It isn't necessary. Even more so the better your power supply the less you need one.. I have put together a few direct drives and the motors came with matched capacitors but I didn't install them. If you feel like your motor isn't running well, you can install one and see if it works better, but shielding a motor is more for protecting the circuit in a power supply. You see the motor spinning creates a second frequency ( basically noise ) in the return voltage ( headed to ground ). This noise can confuse other circuits used to read CPS and duty cycles on some power supplies and cause them to shut off. Again like a i stated before a good power supply will be shielded from this and the noise will just be fed to ground where it will die. Additional circuits on a common ground rail done correctly will have a diode and a capacitor at the beginning to secure polarity and reduce noise, thus reducing the need for a capacitor on the motor. If you were using something with an audio output on the same common ground I would highly suggest shielding the motor, as you might hear it in the audio.


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