The charts will enable you to make a side-by-side comparison of the different types of reduced voltage starters.

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Comparing the Reduced Voltage Starters

The charts will enable you to make a side-by-side comparison of the different types of reduced voltage starters.

You may find this information useful as you work with a customer to select the right equipment for his application.

Starter Type	Starting Characteristics			Standard NEMA Motor	Transition Type	Extra Accel Steps Available	Install Cost
Starter Type	Volts at Motor	Line Current	Starting Torque	Standard NEMA Motor	Transition Type	Extra Accel Steps Available	Install Cost
Primary Resistor	65%	65%	42$	Yes	Closed	Yes	High
Auto-transformer	80%65%50%	62%42%20%	62%42%20%	Yes	Closed	No	High
Part Winding	100%	65%	48%	*	Closed	Yes**	Low
Wye Delta	100%	33%	33%	No	Open***	No	Medium
Solid State	Adjust	Adjust	Adjust	Yes	Closed	Adjust	Highest
* standard dual voltage 230/460 V motor can be used on 460 V systems very uncommon* closed transition available for higher cost

Starter Type	Advantages	Disadvantages	Applications
Primary Resistor	Maximum starting torqueSmooth accelerationHigh power factor during startUp to 5 acceleration points available	Low torque efficiency Resistors generate heat Long starts require expensive resistors Difficult to change starting torques under varying conditions	Belt and gear drives Conveyors Textile machines
Auto-transformer	Highest torque per ampThree starting torques available through tapsGood for slow startsMotor current exceeds line current at start	Most expensive at lower HP designs Low power factor Large physical size Distinct switching transitions during tap changes	Blowers Pumps Compressors Conveyors
Part Winding	Least expensive methodStarts most dual voltage motorsSmall physical sizeOnly two half-size contactors are requiredTypically limits motor torque and current to 50% of normal at start-up	Bad for slow starts and high inertia loads due to poor starting torque Special motor required over 230 V Requires a 9-lead wye or a 6-lead delta winding Offers only a single step Motor will overheat if first acceleration step exceeds 5 seconds	Reciprocating compressors Pumps Blowers Fans
Wye Delta	Good for slow starts and high inertia loadsHigh torque efficiencyEliminates the resistor and autotransformer losses at start-upGood for stringent inrush restrictionsGood for frequent startsIn widespread use in Europe	Requires special wye-delta motor Low starting torque may not be able to start heavy loads Momentary inrush during open transition period	Centrifugal compressors Centrifuges
Solid State	Energy-saving features availableRugged and reliable with no moving parts at allSoft startsAdjustable acceleration timeCapable of rapidly switching heavy currentsUsually self-calibratingAdjustable braking	High cost Specialized installation and maintenance Electrical transients can damage unit Requires good ventilation, and supplemental cooling in some environments May need to be oversized for high-inertia loads May create noise and/or harmonics	Machine tools Hoists Packaging equipment Conveyor systems