Shielding and Bonding as per IEC 61000, Electromagnetic Compatibility (EMC), Installation and mitigation guidelines, Earthing, Grounding and Cabling.
Whether it is a requirement concerning “SAFETY” or a requirement concerning EMC it is required to shunt the unwanted power frequency and high frequency currents and lower the potential difference between two points, the design of the grounding system is same for
Each one of these considerations play a vital role on the Shielding and Bonding Design:
For frequencies above 10MHZ which involves generation or processing or being affected by outside environment, round cables are not effective as bonding straps. Because at high frequencies a round conductor has higher impedance than a flat conductor with the same material cross section.
a) One objection to a meshed earthing network is that this approach results in Earth loops which is undesirable because of noise problems. But a perceived need for separating earthing network because of noise problem should never lead to adopting unsafe practices.
b) The loop between the two chassis mitigates the earth loop problem
When a Shielded cable runs through a metallic wall of an apparatus enclosure or a cabinet, the shield should be connected over its full perimeter to the wall
a) Preferably by an appropriate gland (G).
b) A shield should never run through a wall without electrical contact
c) A pigtail connection is not recommended, not even as a short straight wire because of the high local Transfer Impedance (Zt); some part of the Common Mode Current will pass through the wall due to the pigtail connection.