In order to improve the network reliability of installations subject to surge events, Cisco offers the CAB-SS-SURGE surge protection cable for Smart Serial interfaces. If a surge event (Lightning/ESD) is coupled onto the cables that interface with the serial card, energy can couple into the transceivers on the front end of the card. The addition of a passive cable assembly (with internal clamping circuitry) can prevent this energy from damaging the transceivers on the front end of the interface. When a voltage over the normal operating levels seen in the serial communication are present on the front end of the interface they are clamped to ground.