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Shielding and Bonding Design

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

  • Personal Safety
  • Lightning
  • EMC & Equipment protection

Each one of these considerations play a vital role on the Shielding and Bonding Design:

  • lightning and personnel safety dictate the design of the earth electrode;
  • safety and installation protection dictate the size for the Grounding conductors;
  • the EMC behaviour requirements determine the layout of the Grounding network.

Misconception of "Dedicated", "Independent" or "Isolated" Earth Electrodes

Shielding Bonding Earth Electrodes

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.

Example of Optimal Bonding of a Shielding Cable to the enclosure by a Compression fitting providing a 360-degree bond

Shielding Bonding Design Cable

Misconception of "Dedicated", "Independent" or "Isolated" Ground Electrodes

Shielding Bonding Signal Cable

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

Penetration of a sheilded Cable through the Wall of a Metal Enclosure

Shielded Bonding Cable Design

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.

Earthing system for a drive with convertor and associated electronics

Grounding System Electrical Electronics

Generator Station Building Ring Earth Electrode

Grounding Bonding Shielding Surge

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