Shield topology and interference control

It is postulated that a closed, perfectly-conducting shield is the only effective means of completely isolating a region from external electromagnetic influences. A very important aspect of interference control is, therefore, tracing of shield topology and identification of all compromises of the closed shield surface. Effective measures for controlling interference are really means of closing the shield protecting the victim circuit. Thus, the use of circumferential bonding of cable shields, and even surge limiter and filter designs, are shield-closing techniques. For the same reason, grounding conductors should not penetrate shield surfaces. Sufficient shield-closing techniques should be applied to reduce interference of external origin to well below the level of interference generated inside the protected space by internal sources.