jbcapacitors blog

Start capacitors above 20 microfarads (µF) are always non-polarized Aluminum Electrolyic Capacitors with non solid electrolyte and therefore they are only applicable for the short motor starting time.

Start capacitors briefly increase motor starting torque and allow a motor to be cycled on and off rapidly. Start capacitors have ratings above 70 microfarads (µF), with four major voltage classifications: 125 V, 165V, 250 V, and 330 V. A start capacitor stays in the circuit long enough to rapidly bring the motor to 3/4 of full speed and is then taken out of the circuit, such as by a centrifugal switch that releases at that speed. The motor after that runs more efficiently with a run capacitor.

http://www.jbcapacitors.com/Plastic-Film-Capacitors/JFS-Motor-Capacitor.html