From: "Bring ring" Subject: BT CAB TEXT updated/corrected Date: 07 October 2001 09:16 ---------------------------------------------------------------------------- BT Wiring Cabinets By Cold Fire UPDATED Oct 2001 By "Self Motivated Team" ---------------------------------------------------------------------------- BT CABS I'm sure you're all familiar with the green BT wiring cabinets, this file sets out to explain the use of these to find or identify a particular line, using the necessary BT equipment and test facilities. First of all, with so many cable operators coming on the scene, don't assume that what you are looking at is a BT cab. 99% Of BT Cabs use the triangular pillar door lock. Cable companies DO NOT. BT cabs come in various designs from the old cast iron box through some steel shells and up to glass fibre. They all open with the same tool. The key difference inside them is the way that the terminations/connections are made. The cabinets are known within BT as PCPs (Primary Connection Points or Primary cross-connection points) and are usually secured with two triangular screws the BT tool to open them is known as a "key cabinet 1a",although they can be opened quite easily with a wrench though. Some cabinets are kept locked, usually in high risk areas, when engineers need to work on these they use a high security key.(Similar to an exchange key) While the cabinet may seem to be mess it is a reasonably ordered mess. Most cabinets have what is called a 'speaker pair' within. This is just a line to the cab that an engineer can use to make calls on. This is identifiable by two screw terminals colour coded red and black. Some of the newer cabs have a BT socket (NTE5) but this will usually always go to the screw terminals. The cab is also fitted with pressure gauges. These are connected to an alarm line in most cases. The pressure gauges monitor the pressure in the E side (or exchange side) cables coming into the cabinet. Air is pumped through them to keep moisture out. As an E side cable can accommodate thousands of pairs, any moisture in it could cause major disruption if a failure occurred. To understand how a cab is laid out a little network understanding is necessary. First of all, the purpose of the cabinet is to connect local customers to the exchange. A single exchange will have many cabs within it's area. Each cab is 'fed' by a series of E side cables. They are connected to a bar pair in the exchange and jumpered through to the physical 'switch' and equipment. On the other hand, the customer, is fed going away from the cabinet on D (distribution) side cables. These are smaller and not pressurised. They are protected from moisture by a grease similar to Vaseline. The D side cables run underground and overhead along the streets to DP's (distribution points) where the customers lead-in (or cable to their premises) begins. DP's can be at the top of Poles, or underground or internal. The whole purpose of the cab is to allow easy cross connection of D Sides to E sides. This is achieved by running a small length of jumper wire (yellow/blue newer cabs - red/blue older cabs) from the cab E side to D side. You will rarely find ANY plans or data inside the cab as an engineer visiting will have routing details available to him, and test gear if he does not. A cab can feed up to 1000 lines or customers (more if you add DACS into the equation) but typical is 4-500. A word of warning! The cabinet NEAREST the premises is not always the cabinet that feeds it. It is Usually the case but in areas where new homes have been built (and by new I mean within the last 30 years - bear in mind the BT network has been in the ground for close to a century) it is common to see a cab a few meters from a house that is being fed by a cabinet a kilometre away. Cab termination's and organisation: Cabs have several types of termination's in them but no matter what type are inside it is split into E sides and D sides. The birds nest type has a plastic strip where the wires poke through tiny holes. A close look at these will show you they are numbered. Left of strip E side, Right of strip D side. These strips can be 100 or 200 pair holders. That is 100 E sides and 100 D sides / 200 E sides 200 D sides. The E to D jumper is CRIMPED with a little white bead crimp. You may also find the old screw terminal variety. E's on the left D's on the right. These are NOT always jumpered. If, for example the routing is Cab 8 E side 96 to D side 96 the block is 'straight pinned' with little yellow headed pins being pushed all the way through to join the E and D together. If you play with these old strips a couple of things to know. First of all, the screws are PER pair. They have no electrical contact with the wires. They just push a clamp down to grip them hence 100 pairs (200 wires) have 100 screws. These screws are also SHEARING screws and you do not do them up tight or the head snaps off! Finally, left is E right is D BUT be aware that you can push a wire through the E side into the D side so don't strip them off too far or push them in to far. 1 cm is enough. Turn the screw lightly until it just bites. Finally, several modern cabs use IDC strips from Krone/Quante/Bics/3M. These are different as the E sides and D sides are physically NOT on the same terminal blocks. Left is E, right is D but they usually are scribbled on to confirm (D 1-10) etc. You can use a small screwdriver to make connections much like a BT socket, if the correct tool is not available. Locating a specific line. As long as the line is in the cab you can find it. You will need a BT amplifier to do so if you do not have the routing. These are inductive amps with a probe on them. Available from: http://www.chesilvale.textron.com/ To find your line clip a test phone onto the speaker pair, Dial 17070, and select 3. Wait for the 'press 1 if you have been authorised' to finish and press 1. Select 3 "Cable pair identification" from the menu. You will need to enter the number of the line you are 'looking' for followed by #, then 1 to confirm, 1 for non PABX. This will NOT work, by the way, if you try to tone the line you are using so all those claims about it hanging people up and stuff is rubbish. If the line is in use/engaged it cannot progress.After cocking around you will finally hear 'test tone' every 30 seconds. The CPID will run for 3 minutes then require that you re activate it. Run the probe slowly up and down the pairs. When you find the line you'll hear "Bleep Bleep Bleep Bleep...." Much like a metal detector homing in. To confirm that it is the pair just gently squeeze a pair of wire cutters on it to short the pair together. When shorted the tone will stop and after a moment the 17070 Rats system will say "The tone has been tripped". That's the line. Useful for nosey partners, finding phone box pairs etc. Original article by Cold Fire. Updated Oct 2001 by a Self Motivated Team. NB 17070 can also be accessed from a mobile/other by dialing 0800 373983 or 01223 369997