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TUCoPS :: Phreaking General Information :: btwiring.txt

BT Wiring Cabinets


                             BT Wiring Cabinets

                                By Cold Fire


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.

The cabinets are known with in BT as PCPs and are usually secured with two
triangular screws the BT tool to open them is known as the keys pillar,
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 have to get the keys from their control first, there is no master
keying as far as I know.

While the cabinet may seem to be mess it is a reasonably ordered mess, in
the top right hand corner is the cabinet speaker pair, which to quote the BT
manual on installing them is 'a dedicated speaker pair terminated on an NTE
5A and with a separate, labelled exchange line connection', basically just a
BT phone socket, this is a separate line with its own number (usually on a
label on the socket, or listed in the cabinet address book). This is usually
used for customer pair localisation (CPLE) calls. Below this are the
pressure gauges. the whole left hand side and centre of the cabinet is made
up of the customer pairs, which are usually labelled, if not look in the
door of the cabinet where there is often a clipboard with the wiring

To identify a given pair, attach your linesman phone to the pair and dial
175, this is known as Customer Pair Identification (CPI) and a voice will
read back the number of the pair you are calling from. This also
incorporates a line test (SALT) with will call you back after you hang up
and tell you the condition of the line, then ask you to dial next text which
are :

Subscribers Apparatus Line Test (SALT) facility (Taken from Uk.telecom FAQ)

DIGIT 1 (Dial Test) - Expects "123456789*0#" to be dialled
DIGIT 3 (CCB Test)  - Sends 'open slots' + pay tone to line under test.
                         Expects coin insertion indication from line
                         (Measures coin insertion signal characteristics
                         and checks result)
                         Sends coin pulse ACK signals to line
DIGIT 4 (SPM Test)  - If SPM is provided on the line 50Hz SPM
                         5 long SPM pulses sent to line followed
                         by NU tone. 1 second time-out then 5 short
                         SPM pulses. 16KHz 10 pulses of nominal
                         characteristics sent to line without burst on NU tone
DIGIT A (MF4 extra) - Expects "ABCD" to be dialled.

If a linesman wants to find a particular pair then he will use an
oscillating tone and an amplifier with an acoustic probe. The method used
will depend on which side of the pair he wants to find.

To find the exchange side, i.e. the wires coming from the exchange for a
particular number, he would attach his lineman's phone to the cabinet
speaker pair and dial 176 + the full national number of the pair he wants to
locate (this is known as the Customer Pair Localisation Equipment (CPLE)
this will cause an oscillating tone (1khz (50 milliseconds on 100 ms off) to
be send from the exchange down the pair to the cabinet. This can then be
located with a BT Amplifier 105G and acoustic probe. This is just a yellow
box with a head set and a probe on the end of a wire, the probe does not
have to be in contact with the pair to find the tone but can be moved across
the banks of pairs in the cabinet, adjusting the sensitivity of the
amplifier will allow the pair to be located quickly.

To find the customer side, i.e. the wires going from the customers premises
to the cabinet the linesman cannot use CPLE so must use a BT Oscillator to
generate the tones, there are two models of oscillator, one small (87G) and
one large (87F), and I believe the main difference is the power, and thus
the range. Both are adjustable from a short beep to a continuous tone (note
these are not the types of oscillator you see in labs but merely produce a
tone and have no display, the smaller one can be easily fitted into a
pocket). The engineer will attach the oscillator to the pair in the customer
premises, then return to the cabinet and use the amplifier to locate the
pair as mentioned earlier.

All of the above instruction apply to TXD X (System X) exchanges. TXD Y
(System Y) exchanges have Faultsmens Ring Back (FRB) only, on 174. This has
a line test included in it. Dial code; dial tone returned: replace reciever;
bell will ring (could be a delay of up to 40 seconds; lift reciever - if
dial tone heard line tests OK: if interrupted tone heard, line is testing
faulty; replace receiver. Test terminated.

For other exchanges e.g. TXE2, TXS/TXK3, TXE4s the test number can change
from exchange to exchange.

Hope all this is useful. Most is distilled from personal experience and BT
training guides and dial up facilities lists.

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