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I need to install a dedicated line for a security system with a Rj38X Connection.  i am not familar with this type of connection.  How would I go about installing this jack




Its been a while but if i recall correctly that jack has a shorting bar in it that closes if the connection is unplugged. It installs like a standard jack.


do you mean a rj 31X ?

  thats whats usally used for alarms , like bobg says it has a shorting bar so if you unplug the alarm you dont lose dialtone.

  simplest thing is to buy one from a alram supply I put in a couple here last month and I beleive they were 2.50 each

  wiring diagrams are molded right into the covers.

  re reading your post I see your saying its a dedicated line in that case I beleive you can just use a standard 8 conductor biskit jack without the shorting pins


A RJ31X and a RJ38X are the same thing. Pins 4 and 5 short to pins 1 and 8. Line goes in on 4 and 5 and out on 1 and 8.

Good Luck!!


excellent thanks



Minor difference between the RJ38X and RJ31X.  There is a strap between pins 2 and 7 on the RJ38X.  Presumably this is used by the alarm equipment to determine when it is plugged in to the jack, and when it has been removed from the jack.



what do I use to do this with?


what do I use to do this with?

  best to just buy a rj38x jack should be able to get them from a alarm supply company like ADI

  I needed to run some RJ31x a few weeks ago and graybar didnt stock the jacks but had to order them in .

  I got them from a local alarm Distributor  for about 2.50 each.  Radio shack may evan have them you could check with them


I asked my alarm guy about these jacks. He said that on older systems they cant tell if the plug from the alarm box is disconnected, but if a burglar cuts the wire to any jack, it can still can the police. i am curious as to what would happen on a newer system if you had to disconnect the NID for repair work. Anyone had to do that in an alarm system (that doesnt have its own line)?

jeff moss


What you are referring to is what we call supervision in the alarm business.  In older simple panels, they were not smart enough to sense the idle 48 volts or active 6-10 volts on the phone line.  So, adding a resistor in the loop through the jack itself, the connecting this loop across an input zone, you get supervision.  If that jack is unplugged, the panel doesn't see the supervision resistance, and goes into trouble.  Often this is a 'tamper' situation, in commercial installations we tamper all devices.  Otherwise, the employee could open the panel, disable the alarm while on duty, then come back at nite with the key and unload your stuff.  So, we have tamper switches on the devices and the panel that prevent anyone opening devices and such without authorization.

The purpose of the RJ-31X is two-fold.  First, it is designed to disconnect everything downstream from the panel (i.e. all the phones in the house/business) so that the burglar can't interupt the phone call.  Second, they allow the panel to take over in the event of an emergency and interupt communications on that line.  The panel will sieze the line, draw a new dial tone, and call the alarm monitoring center even if the line was in use for a voice call.

Now newer panels will monitor the voltage on the phone line input.  Most are programmable for how long you want to have it wait before reporting the line as not present.  Generally we set those to 15 minutes or so.  Then you have the choice to make the system go into trouble or alarm.  Normally we choose trouble.  So, if you were rebuilding the NID or splicing or something and took dialtone away for over 15 minutes, the panel would beep inside indicating a loss of phone line. Often the telco's i deal with will take a line down for several minutes for testing/splicing, etc.  Of course, if the crook cuts the line before the NID and then breaks in, it won't be able to call the police.  You are dependant on a local siren alarm to get attention from the neighbors, or a back up cellular phone connnected to the panel.

Hope that helps.

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD


that definately helps. the way my house was wired 25 years ago is such a mess, cant figure out anything (except in my super neat basement shop)

jeff moss

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