Splitting Horizontal Cabling for Voice

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 Question by Troy Greene posted 18 Jun 2000
 Splitting Horizontal Cabling for Voice
I have defined the work area cable drops specs for an upcoming project. Each work area will have 3 data cables (Cat5) and 1 voice cable (Cat3). I proposed the cabling contractor terminate voice cables on 110 style blocks on wall near telco demarc as the horizontal cross connect. The contractor suggested terminating the cable into 2 outlets at the work area. It makes sense to do that once the phones use only 1 pair. Aren't you suppose terminate the CAT 3 cable into a single outlet and use an adapter if you wanted access to 2 pairs on cable for connecting 2 devices say a telephone and modem. I can understand why you wouldn't want to split the data cables but not for voice. Older voice systems required 2 pairs for phone connections. Newer systems such as the Nortel PBX we have only use pair. I'm confused. What wiring scheme (USOC or T568B) and number of outlets shall I use for voice (Cat3) cable. If there any published standard(s) regarding this. Thanks
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 Answer by Roman Kitaev posted 19 Jun 2000
Hi, Troy!

I think the best answer is the ANSI/TIA/EIA-568-A standard.

It states that splitting one cable into two outlets is not allowed. Each work area outlet shall be served by the dedicated cable. That means that you should terminate each Cat3 cable to one outlet.

In addition, the standard allows two horizontal wiring schemes: T568A and T568B. In your case, follow T568B.

If you need additional voice outlets, just use external splitters. The reason why the standard dictates "one cable - one outlet" principle is simple: "the horizontal cabling should facilitate ongoing maintenance and relocation. It should also accomodate future equipment and service changes". It may happen that in the future you will need to use your cabling for other protocols than you are intending now. For this, The standard tries to ensure some universality.

Best regards,
Roman Kitaev, RCDD

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