ECN Forum Forums General Topics of the Trade Voice - Data - Video Discussion Shielded Cat 5

I am finishing up a small power plant where shielded Cat 5 cable was specified for network communications between the generator PLC's and the master controller. Shielded cable really isn't necessary but thats what was speced and installed. The system will operate at 10 Base T speed. I have terminated both ends of all the cables with shielded connectors. My question is since both ends required RJ-45 plugs there was no way to take the shield to ground on either end. Does anyone for see any problems with this?

I agree this is not really the intent of the cat 5 standard and the shielding will change the impedance of the cable. At 10mz it should still work fine. I would pigtail and ground the shield at one end only, the end closest to the system grounding electrode, just to keep it from causing problems.

Nick,

"Rip" out enough of the Shield's Drain Conductor from each of the Cables (at the Controller's end), and Bond these guys to an Equipment Grounding Reference.

Insulate the Shields and Drains (wrap with tape, etc.) at the PLCs' ends, so no Shields end up touching Grounded Metal Enclosures, or EGCs.

Scott35

There are shielded RJ45 connectors. I have no idea where to get them--I've only ever seen them on the Cat5 cables that come with cable modems. Basically they have a metal piece which fits over the connector, makes contact with the drain wire, and makes contact with the two ground fingers on each side of the RJ45 jack (if it's a shielded RJ45 jack that is).

I am not familiar with the way that PLC's are wired but if all the wiring goes back to a central location a shielded patch panel will have provisions to terminate and bond the drain wires in the cable you have ran.

Here is one that I have found: http://www.siemon.com/e-catalog/products/HD5_Screened_Patch_Panels.asp

I disagree with Scott 35 on terminating both ends of the drain. In the past this has caused big problems in system work we have done with shielded communication cables operating at high frequency. The problems went away when only one end of the drain was terminated.

Sorry Scott, I misread your post. I thought it said terminate both ends, when in fact you correctly said to terminate "both" the shield and the drain. My apoligies offered.

This Is what I used although it was a different suppler. This is the cable used and exactly how both ends are terminated. I have some slack in the cable so maybe I should go back and cut enough back to get the drain wire out. It is only for terminations. What do ya think??

[Wow, the second link doesn't take you all the way there! Click cable training then installations then RJ-termination guidelines for Belden's shielded category 5 cable.]

[This message has been edited by Nick (edited 05-19-2005).]

What sense does it make to use a plug (especially one for shielded cable) THEN hard wire the drain wire? Anybody really think this was intended to be done this way?

There are shielded jacks that will make contact with the outside of the shielded plug to provide a ground path. If your equipment doesn't incorporate shielded RJ-45 jacks that should be a pretty good indication that shielded cable isn't needed and is going to be pretty tough to use if you do.

If you are bent on doing this what I would do is put regular RJ-45 plugs at the PLC ends. I too recommend that you only connect the shield at one end so cut the foil and drain wire back and forget it.

At the controller end I would terminate the runs on a regular patch panel, not a shielded one. Leave the drain wires long from each run and terminate the pairs in the normal manner. Again trim the foil back flush with the jacket. (The drain wire makes contact with the foil for the length of the cable so don't worry about the foil.)

Now you are going to have all these drain wires, neatly twist them all together and connect them to a ground wire (wirenut is fine) which goes back to the case of the controller or the electrical ground the controller case is connected to. That's it for the grounds.

Now simply use regular patch cords to connect the patch panel jacks to the controller jacks. The length should be so short that shielding is unnecessary.

-Hal

Hal, why would you say to use a regular patch panel instead of a shielded one that has the provisions to terminate the drain's ??