrial.com (authorized distributor, an SDVOSB) and contact us in case of any query regarding discounts or bulk orders. 

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