Understanding AC Motor Basics: Why a 120V Motor Can't be 3-Phase

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SUMMARY

The discussion centers on the limitations of 120V AC motors in relation to three-phase power systems. It is established that while a 120V three-phase motor is theoretically possible, it is not practical due to the absence of standard 120V three-phase power sources. In the United States, the lowest common three-phase voltage is 208 VAC, which translates to 120 VAC line-to-neutral. Additionally, using a Variable Frequency Drive (VFD) can allow a three-phase motor to operate at 120 volts, but this would result in reduced speed to maintain the correct frequency-to-voltage ratio.

PREREQUISITES
  • Understanding of AC motor types and configurations
  • Knowledge of three-phase power systems
  • Familiarity with Variable Frequency Drives (VFDs)
  • Basic electrical voltage and current concepts
NEXT STEPS
  • Research the specifications and applications of 208 VAC three-phase systems
  • Learn about the operation and setup of Variable Frequency Drives (VFDs)
  • Explore the differences between single-phase and three-phase motors
  • Investigate the implications of frequency-to-voltage ratios in motor performance
USEFUL FOR

Electricians, electrical engineering students, and professionals interested in understanding motor configurations and three-phase power systems.

Soleste23
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TL;DR
I have never seen a 120 volt three phase motor.
I have just started my electrician career and I am studying electric motors. why an 120v ac motor can not be 3 phase ? .
 
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Soleste23 said:
Summary: I have never seen a 120 volt three phase motor.

I have just started my electrician career and I am studying electric motors. why an 120v ac motor can not be 3 phase ? .
Are you aware of any 3 phase power sources that are 120 volts leg to leg?
 
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There's no physical reason that a 3-phase motor can't be 120 Volt, but it would require a 3-Phase 120 VAC supply (which is not a standard anywhere that I know of). In the US, the lowest common 3-Phase voltage is 208 VAC - that's 208 VAC L-L and 120 VAC L-N.
 
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1652988611774.png

https://www.plugsocketmuseum.nl/ThreePhaseTransformers.html
 
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Something to think about: A VFD driving a three phase motor would output 120 volts at about half speed in order to keep the frequency to voltage ratio correct.
 
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