What is Line Seizure?
Standard digital communicators use a regular dial tone phone line in order to send their signals to the Central Station. An alarm message is somewhat like a fax transmission, with a dial sequence, a handshake, a data transmission, another handshake and a hang up. If the line is in use when an alarm message starts, or a phone instrument is left off hook, there needs to be a way to clear the line and over ride all other call activity. Otherwise, the signal could be seriously delayed or blocked completely.
Most security systems are wired to the phone line through what is known as an RJ31X phone jack. This 8-pin telephone jack is specially designed to provide Line Seizure. The phone line comes to your building from a terminal block on a utility pole or in a pedestal along the highway. It runs overhead or underground to a Network Interface block on or inside your building. Without a security system, all of the individual cables and jacks for house phones, computer modems, answering machines, fax machines, etc., are connected directly to the Network Interface block.
When installing a monitored security system, the cables for all of the jacks and devices are lifted off the block. In their place, a new cable pair takes the dial tone line to an RJ31X jack usually located in the immediate vicinity of the alarm box. A plug-in cable takes the dial tone from the RJ31X to "Line In " terminals on the communicator module. An electrical relay in the communicator switches the line to the communicator itself just during alarm transmissions. When there is no alarm transmission in progress, the relay allows the dial tone to pass through to the "Line Out" terminals of the communicator. Another pair of wires in the plug-in cord returns the dial tone to the RJ31X jack. A separate cable pair takes it back to the Network Interface box. At the network Interface box, the returning dial tone is connected to the wires for house phones, etc. that were taken off the incoming terminals of the Network Interface earlier. That connection is often "floating," that is, it has no fixed screw terminals. It can be a pair of wire nuts, crimp connectors or a special plug assembly. It could also be a separate block or an otherwise unused pair of screw terminals inside the Network Interface box.
Two big Problems:
Phone technicians who are troubleshooting the line may be confused by this arrangement unless they know you have it. One of their standard troubleshooting measures is to disconnect the cables for your various telephone instruments from the block one by one, until the trouble clears up. Occasionally, when they are done, the RJ31X jack ends up disconnected or wired wrong.
A second frequent occurrence is for new phone jacks, fax jacks, etc. to be connected directly to the incoming terminals of your Network Interface block. This defeats the Line Seizure function. If you leave one of these improperly connected devices off the hook, it will tie up the line. The communicator's relay will be unable to clear the line to send signals.
Make sure all phone installers know you have an RJ31X connected to your line.
Some situations make it impossible to achieve Line Seizure:
Sometimes the Network Interface is in a part of the property that is too remote or inaccessible to run a cable run from the alarm box, or it simply can't be found or identified. Many apartment buildings do not have Network Interface boxes in the individual apartments. In that situation, an installer may have to tap into an existing phone jack.
If you have a phone line that has jacks in more than one building ("dual service"), the junction may be at the phone company's Central Office, on a utility pole, or in a pedestal controlled by the phone company, making it impossible for the alarm installer to intercept the line ahead of all phones. This is most common when people are preparing to move. In that situation, the installer should at least be able to achieve line seizure within the one building where the alarm panel and RJ31X are located.
It is important to test your system's communicator after any work has been done on your phone system. If you don't know how to do it, we have a guide we can fax or mail to you, or you can get it from this site. The procedure only describes how to test the communicator, not how to check for Line Seizure.
To Test for Line Seizure:
Set up a test with the Central Station following the instructions in the Test Procedure mentioned above. Allow plenty of extra time, especially if you have a lot of jacks to check.
Have someone pick up the phone you wish to check for line seizure. Immediately trip an alarm signal using one of the methods mentioned in the communicator test procedure. The phone being checked should go dead and remain dead during the alarm transmission. In most cases you should not hear the communicator's dialing noise or data transmission. (If you do hear anything, it should be very faint.)
If the line goes completely dead, the test is successful.
If you hear dialing clicks, touch tones or the data exchange clearly, the test is not successful. Call us for a review of the test procedure you used and the results. We will recommend a course of action.
When the signal transmission is done, dial tone will become available at that phone again. Go to another phone that you wish to check for line seizure, and repeat the process. Check each and every instrument, including fax and answering machines, Caller ID boxes, computer modems, credit card boxes, etc. If there is no actual telephone handset or speakerphone on a device you wish to check for line seizure:
Method #1: Most fax and answering machines, modems, etc. will have a "Line" ("In") and a "Phone" ("Out") jack on them. Plug the regular cord into the Line jack as usual. Plug any ordinary telephone into the "Phone" jack, then do the test. Make sure the phone device and the line being checked are idle.
Method #2: Unplug the device being checked from its wall phone jack and plug any ordinary phone into the wall jack for the test.
Note that some regular 4-prong phone jacks have two different phone lines in them, which could make Method #2 invalid and may also interfere with calls on the second line.
Copyright © 2000
Luis Arellano, III. All rights reserved.
Revised: February 06, 2008 11:04