Motor Start Switches

Centrifugal Switch:

• Mechanical service mounted on the rotor operated by motor speed
  
  
• Switch is normally closed, connected in series with the start winding
  
  

Current Relay:

• Electrical device used to sense motor current draw
  
  
• Current draw on the run winding is sensed by a coil of larger diameter wire with few turns, magnetic field is created in the coil when current increases to coil pull in current
  
  
• Coil is connected in series with the run winding
  
  
• Switch is normally open and connected in series with the start winding
  
  
• Relay is position sensitive
  
  

Potential Relay:

• Electrical device to sense back EMF induced in the start windings
  
  
• Back EMF induced in the start winding is sensed by a coil of small diameter wire with many turns, magnetic field is created in the coil when the voltage increases to coil pull in voltage
  
  
• Coil is connected in parallel with the start winding
  
  
• Switch is normally closed, connected in series with the start winding, and or the start capacitor
  
  

Solid State Relay:

• Utilizes solid state PTCR technology (positive temperature co-efficient resistor)
  
  
• Application range from 1/8 to ½ Hp
  
  
• Non positional
  
  
• Required cool down period