Installing A DSL Splitter With An Alarm System


If you have an alarm system, you should use a splitter so that the DSL data is separated from the voice signal that goes to the alarm system RJ 31X jack.  That prevents interference originating in the alarm system connection from interfering with the DSL service.  It also allows the alarm system to seize the voice line when an alarm condition exists, without dropping the signal to the DSL modem.  Using a splitter in your DSL installation with a dedicated cable for the DSL data connection also avoids sending the DSL signal over the alarm system phone cable, which is normally low quality cable that is highly susceptible to interference.

Alarm System RJ-31X Jack Connections

Standard practice for alarm system installers is to run a cable from the NID to an RJ 1X jack located with the alarm system.  One pair of the cable is used for the connection from the NID to the line side of the RJ 31X jack.  A second pair in the cable brings the line from the drop side of the RJ 31X jack back to the NID and is spliced to the inside wiring, normally using crimp splices. 

DSL Splitter Installation With An Alarm System In A Bus or Hybrid Topology Phone Wiring

If you have a bus or hybrid topology telephone wiring installation, it is normally easiest to use an outdoor splitter near the NID.  A new cable is run from the NID to the network terminals of the splitter.  The alarm system phone cable and voice cables are moved to the splitter enclosure.  The "line" pair (normally green/red) of the alarm system phone cable is connected to the "phone/voice" terminals of the splitter and the inside cable to the voice jacks is spliced to the alarm system "drop" pair (normally black/yellow).  Then a new cable is run from the splitter data/modem terminals to a jack for connection to the DSL modem. 


DSL Splitter Installation With An Alarm System In A Star Topology Phone Wiring

If you have a star topology telephone wiring installation and your alarm system is connected to the phone line at the NID, you have the option of using an outdoor splitter near the NID.  As shown below, this is almost identical to the bus/hybrid installation and still requires running a cable for DSL data all of the way to the splitter. 

You might note that the two configurations shown above are not actually dependent on using an outdoor splitter near the NID.  You could use an indoor splitter located at any indoor location where you can access both the alarm system phone cable and all of the cables going from the NID to all of the existing cables to the voice jacks (or the cable from the NID to the wiring hub if you have a star topology).  It might be easier to route the cable for DSL data to such an interior location than all the way to a location near the NID.  However, if you have a star topology, making all of your connections at the wiring hub, as shown below, is probably a better option.

DSL Splitter and Alarm System Connections At The Star Topology Wiring Hub

If you have a star topology installation and can easily reroute the cable for the alarm system phone line cable to your wiring hub, you might want to consider making all of your connections at the star topology wiring hub.  This would permit using an indoor DSL splitter and the cable to the jack for connection to the DSL modem would only need to be run from the wiring hub to the modem location, which is probably easier to accomplish. 


At the left is an illustration of an example 66-block arranged for an alarm system and DSL splitter installation.  The exact arrangement of your block would vary according to your particular installation, but would be similar to this example.  Note that this example is very similar to the example shown at DSL Splitter Installation in a Star Topology, except that it has been modified to show the alarm system connections. Here are the connections shown on the example:
  • The cable coming from the NID is terminated on binding post pairs 1-4
    • Pair 1 is unused. (Would have been line one before DSL was installed.)
    • Pair 2 is line 2 (if present).
    • Pair 3 is unused.
    • Pair 4 is the DSL line.
  • The alarm system phone cable is terminated on binding post pairs 26 and 27
    (at the top on the right side of the block).
    • Binding post pairs 28 and 29 remain vacant to allow for changing to a four-pair cable.
  • The cable to the splitter is terminated on binding post pairs 30-33.
    • The DSL line is cross-connected from pair 4 of the NID cable to pair 4 of the splitter cable.  This pair would terminate on the "LINE" connection on the splitter.
    • Pair 1 of the splitter cable would terminate on the "VOICE/PHONE" connection on the splitter and is cross-connected to pair 1 of the alarm system phone cable (the "LINE" pair).
    • Pair 2 of the alarm system phone cable (the "DROP" pair) is cross-connected to the first pair of all the station cables to connect telephone line 1.
    • Pair 3 of the splitter cable would terminate on the "DSL" or "DATA/MODEM" connection on the splitter and is cross-connected to the cable going to the location where the DSL modem/router will be located.
  • In the illustration, the cable on pairs 5-8 is used for the location for the DSL modem/router.
    • Pairs 1 and 2 would go to a jack for connection of a telephone.
    • Pair 3 would go to a jack for connection to the DSL modem/router.

    • (A dual jack faceplate could be used so that both jacks fit in the existing space.)
  • Pair 1 of all the station cables are all cross-connected to the "DROP" on pair 2 of the alarm system phone cable.  Pair 2 of all the station cables are all cross-connected to pair 2 of the cable coming from the NID to provide connection to a second phone line if it is active.  If your DSL line is "line two", this would be adjusted accordingly.  I would recommend installing the cross-connect for the second line even if you only have one line.  This will make it simpler and avoid confusion if a second line is added in the future.
Click on the graphic for the wiring block to see a larger version of the graphic.


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