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Standard Practice for Voice over Cat5

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14 replies

by mikey.g.0727

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Hi - When running voice over Cat5, should you typically run 1 phone line per Cat5, or multiple lines per cable?

If one line per cable, what is the proper thing to do with the un-used pairs on the telephone block in the closet?

If multiple lines per cable, what is the best way to break out the lines on teh users side to connect to telephones in a neat way?

Thanks -

14 replies

by maniacman

I'm no telecomm expert, but all the VoIP installs I've seen to date all used Cat5e or Cat6 twisted pair cable because it can sustain gigabit speeds without signal degradation.

by mikey.g.0727

Hi - You are right, Cat5e at a minimum, I should have specified, I was being general. I am not talking voip though, just analog / pbx telephone lines.

by michael kassner

Just to make sure, are you going to run VoIP over the Cat5/6, or are you referring to normal PBX digital lines or even analog lines over Cat5/6?

VoIP requires the normal two twisted pairs per line, where as PBX digital and analog require a single pair per line. So with a typical Cat5/6 cable you could run 1 VoIP line or 4 PBX digital and analog lines.

I better qualify that statement slightly, I have on occasion been required to run two Ethernet/VoIP circuits on one Cat5/6 cable, but do not recommend it as there is an elevated potential for cross-talk.

by mikey.g.0727

Hi - Yes, I am not talking Voip here, Just analog / Pbx voice lines. It was really more a general question of how to terminate it at the closet / station, if you are running 4 lines per cable vs 1 line.
Thanks

by michael kassner

If that is the case, then you really do not even need to run Cat5/6. Cat3 will be sufficient and you can run 4 pairs through the typical cable.

If the extra cost is not an issue, I generally prefer to use Cat5/6 though, just as a proactive thing.

by mikey.g.0727

I was going to use all CAT5e just for the sake of dealing with only one cable type. My real problem is, I havent run voice before, I am not sure about how it gets terminated at the closet? Do you typically run voice to a patch panel? Right to a 100 / 66 Block? Or something else?

Thanks

by michael kassner

When running voice over Cat5, should you typically run 1 phone line per Cat5, or multiple lines per cable?
..That is up to you, up to 4 pairs/lines can be run over one Cat5 cable. I typically use as many pairs as possible on each cable to save money. I think we need to describe a simple telco setup in a bit more detail. I hope this may help explain.

PBX
|
>-PBX 66 cross connect
??...|
??...>- Backbone run to remote location
??.???.|
??.???.>-Remote 66 cross connect
???????..|
????????>- Individual phone trunk lines

The 66 cross connect is a punch down block that allows you to easily connect all of the pairs coming from two different sources and interconnect them.

The backbone run can be anything from a Cat5 cable with 4 pairs or a special telco cable with up to 50 pairs (I think). That type of cable is used to run multiple lines between telco closets or to remote locations. It saves money rather than running individual cables.

If one line per cable, what is the proper thing to do with the un-used pairs on the telephone block in the closet?
..They are typically wrapped around the outer sheath or you can punch them down to keep in reserve. You may want to add another line to that location, such as for a phone that can handle multiple lines.

If multiple lines per cable, what is the best way to break out the lines on the users side to connect to telephones in a neat way?
..The best way to break out the other lines is by using the 66 cross connect and then running individual cables to the phone jack, that could be Cat3 or Cat5.

I guess it may not make sense but the cable from the last 66 cross connect to the individual phone jack will have unused pairs. Unless you want to daisy chain from one phone jack to another one, rather than run a completely different cable from the 66 cross connect.

by mikey.g.0727

Thats what i was really looking for.

I noticed you used 66 Blocks in your explanation, and not 110 blocks... My digging indicated that a 110 block is rated to support Cat5e standards, while 66 block is not.

If this is so, why would you use a 66 Block?

Thank You! Great Information!

by michael kassner

Remember you are using Cat5 but do not need that rating for PBX telco conditions.

Even so I still would use a 66 block for cross-connecting in a telco situation, I suspect a die hard telco type would skin you alive if they saw a 110 block being used to cross-connect telco lines. It is a great deal more cumbersome to work with as well.

A 66 block is stand alone and if you notice there are 4 punch downs per row. That allows you to inter-connect between cross blocks or across the row of 4 punch downs. In the link you can see the metal bridges being used.

http://en.wikipedia.org/wiki/66_block

by churdoo

I've been watching this thread. Michael K, great information!

Mikey.g, time to give this man some thumbs up.

by mikey.g.0727

Done - I didnt realize right away, that thumbs up was literal... Lol. You are right, the info is great, and its hard to find good info on such topics..

by michael kassner

More to the point though, did my post make sense? I guess I tried to point out that there are two different methods to cross-connect on a 66 block.

One method is where one pair is installed on the metal punch downs right next to the outside plastic guide. The second pair that you want connected to it are then installed on the metal punch downs closer to the middle of the block. This method is especially used if the cross block has an pre-attached cable and the pairs from the pre-attached cable are usually in the punch downs nearest to the outside plastic wire guides.

One other method that is used, is where the pairs are installed in the metal punch downs nearest the outside plastic guides as in the first method and the pair you want to connect to it installed on the other side of that same row nearest the outside plastic guides and you use a metal bridge clip to inter-connect them.

Hope I did not over-explain, it is just a bit confusing and as you mentioned this information is not readily available.

by mikey.g.0727

Your post makes perfect sense to me, because I am familiar with a 66 block.

It should be pointed out, that 66 blocks come in 2 flavors (that I know of), split and unsplit, while all 66 blocks have rows of 4 contacts, connectivity is as follows-

Split -

a a b b
c c d d
e e f f

Unsplit -

a a a a
b b b b
c c c c
d d d d

On a split block, you use bridge clips over the 2 middle contacts, to connect the outermost contacts on a given row.

i think it is strange these things are so hard to find good info on. I think its because most of the time in a big installation this would be done by an electrician who wires teleco / data, and those jobs are usually apprentice-ship type of profession.

Ther are 100 million web sites that describe the pinout of a cat 5(e) so you can crimp your own cable, but almost none that tell you what do do with the cable when its done :-P

If anybody has any other tips / tricks / good info sources on this type of stuff for wiring Data / Voce - post em up.

Another tid-bit for ppl doing wiring in small offices - Plenum Vs PVC Cat5(e). "standard" cat 5e outer jacket is made of PVC, which when burned, releases toxic fumes. Because of this, MOST local codes require use of plenum cable, the coating does not release such fumes (but the cable costs a lot more :) )

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