Providing Solutions in centrifugal
Speed Switching for Over 65 years
Motor Switch Selector
Basic Operation

Capacitor start motor require a method to extract speed data from the voltage across the motor start winding. By comparing the start winding RPM-sensitive voltage with the main AC input voltage (which serves as a reference voltage), the switch determines when the start circuit should be energized. The electronic switch interrupts the start circuit current after the motor has accelerated to the cut out speed, and reconnects the start circuit whenever the motor speed has fallen to cut in speed (usually about 50 % of synchronous motor speed).
Unit of Measure


Typical Maximum Motor

N/A 1 hp

Full Load Motor
Current Rating (115 Volts)

N/A 12 A

Full Load Motor
Current Rating (115/230 Volts)

N/A 12/6 A

Switch Rating
Permissible Max
Start Winding Current

N/A 25 A

Start Circuit Voltage

N/A 115 V

Part Number

N/A 4-7-21025-11-UB1 4-7-21025-20-UB1

Typical Cut Out Voltage

N/A 147 V

Typical Cut In Voltage

N/A 37 V

Package Style

N/A 11 20



Additional Features


  • UL E71115 and Canadian UL Recognition (also CSA Certification on 11 package).
  • Operating Temperature: -40 ºC to 65 ºC (-40 ºF to 149 ºF) [for operation between 65 ºC and 85 ºC (149 ºF and 185 ºF), consult factory.]
  • Operating Voltage: 115 VAC SINPAC® Switch 90-130 VAC. For dual voltage motor equipped with center-tapped mam winding: 90-130 VAC or 180-265 VAC.