Wiring RJ31X Jack

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DIY Alarm Systems / DIY Security Systems

Tennessee Alarm Store


RJ31X Line Seizure Jack

What is a RJ31X jack and what does it do?

RJ31X JackWhat is the purpose of the RJ31X jack? Well, the technical answer is it provides line seizure for the incoming telephone line. OK, that sounds like, "Wah, Wah, WHAT?" Simply put, this means that the DIY alarm system takes over the telephone line and disconnects all phone equipment that might be located on the premises. This can include all corded phones, cordless phones, fax machines or any other item that uses the incoming telephone line. This prevents anyone from taking a phone off the hook or ripping it out of the wall in an attempt to defeat the alarm system. Once the alarm data has been sent to the monitoring company the alarm releases the line, reconnects the phone equipment, and restores the phones to normal operation. If you need to work on the alarm panel you may disconnect the 8 pin modular plug from your RJ31X, and it will automatically reconnect your phones while you do your work.

I should mention here that the DIY alarm system constantly monitors the phone line on a 24 hour basis. Whether it is armed of disarmed, this monitoring takes place. Depending on how the alarm is programmed, it can sound the siren or alert you on the key pad that there is a problem with the phone line. Imagine the surprise to a burglar when he cuts the phone line and the siren starts blasting away.

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How do I properly wire in the telephone with an RJ31X jack?

Telephone Network InterfaceYou must first find where the telephone line comes into your premises before any extensions or equipment is hooked up. This may be underground or overhead, but you should be able to locate the outside telephone network interface device. Let's run a 4 conductor, 22 gauge cable between the telephone network interface device and the location you chose for your control panel. We will work on the control panel first so we won't have the telephones down any longer than necessary. (I don't know about you, buy my wife goes crazy without a telephone.)


Fork Terminals RJ31X JackLocate the 8 wire cable with the modular plug on the end of it. We will only be USING the RED, GREEN, GREY and BROWN wires. Cut the terminals off of the UNUSED wires, pull the insulation out past the wire and tape them to the cable, ensuring none of them are shorted together. Next, carefully cut off one leg of the spade terminals on the RED, GREEN, GREY and BROWN wires. (See drawing to the left) Connect the wires to the alarm panel as follows: RED to RING--, GREEN to TIP--, GREY to R1-- and BROWN to R2. Leave the other end of this cable with the modular plug unplugged for now.


RJ31X ConnectionsNow carefully pry off the cover of the RJ31X and observe the 8 pre-wired terminals. There should be terminals with RED, GREEN, GREY and BROWN wires under them. The other terminals will not be used. Strip back about 2 inches of the outside jacket of the cable you ran between the telephone network interface box and the alarm panel. Strip back about 3/4 inch of insulation from each wire and form a hook. Place the RED wire under the terminal with the pre-wired Red wire on it and snug it down. Do the same with the GREEN wire on its appropriate terminal. Now it starts to get confusing, but bear with me. You probably have a BLACK and YELLOW wire left in the cable that are not connected yet. Hook the BLACK wire under the terminal with the pre-wired GREY wire on it. Now hook up the last wire in the cable. It goes YELLOW to the pre-wired terminal with the BROWN wire on it. To check the wiring, make sure you left the RJ31X unplugged from the alarm panel, go outside and strip back the wires as you did before. If you have a volt/ohm multi-meter, set it to RX1 scale. Check the meter by touching the leads together. You should get 0 ohms resistance or close to it. Now touch the RED wire to the BLACK wire and you should get a reading below 0-3 ohms. Do the same to the GREEN and YELLOW wires and you should get the same reading on the meter. If everything checks OK this tells you that you wired the jack correctly. If not go back and check all your connections.

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A word about SAFETY before we continue. Telephones can have higher voltages than the 12 volts DC we are accustomed to working with on the alarm panels. Telephones have close to 50 volts DC when they are on hook. (Not being used) They can have even higher voltages when they are ringing. Approximately 90 volts AC is super imposed on the DC voltage during the ringing of the telephone. Please exercise due caution when working on the telephone network interface device. Do not work on this device during damp conditions or during an electrical storm.

telephone connections in NIDNow we will finish the wiring at the telephone network interface device. Unplug the modular test jack in the telephone interface panel to isolate you from the incoming line. Locate the Red and Green terminals in the customer side of the interface panel. There may be 2 screw terminals for each color, however, these screws are electrically tied together by a shorting bar. Disconnect all wires coming from your house phone(s) (1, 2, 3, 4 or more) from the terminals on the RED side. Wrap these wires together because we will cap these wires later. Now connect the Red wire coming from the cable we added to either one of the red terminals and snug up both screws. Connect the GREY wire out of our cable to the twisted wires we removed from the RED side terminals. Make sure they are all twisted together, ensuring each has a good electrical connection. Place a crimp cap or other type of electrical connection over the wires and crimp the connection. If you did not use an insulated crimp connection wrap these wires with electrical tape. Now we will repeat this operation for the GREEN side. Disconnect all wires on the GREEN side coming from your house phones and wrap them together. Connect the GREEN wire from our cable to either screw on the GREEN side of the telephone interface device and tighten the screws. Connect the BROWN wire from the cable to twisted wires you removed from the GREEN side terminals. Cap, Crimp and insulate the connections. You have now completed the installation of the RJ31X jack. Your phones should now work as they normally did.

There are many different types of telephone interfaces in use today and they may not look exactly like our example. If you have an older home you may not even have a test jack. You may have just a protector block with a lightening arrester. You may call the phone company and request this to be upgraded to a network interface device (NID). There should be no charge for this upgrade but it may take a few weeks for a technician to get out there. It is impossible to tell exactly which telephone network interface device you have, however, the drawing at the left should make it clear how to wire in the RJ31X telephone jack. If you find you are having any problems at all, feel free to call us at 1-423-562-1927 or e-mail us utilizing our Contact Us page.

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