Why is grounding of shield for the ethernet connector important ?

[aman]

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

 

[DBLEXPOSURE]

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

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.

 

[aman]

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.

 

[aman]

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.

 

[DBLEXPOSURE]

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.

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..

 

[aman]

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

 

[DBLEXPOSURE]

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

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

 

[aman]

Gotchas

Thanks for all your help.

 

[Jasen Betts]

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

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