An overvoltage protection apparatus for use with a data transmission interface, having at least one data transmission line associated therewith, for protecting the interface from power spikes, transients, and/or the continuous application of an excessive voltage. In a preferred embodiment, the apparatus includes at least one voltage limiting device associated with each data line. Each voltage limiting device being connected at one end to the associated data line, and at a second end to a current sensing and switching structure, which is in turn connected to ground. The current sensing and switching structure monitors the current through the voltage limiting device. In the event an excessive voltage is applied to a pin or data line of the interface, the voltage limiting device briefly absorbs the excess power and generates an increased current. This increased current is sensed by the current sensing and switching structure, which responds by opening a switch which disconnects the interface from ground. The current sensing and switching structure automatically reconnects the switch after a preselected time period. The switching structure continues to monitor the current from the voltage limiting device, and open and close the switch, for an indefinite period of time until the excessive voltage condition is removed.