Get Your Motor Running: Reduced Voltage Starting


This Benshaw white paper explains the principles and benefits of reduced voltage starting for three-phase induction motors. It explores how different motor designs and starting methods affect torque, current, and overall system performance. The guide provides practical examples, data tables, and speed/torque curves to help engineers and maintenance professionals make informed motor and starter selections.

Key Points

  • Understanding Motor Starting: Explains how full voltage (DOL) starting causes high inrush current and how reduced voltage starting mitigates it.
  • Motor Categories (A–D): Outlines four NEMA design types with their typical locked rotor current (LRC) and torque characteristics.
  • Performance Calculations: Demonstrates formulas and data tables to predict torque and current relationships under reduced voltage.
  • Design Optimization: Shows that selecting the right motor design—not just increasing size—can improve performance and reduce costs.
  • Motor Design Impact: Details how rotor and stator design influence starting torque, current, and efficiency.
  • Application Examples: Provides real-world cases comparing torque and current characteristics across different motor designs.
  • Speed/Torque Curves: Illustrates how varying motor designs behave under load and how to match them to machine torque requirements.
  • Global Engineering Insight: Produced by Benshaw, a global leader in applied motor controls and reduced voltage starting solutions.