Many believe that "if equipment is properly shielded" (shield wire plus conduit) you won't have transient problems. Of course, experience shows this not to be true. The reason is that when the EM wave passes the shielded wires, currents are induced into conduit or shield and travels to the best "earth ground" available. The transient currents are then coupled inductively to the inner conductors, which lead directly to unprotected electronic components (See Figure 20).
Figure 20
Another fallacy is the belief that burying the cable in the earth will prevent transient problems. The earth is essentially transparent to a lightning EM wave so very little attenuation is observed.
In shielding then, the principal is to use good shielding on sensitive data lines and ground only one end. Shielding will attenuate RF and help some with lightning. Always ground the shield at the receiving or measurement side, not both ends. When both ends of a shield are grounded, ground currents can flow, conducting noise or creating " ground loops" (See Figure 21).
Figure 21
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