shielded cable

[mvbub]

Hi, looking for a standard for installing twisted shielded cable, in particular the termination of ends ie: insulate foil where cable sheath cut away.
I need to convince a contractor of the proper methods of installing.

Any help will be appreciated.

Mvbub

[bennie]

The shield should be grounded but not used for grounding any other equipment.

In otherwords, the shield should be single ended. Electrostatic draining is the purpose of the shield.

The shield connection point should be at the end nearest the ground electrode.
(Drain electrons downhill :p )

[dereckbc]

Shields should be terminated on one end only at the terminal equipment end.

[mvbub]

Thanks, all that is understood but this is a modbus installation and the contractor did not insulate the foil from around where the outer sheath was removed and all in all a very sloppy installation.
I was hoping to find a testing authority, or a manufacture standard for installation method to document requiring him to correct the installation other than a neat and workman like manner.

Again any help would be appreciated.

[bennie]

Search the Modbus websites. There is 39,600 pages.

[tom baker]

Here is how I terminate a STP cable, if it has a drain wire: Trim off 6" of the cable jacket. use a 1" length of heat shrink and a 6" length of clear sleeving. slide the clear sleeving over the drain wire, slide the heat shrink over the cable, center it over the end of the STP jacket, and shrink. strip off the clear sleeving just like a conductor.
the drain wire or sheild is bonded at one end only.
If its braided shield, its a bit tricker, you have to pull the conductors thru the shield, and then use clear heat shrink over the shield, and then heat shrink over the end of the cable jacket

[iwire]

Tom that certainly sounds like a very clean and neat installation. :)

The only place I regularly deal with a drain wire is for some fire alarm systems addressable loop.

For this all we do is twist the shield from the incoming cable to the shield of the out going cable. Then back wrap that around both cables and tape them thoroughly to prevent contact with grounds.

Some of the fire alarm devices have wanted the shield terminated on each address module, for that we do it more like Tom's method, although we use a piece of insulation stripped from a 12 awg in place of the clear tubing, and tape in place of shrink wrap.

Although both ways accomplish the same thing, Tom's method obviously results in a more professional looking installation. :)

[mvbub]

Thanks, Tom's method is how I like to see it done.
Does anyone know of an instruction method I could use for a specificiation? It would give me a stronger argument if I could refer to an official document.

Thanks, again
Mvbub

[bennie]

Tom's instructions appear offical with me. His credentials substantiate his recommendations.

The only other source will be the cable manufacturer. Contact a customer service rep.

Carol or General Cable should have a website.

Search the sites for "STP Cable" also. There is a lot of information for print out.

[ October 12, 2003, 10:13 AM: Message edited by: bennie ]

[dereckbc]

Tom you must have done some work in the Telecom industry. That is precisely the method we use. Aside from manufacture procedures the only other source of info would come from BICSI.

[hbiss]

...insulate foil where cable sheath cut away

The foil should be removed along with the jacket (sheath) at the point it is stripped leaving the conductors and the drain wire. No reason to insulate it because there shouldn't be any foil hanging out to begin with. Just go back and remove it. Just knick it with cutters, scissors or a knife where the jacket ends and tear it off.

The foil is in continuity with the drain wire and that, as well as the end of the cable can be covered with sleeving and shrink tubing overall as Tom suggests. Makes for a nice neat job but is not absolutely necessary. We'll do that in frames or racks but other places it sometimes is difficult to use a heat gun or sheer volume makes it impractical.

[tom baker]

Thanks for the comments on my method. It does look neat, but is time consuming. I insulate the drain wire as the terminations I make are in cabinets and the bare drain wire could make contact with an adjacent terminal.
I didn't mention but I also label the STP cable and each individual wire with a shrink on wire marker.

[mvbub]

Thanks to all for the information, the reason for this was I had an application of 16 units on a modbus scanner. The electrical contractor on site had attached the stp without insulating cable ends where sheath cut away or drain. In some cases drain wire was 4" long adjacent to 110 volt ac terminals. Using this forum, and other sources I required him to correct installation, while doing so just moving flexible conduit attached to equipment caused a drain wire contacted the 110 volts damaging all 16 modbus inputs at a cost to him in excess of $5,000.
This could have cost the end user after warranty if had not happened just today

Again if anyone can come up with such a simple standard it would help us all in the industry.

Thanks again for all the excellent help!

mvbub

[hbiss]

No need for a standard, just good workmanship, common sense and knowing what you are doing. Like I always said, there are plenty of "hackers" in the LV field. Perhaps the $5K chargeback will help this guy see the error of his ways.

[gwz2]

I am not "UP" on the BICSI but I would think a standard is the way to go. That way every-one should know or can find the information to do the installation the correct way.

The NEC is not an installation guide where a standard could guide the proper way to do the installation.

[jrdsg]

have to agree with hbiss. since as bennie and others indicate the theory here is pretty straight forward, what more could be needed in the way of a standard than "neat and workmanlike manner"?

bicsi, cedia, and other standard-mongers have a love-hate relationship with the trades. be careful what you wish for.