Shield conductivity and proper termination of that shield are the two critical factors in protection from ESD. Shielded jacketed cables from 3M use low resistance copper shields for maximum protection. This chart shows the variations observed while evaluating different termination techniques. Clearly the best shielding is achieved when clamping the shield directly to the metal cabinet, but this is not a practical solution in an I/O application where the cable may need to be disconnected during installation or maintenance. Using a drain wire ground induces a voltage 26 times that of the clamped shield. A compromise between shielding conductivity and usability is a terminated connector in an assembly such as a back shell with jack screws.