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The supplies a reduced impedance return path for currents generated from the switching voltages amongst the primary and secondary windings of the transformer. Without this minimal impedance path, the currents will probably come back by other avenues - typically via stray capacitances from secondary into Live or ground or Neutral - often bypassing the input filter and generating considerably increased quantities of ran EMI."y capacitor" s suppress electrical noise and provide safety against electrical shocks and fires. They reduce devices and machines out of sending and receiving electromagnetic and radio frequency interference. Once attached between line phases (round the line), capacitors efficiently check symmetrical disturbance. "y capacitor" s, on the opposite side, when attached into a line bypass -- which is, between a lineup period and a point of zero possibility -- keep outside asymmetrical disturbance.