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Ten Most-Important EMC Problems/Issues and How to Correct Them:
2. Bad Cable Grounding and Improving Electrical Connector Immunity



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Bad Cable Grounding


Above: A cable shield clamp is a much better choice than pigtail ground.

Poor cables and cable design very often lead to RF immunity issues.

Solution: Circumferential (360 degrees) are optimum; Shield “pigtails” are poor.

Divert current back to the shielded enclosure.

• Proper termination of the cable shield back to the enclosure is paramount.

Use high-impedance ferrite chokes to block current.

Connector penetrates through shield: another example of poor EM (electromagnetic) immunity


Above: Module tested for EMC is found to be: unshielded, main connector ground shells has no connection with mate, connectors penetrate enclosure. May be improved like here...


Above: Some improvement: Module halves copper-plated, finger stock added to connectors and ribbed main connector ground shell connects with mate.

An Ideal Cable-Grounding Strategy


Above: A very suitable I/O connector: (top arrow) Note the design incorporates an integrated grounding connection, that solidly connects shielded enclosure with connector ground shell in multiple locations. (bottom arrow) Connector ground shell connected to cable shield.

Ideal cable grounding design – cable shield connected properly to metal enclosure.

Improved Cable/Connector Grounding Strategy


Above: Bottom image shows metal “shim” with “fingers” inserted to shunt internal noise currents.

       
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Updated: Friday, 2007-09-28 1:15 PST