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Why is grounding of shield for the ethernet connector important ?

Discussion in 'Electronic Basics' started by aman, Aug 26, 2005.

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  1. aman

    aman Guest

    The Ethernet connectors have two metal pins which act as shield tabs
    which need to be connected to local ground. Can anybody point out as to
    how connecting the metal shield to local ground reduce interference.
    Ethernet CAT5 connector uses differential transmit and recieve. So how
    does grounding of the shield help ?

    -Aman
     
  2. DBLEXPOSURE

    DBLEXPOSURE Guest

    Grounding the shield of a "shielded cat5",(most cat5 wiring is not
    shielded), helps take any unwanted RF energy from outside sources to ground.
    CAT5 and it's twisted pairs and differential data signal are less
    susceptible to this than normal non twisted pair wiring,(Common Mode
    rejection), but still in environments where there is allot of electrical
    noise or RF in the air, shielded wire is sometimes used.

    Also, in some applications, the shielding is used to keep the RF energy
    generated by the network traffic from radiating outside the cable and
    interfering with other equipment such as communications gear.
     
  3. aman

    aman Guest

    I dont understand the idea how connecting the shield to local ground
    reduces noise. The way i think of it is that the CAT5 has differential
    data signals. So it should not care about any ground. I mean how does
    the local ground come into picture. The local ground can be at any
    random potential.
     
  4. aman

    aman Guest

    I dont understand the idea how connecting the shield to local ground
    reduces noise. The way i think of it is that the CAT5 has differential
    data signals. So it should not care about any ground. I mean how does
    the local ground come into picture. The local ground can be at any
    random potential. Please correct me if I am wrong.
     
  5. DBLEXPOSURE

    DBLEXPOSURE Guest

    Hasn't this already been answered?

    The shield on a shielded cat5 is general connected the chassis ground which
    is typically earth ground. Not a voltage reference for your signal but a
    shield to reduce induced noise on the line or reduce radiated rf from the
    network itself.

    Cat5 with it's twisted pairs and differential signals is not terribly
    susceptible to induced interference but in extreme environments it is still
    used.

    With network traffic running at 100Mhz or a gigabit unwanted radiation from
    the network lines can cause trouble with radio equipment. A grounded shield
    can help reduce this radiation..
     
  6. aman

    aman Guest

    So you mean I need to connect the CAT5 connector shield to the AC
    ground (Earth) and not the local DC ground. Right ?
     
  7. DBLEXPOSURE

    DBLEXPOSURE Guest

    You need to use a Cat5 (rj45) plug that is made for shielded wire. This
    will connect the shield to the chassis by means of the connector.

    http://www.weisd.com/store2/GC 30-8994-0000.html
     
  8. aman

    aman Guest

    Gotchas

    Thanks for all your help.
     
  9. Jasen Betts

    Jasen Betts Guest

    yeah, well, to the case of the device, which amounts to the same thing in
    most instances - some devices aren't connected to AC ground.

    Bye.
    Jasen
     
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