Why is grounding of shield for the ethernet connector important ?

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.

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.

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.

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

Gotchas

Thanks for all your help.

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..

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.

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