A switch protection circuit includes a discharging circuit and, optionally, a clamping circuit. The discharge circuit operates prior to the switch completing the switching action to discharge capacitance from a signal line of a cable connected to a device under test to a ground voltage. When not discharging, the discharge circuit presents low leakage to a measurement circuit so as not to interfere with such measurement. If present, the clamping circuit clamps a signal line of the cable to a guard structure of the cable so that the discharge circuit can couple both the signal line and the guard structure to ground. The protection circuit operates without significantly worsening low current performance of the measurement instrument.