Terminating Shielded Cables for CMM

I do not have much experience with shielded cables and have been hearing many different things, so I was wondering if somneone can answer a few thinsg for me.

We have a tower installation with a CMM2 and 3 AP’s and we have had to do some changes in the wiring which resulted in us having to cut the end off of our cables at the ground level. Everything on the tower end is intact. Since I had to cut the ends off of our wires at the CMM end, I ended up recrimping them using standard non shielded connectors:

1. I was told that if we use shielded cables BUT do not use shielded connectors at each end, then effectively we have negated the whole shielding aspect of the cables. Is this true?

2. What exactly is the proper procedure for using shielded connectors? Where does the bare grounding wire that is in the shielded cables go? I assume that it needs to make contact with the metal jacket on the connectors, but how exacly?

3. On a realted note, if we do not HAVE to use shielded connectors at each end, then is there a way to get around this? Is there a way to connect the grounding wire to something to get the same result as using shielded connectors?

4. Are there special crimpers used for shielded connectors, or will my standard crimper work?

5. And lastly, I have found RJ45 shielded connectors everywhere, but I cannot seem to find RJ11 sheilded connectors. Anyone have a source for these?


Thank you.

well the cable i have used, actually has a drain wire, at the cmm end i have stripped back 18" of the insulation crimp on an end while leavingthe 18" drain wire seperated, that drain then i actually physically ground to a block that is connected to earth ground and tower ground.

MBWtech wrote:
well the cable i have used, actually has a drain wire, at the cmm end i have stripped back 18" of the insulation crimp on an end while leavingthe 18" drain wire seperated, that drain then i actually physically ground to a block that is connected to earth ground and tower ground.


I am sure that works, but the premade cables that we got do not do this, so I believe that the termination and grounding takes place within the plug. Basically it seems that if the CMM is grounded, then the drain happens by contact with the metal jacket on the plug and the metal casing of the ethernet jacks on teh CMM.

Anyway, still have not seen any instructions on this....

The easiest way to ground these boxes is to connect a 12gauge copper wire to the grounding terminal next to the 24V connection. Connect the other end to a electricity meter, or mast. Use a grounding rod if those are unavailable. If a grounding rod is unavailable, ground to electrical conduit. Just make sure the distance between the ground terminal at the CMM and the other end of the ground wire is shorter than the shortest wire connected to the CMM. If lightning does strike an AP, it will ground out without destroying everything connected to the CMM.

This is just a tip coming from my knowledge of certified grounding sources. I used to work for a cable company. They know how to ground, because if they don’t they get sued.

komseh wrote:
The easiest way to ground these boxes is to connect a 12gauge copper wire to the grounding terminal next to the 24V connection. Connect the other end to a electricity meter, or mast. Use a grounding rod if those are unavailable. If a grounding rod is unavailable, ground to electrical conduit. Just make sure the distance between the ground terminal at the CMM and the other end of the ground wire is shorter than the shortest wire connected to the CMM. If lightning does strike an AP, it will ground out without destroying everything connected to the CMM.

This is just a tip coming from my knowledge of certified grounding sources. I used to work for a cable company. They know how to ground, because if they don't they get sued.


Thanks but the question here is not how to ground a CMM. The question is in regards to using shielded wires and shielded connectors and how THEY need to be terminated. Thanks.
http://motorola.canopywireless.com/comm ... 9e30911461
captain kirk wrote:
http://motorola.canopywireless.com/community/viewforum.php?f=1&sid=9db6d93ad8ce63f439be799e30911461


Where is that link supposed to take me to? It just takes me to teh Forum's first page????

The purpose of screened/shielded cable is to intercept radio interference before it gets to your wires and redirect it to the ground through the drain wire, not to protect your equipment from lightening. there is a different procedure for that. The answers to your questions are as follows.

"1. I was told that if we use shielded cables BUT do not use shielded connectors at each end, then effectively we have negated the whole shielding aspect of the cables. Is this true?"

No…there are shielded connectors but even they have to be grounded in some way. this is commonly used in telecommunications rooms that use a grounded patch panel which is attached to a grounded rack that is grounded to a busbar. Unshielded connectors can be used but the drain wire must be grounded in some way such as busbar. Just be sure to expose enough of the drain wire. i recommend the grounding box commonly used with canopy installations. connect the drain wire to the grounding post along with the ground wire that will eventually lead to your grounding post.


"2. What exactly is the proper procedure for using shielded connectors? Where does the bare grounding wire that is in the shielded cables go? I assume that it needs to make contact with the metal jacket on the connectors, but how exacly?"

The steps are on this link.

http://www.belden.com/college/college.htm

3. On a realted note, if we do not HAVE to use shielded connectors at each end, then is there a way to get around this? Is there a way to connect the grounding wire to something to get the same result as using shielded connectors?

depending on your location a grounding rod, busbar or something else you are sure is grounded will be needed.

"4. Are there special crimpers used for shielded connectors, or will my standard crimper work? "

your standard crimper will work.

“5. And lastly, I have found RJ45 shielded connectors everywhere, but I cannot seem to find RJ11 sheilded connectors. Anyone have a source for these?”

Sorry, can’t help you there. :frowning:

tihs link should direct you to the correct tutorial for terminating shielded/screened.

http://bwcecom.belden.com/college/colle … ll&P6=null

Thank you everyone. I think I have gotten some good information here.

let me know if you need more info

captain kirk wrote:
let me know if you need more info


Well, one thing that does not make total sense to me is that based on your description above, I should leave a length of the drain wire exposed and tied into some sort of grounding busbar or other device such as the canopy surge protector's grounding nut. But that goes against the instruction for properly terminating a shielded connector, and also I find in interesting that Motorola does not discuss any such need at all. Sure, the surge is supposed to be grounded and the CMM in grounded, and they always talk about using shielded cables, but they never talk about this method of grounding the shielded cables themselves. They always gave me the impression that if the CMM is grounded, then the shielded cables will be grounded as long you use shielded connectors that have the metal jacket on them. I assumed that this was accomplished because the metal jacket makes contact with the housing around the Ethernet jacks on the CMM. Is this not correct? So you are saying that as someone else mentioned above, that we should have a long length of the drain wire exposed and tied into a separate ground of some sort?

Thanks.

I’m assuming your using shielded cable to protect against rf interference and not lightening. you CAN either use shield connectors but they only act as a chanel from the drainwire to the grounded device. In other cases you can mount the drain wire to an appropriate device such as a patch panel with mounting screws supplied in the setup tho usually those are in a telecommunications room.

If you are in a field and not in an ideal situation then you will have to make other arrangements and i think we are all delving into new territory. Using the motorolla grounding module to complete your rf shielding I am unsure of. I’ve printed this pdf but have not read it myself. here is the link. let me know what conclusions you come to and i promise to read them asap.

http://www.canopywireless.com/pub_files … ection.pdf

http://www.canopywireless.com/pub_files … Manual.pdf

btw,even if you don’t have shielded connectors you should follow the directions to make sure that your drain wire is making contact with the foil so you can ground your drain wire.

Please don’t count on the drain wire for lighting protection. it won’t work.

Yes, my main concern is interference and not lightning protection. This is a tower installation (on a very crowded tower).

It is actually rather odd, because we have had this set up for nearly 2 years and it had been running flawlessly, until last December. Suddenly we started getting connection problems and GPS dropped links, etc. (just to 2 of 3 AP’s). I went up to the tower last month and did some clean up work and recrimpped some connections, etc., assuming that we have a bad connection somewhere. At the time I did not have shielded connectors with me, so in the clean up process I had to shorthen and reroute some wires, so I ended up having to recrimp them at the CMM end with regular connectors. Well, things got back to normal for a while, but not quite as good as they were before, so I have been attributing this to the lack of shielded connectors.

But as of 2 weeks ago, one of the AP’s is constantly loosing GPS sync again, which of course brings down all subscriber units as they will not register to it. So looks like we still have a bad connection somewhere. I am assuming that the fault is not with teh CMM, since this mainly happens with only 1 of the 3 AP’s.

So anyway, armed with new shielded RJ-45 and RJ-11’s I’ll be trekking back up to the tower site to redo all connectors, etc. We’ll see if this all makes a difference.

Thank for all the help.

BTW, I was told my a Motorola tech that I do not need to use surge protectors on an installation if the AP’s are going into a CMM which is in turn grounded. Any thoughts on this?

provided there is no equipment failure then possibly something in the environment has changed such as a new broadcast tower.