methods and apparatus for protecting data bus ports and their corresponding phy devices from taking damage associated with excess voltage across one or more signal pairs during an intermittent connection . such connections cause the signal pins to carry external device current which raises the signal voltage above the power rails , exceeding the phy device ratings and causing phy degradation or destruction . in an exemplary embodiment , an rc circuit is used to detect the voltage level across a signal pair . if this voltage level exceeds a certain preset voltage level , power to the outgoing serial bus port is shut off and return power is abated . while the circuit is responding , the exemplary embodiment uses a 3 . 6v zener diode to bleed excess voltage to ground . a current monitor / limiter is also used for limiting current if the voltage level detected exceeds a certain threshold .