A: In a motor circuit with start capacitors built-in, you generally only have the capacitors in the circuit for a very brief period of time while the motor's coming up to speed. Once the motor comes up to speed, the capacitor is no longer needed to generate the rotational torque to get the motor spinning. There will usually be a centrifugal switch or a voltage sensing relay to pull the start capacitor out of the circuit.
With AC current, you have a voltage that is varying in time from positive to negative 50 or 60 times per second (50 Hz or 60 Hz). Ideally, the start capacitor should be pulled out of the circuit when the voltage is at "0," but this can't be controlled. If this occurs at any point other than 0 voltage, that charge could be potentially stored in your start capacitor as DC voltage. This could make the capacitor potentially dangerous to handle. Using a bleed down resistor discharges the energy stored in the start capacitor.
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