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Shield of RJ45 (Ethernet connector) right connection

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noisepic

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When design RJ45, they having pin for shielding. I look for some design they connect to some of variations:
1. Inductor to GND.
2. resistor 1M // cap 100nF to GND
3. 0hm // cap 100nF to GND
4. 100nF cap only.
5. Connect to GND.

Which connection is correct? and why?
 

noisepic said:
5. Connect to GND.
Click to expand...

This one in particular do not sound safe, once any artifact noise would be tied to the logic circuitry reference which should be isolated from the field.
 

The reason for the confusion is that it is normally specified that the shield should be connected to GND in both ends, but that is a bad thing in many cases.
One advantage with TP ethernet is that there is a galvanic isolation between the units. This isolation is destroyed if shields are connected to GND in both ends.
The risk is high for unwanted currents in the shield.
Different designers try to solve this problem in different ways.

If allowed, use unshielded connectors in your design! Shielded cables will work anyway, and the shield will help a lot even if it isn't connected to anything.
If unshielded isn't good enough, use a fiber-optical solution.
 

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