Internal Telephone System No. 3 had a sales name of PROTEUS 24 (24 ports) and PROTEUS 64
Information on this product can be found in TI's B4 N0011 Description and Facilities, C3
M4010 Installation and Customers Apparatus Guide Notes - Proteus 24 and 64
The system is space switched based on a Central Switching Unit (CSU) which utilises
"Complementary Metal Oxide Semi Conductor (CMOS)" solid state technology. The
system is available in two sizes, 24 and 64 extensions and the CSU for both sizes measures
472 x 276 x 353 mm (1822 x 11 x 14 in), and weighs 7Kg (19lb. approximately). The CSU is
free standing and is suitable for handling by one man. Growth of the system is achieved by
the provision of additional Apparatus Slide-in Units (ASUs).
Extensions are wired from the CSU using single pairs of wires and numbered in an octal
manner. Any British Telecom standard 10 pps telephone may be used and most existing Plan
arrangements can be provided at the extension terminals. Generally, battery type Press
Button Telephones should not be provided, but if they are, power unit charging must be
adopted. Line charging is not suitable as Proteus is a 30 volt system and the telephone
Charge Switching Unit is intended for 50 volt working therefore it will not switch on to
charge the telephone battery.
The system is mains powered and completely self-contained. No external source is required
for ringing or tone supplies.
In the event of mains failure all calls are lost and there is no provision for standby
power. However, the system automatically restarts when power is restored.
Maintenance of the common circuit elements of the Central Switching Unit is appropriate to
the Technical Officer (TO) grade, while extension telephones, wiring and line interface
units of the CSU are appropriate to the Technician 2A grade.
To minimise the number of double visits, clear instructions should be available in RSCs
(Repair Service Control) enabling the appropriate grade of staff to be directed to deal
with particular reports, e.g. TO for system off or general difficulties common to a large
number of telephones, T2A for single telephone faults. When the nature of a fault is
uncertain a T2A may be sent.
The aim is to restore customer service as soon as possible. The complex Technology used
and the high density of the components does not make the system suitable for on-site
repair. Routine maintenance is not required and there are no inbuilt maintenance and
diagnostic tests. Maintenance is corrective only using a logical process to identify the
faulty unit, and changing it out for a working spare. It is possible to provide
maintenance spares kits to cater for the majority of situations taking into account that
Technician IIA deal with telephones, interface units, and cabling in between; with
Technical Officers dealing with common control elements of the system.
No special tools are required for maintenance, but an extractor is provided on the back
panel adjacent to the spare set of fuses to aid in the easy removal of the ASUs.
Modular construction techniques are employed enabling disruption to service arising from
CSU failure to be cleared quickly by interchange of units. Guidance in the location of
faults is given in Appendix 1 and the Logic Faulting Chart at the end of this Instruction.
When faults are not cleared by applying these procedures the complete CSU may be changed.
Maintenance of the distribution wiring and terminal apparatus is as normally practiced at
PBX installations. The outputs of the Power and Ringing supplies are not earthed and
testing on the system should be across the pairs of wires and not line and earth.
Anti Static Precautions
As electrostatic sensitive devices are used in the CSU the following precautions should be
(i) Discharge any body charge by occasionally touching earth before removing any ASU.
(ii) Handle all ASUs by the handles provided.
(iii) Do not touch the circuit track or components.
(iv) Place all ASUs in Anti Static Bags inside the original packing before transporting.
Access and Removal of Units
Access to the front of the CSU is gained by slackening the captive fixings positioned at
the corners of the front panel.
The CSU houses the following equipment.
NOTE - The Power Supply Unit develops dangerous voltages
(i) Power Supply Unit (Black Handle) Capable of supplying a fully equipped system. Removal
of the Power Supply Unit (PSU) and access to the back wiring is via the back panel.
BEFORE ATTEMPTING TO REMOVE THIS PANEL DISCONNECT THE MAINS SUPPLY AND REMOVE THE MAINS
PLUG FROM THE MAINS SOCKET.
To remove the back panel slacken all captive screws around the outside edge. With the
panel removed the mains connector to the PSU can be unplugged and the single fixing screw
retaining the PSU removed. The PSU can then be withdrawn from the front.
When removing the PSU care should be taken to secure a firm grip on the handle provided as
the heavy mains transformer is fitted to the rear of the unit.
(ii) Line Interface Unit (Blue Handle) One required for each eight extensions provided.
Consists of a mother/daughter board which houses the basic 8 x 8 switching array and the
line interface for eight extensions. Each extension circuit is provided with a small
switch on the ASU. For normal operation the switch should be in the forward position
towards the front of the ASU. If an extension has not been provided the switch position is
towards the rear of the ASU resulting in the return of Number Unobtainable (NU) tone if
(iii) Common Control Unit (Red Handle) One per system. Provides timing and control of the
system. Generates all tones required, i.e. dial, busy, NU and ring. Eight small switches
are provided enabling individual Call Connect Circuits to be busied if required for
testing purposes. The switch number corresponds to the Call Connect Circuit number. The
switch positions are towards the rear of the ASU for normal operation and forward for
busy. A small LED is also included which flashes at regular intervals when the system is
(iv) Call Connect Unit (Yellow Handle) Two connect circuits are provided on each unit and
provide the necessary connecting circuits required for calls. Two small LED's are provided
to indicate circuit busy.
NOTE - The first ASU position provides Call Connect Circuits 1 and 5, the second provides
2 and 6 etc along the four positions of the CSU.
Removal of ASUs requires the use of the Extractor.
When a Proteus system is installed it is essential that a supply of maintenance
replacement items are available. For up to 10 systems one complete set of spares listed
below should be held and the percentage holdings of individual items adjusted according to
trend as the number of systems in use increases.
Description BT ITEM CODE
Case 246A Includes 24 way backplane} 435995
Case 246B Includes 64 way backplane 435996
Power Unit 155A 314364
Common Control Card ASU/1A1/FDH/16891 418051
Dual Call Connect Card ASU/1Al/FDH/16900 418052
Line Extension Cards ASU/1Al/FDH/16894 418053
Cable Connection 14A 435997
C MARKETING INSTALLATION
Issue 1, Apr 1982
INTERNAL TELEPHONE SYSTEM NO. 3
3 TECHNICAL DESCRIPTION
4 SYSTEM OPERATION
6 TERMINAL EQUIPMENT
7 EQUIPMENT PROVISION
9 ANTI STATIC PRECAUTIONS
The Internal Telephone System No. 3 (ITS 3) started life in 1977 as a Factories Department
student project to look into the feasibility of a British Telecom produced internal
telephone system to extend the existing internal telephone system (ITS 2). It will be
marketed as PROTEUS.
PROTEUS will only accept Loop Disconnect Pluses and is compatible with telephone
instruments employing this type of signalling. Battery driven key-pads should not
generally be used.
PROTEUS may be provided with a maximum capacity of 24 or 64 extensions. The system will
be known as PROTEUS 24 and PROTEUS 64. PROTEUS 24 is the same physical size as PROTEUS 64
but is only wired to a maximum of 24 extensions.
The system is based on a Central Switching Unit (CSU) which utilises CMOS solid state
technology. The CSU for both system sizes measures 472 mm wide 276 mm high 353 mm deep.
The 24 way system weighs 25 Kgs and the 64 way system weighs 26 Kgs fully equipped. The
CSU is free-standing (on a desk or table supplied by the customer). Growth to each system
is achieved by the provision of additional Apparatus Slide-in Units, (ASU's) see paragraph
3. UP to three cords (depending upon the number of extensions provided) connect the CSU to
a Box Connection. Extensions are radially wired from the Box Connections using a single
pair of wires. The numbering range due to technical reasons is as follows:-
00-07, 10-17, 20-27, 30-37, 40-47, 50-57, 60-67, and 70-77
3 TECHNICAL DESCRIPTION
PROTEUS is a single wire switched system making extensive use of CMOS logic circuitry for
control and switching functions. Line balance conditions are achieved by unbalanced to
balanced line transformers. The system is based on the use of single time shared data
highways for each of the required system conditions; such as phone busy or number
unobtainable. Conditions on any one highway associated with a particular line condition
depend on the address present on the telephone address bus and the current status of that
The crosspoints used in PROTEUS are CMOS analogue switches namely the CD 4051 which is
a single 8-channel multiplexer-demultiplexer i.e. an 8 x 1 switch.
These are arranged to form the basic switching array of an 8 x 8 matrix. Thus any
extension can feed onto any one of the 8 available interconnect circuits. Expansion to the
maximum system size of 64 extension is achieved by adding additional 8 x 8 arrays.
The modules/ASUs used in PROTEUS are as follows:-
(a) Power Supply Unit (PSU) -One required for a system. Mains Powered, capable of
supplying a fully equipped system.
(b) Line Extension Module - One required for each 8 extensions provided. Consists of a
mother/ daughter ASU which houses the basic 8 x 8 switching array and the line interface
for 8 extensions.
(c) Common Control ASU One per system. Provides timing and control of system. Generates
all tones required i.e. dial, busy, NU, and ring.
(d) Call Connect Circuit One per 2 connect circuits required. (Dialler) ASU Connects
calls required onto connect circuit. Contains numbers dialled register.
4 SYSTEM OPERATION
When the exchange is idle the busy line from the line interface is continuously monitored
until a phone busy condition is present.
When this busy condition occurs the crosspoint switch monitor line is interrogated to
determine whether the particular extension has already been allocated a speech path, if
not, a call connect circuit with its associated transmission path is allocated by the
common control card to that line and dial tone is returned to the caller.
When the caller dials, the number dialled is entered into a register in the call
connect circuit via the common Loop/Dis highway. The call connect circuit then monitors
the busy and number unobtainable lines during the address of the required number, and if
either are active returns the appropriate tone to the caller, if not then the ring current
generator is enabled and the called number rings. If the ringing telephone is answered the
ring current generator is cleared, the speech path enabled and the connect circuit cleared
ready for conference dialling.
5.1.1 All extensions will be able to dial every other extension on the system.
5.1.2 All two-way calls are secure against intrusion.
5.2.1 This facility enables up to 6 extensions to be linked by the same speech channel
making it possible for all to be able to speak and listen.
This facility is available to all extensions.
5.2.3 It is possible to "call in" or "drop out" conferees without
disrupting the call.
5.2.4 The facility remains under the control of the conference convenor
5.2.5 If any extension called into conference is not answered within 12 seconds the
connection to that particular station is forced released. Equally if the called extension
is engaged the connection is forced released after 4 seconds.
5.2.6 The conference calls are secure against intrusion.
5.3 Incoming Calls Barred
5.3.1 Any extension can be connected to this facility and any extension calling a
"Barred" extension receives NU tone.
5.4 First Part Release
5.4.1 All extensions whether they are in two-way conversation, or are called into
conference have the First Party Release facility.
6 TERMINAL EQUIPMENT
All 700 type telephones
Press-Button Keyphone. Battery driven key-pads should not generally be used
Compact or Jubilee Telephones, and any Special Range Telephone (subject to the limitations
of that SRT)
All LSTs including DORIC-HARMONY. Plans 1, 1A, and 4
Any add-on terminal equipment, e.g. Handsets 4 and 7 Speakerset etc.
7 EQUIPMENT PROVISION
Basic Equipment All systems will comprise the following basic
- Case 246A 24 way (fully wired equipment cubicle) (ITEM CODE 435995)
- Case 246B 64 way (fully wired equipment cubicle) (ITEM CODE 435996)
- Power Unit No. 155A (ITEM CODE 314364) - To be requisition separately :- Plugs for
Socket Outlets No. 103.
- Cable Connection 14A (ITEM CODE 435997) - Up to three cords may be required depending
upon the number of extensions to be provided (see paragraph 8.2).
- Call Connect Circuit ASU/1Al/FDH 16900 (ITEM CODE 418052)
- Line Extension Circuit ASU/1Al/FDH 16894 (ITEM CODE 418052.)
- Common Control ASU/1A1/FDH 16891 (ITEM CODE 418054)
Provision of ASUs Call Connect and Line Interface Circuits are provided in accordance
with the Advice Notes issued.
The ASU's necessary to meet these requirements are shown below:-
Line Extension cct - system max = 8 - circuits per card = 8 (item code 418053)
Call Connect cct - system max = 4 - circuits per card = 2 (item code 418052)
- 2 Conn ccts up to 16 Extns
- 4 Conn ccts up to 32 Extns
- 6 Conn ccts up to 48 Extns
- 8 Conn ccts up to 64 Extns
8.1 A set of diagrams will have to be requisitioned and left on site. They should be
ordered in accordance with TI K5 A040l.
The diagrams are as follows:
FDH 16900 Call Connect Circuit
FDH 16894 Line Extension Circuit
FDH 16891 Common Control Circuit
8.2 The CSU should be desk or table mounted, preferably in an office environment.
Service access to the front of the unit should be unrestricted. The mains lead and the
line cords are fed from the rear of the unit and will have a free length of 3 metres,
measured from the rear of the unit. It is therefore essential that the Box Connection to
which the cords will be terminated is located within this limit. Care should be taken that
these cords do not cause a safety hazard. The customer must provide a SWITCHED 13 amp
socket outlet in a position conveniently close to the equipment for the SOLE use of
8.3 The line cords will be terminated at one end to a plug 226. Although the line cord
is described as a cord it is in fact a cable of 3.5 metres in length, the extra 0.5 metres
of cable is to allow the cable to be stripped and terminated on a suitable box connection
(see wiring chart).
At the rear of the CSU there are three 226 sockets which are numbered right to left
PL1, PL2 and PL3. Each socket is allocated a number of extensions and are wired to number
from top to bottom.
PL1 is allocated extensions 00-07, 10-17, 20-27. PL2 is allocated extensions 30-37,
40-47, 50-57. PL3 is allocated extensions 60-67, 70-77.
Each plug connected to the cord will have to be signwritten PL1, PL2 or PL3 and plugged
into the appropriate socket.
8.4 Remove the front and rear panels from the CSU and insert the power module from the
front securing it with the single screw from the back. The power cord will be terminated
to a Plugs for Socket Outlets 103 fused at 3 amps.
8.5 The ASUs can now be inserted into their appropriate positions (see poster diagram
on reverse of front cover). (See also annex A.)
Before inserting the ASUs care should be taken to ensure the busying switches for the
Connect Circuit units, the (Connect Circuit busy switches will be found on the Common
Control unit) and the incoming calls barred switches on the Line Interface units are in
the normal position. Fig 1 shows a bank of switches as mounted on a Line Interface ASU.
Switch 1 and 2 are operated, 3-8 are in the normal position. (Note the busying switches on
the Call Connect circuits are opposite in operation to the Line Interface circuits e.g. to
busy a Call Connect circuit operate the switch to the operated -position
The Line Interface ASUs are inserted into card guide numbers 36-81. They are identified
by the Blue extraction handles on the card. One Line Interface ASU caters for 8
extensions. The maximum number of extensions is 64.
The Connect Circuit ASUs are inserted into card guide numbers 21. 24, 27 and 30. They
are identified by the Yellow extraction handles on the card. One Connect Circuit unit
caters for 2 circuits. The maximum number of connect circuits is 8.
The Common Control ASU is inserted into card guide number 33. It is identified by the
Red extraction handle on the card. There is one Common Control unit for the system.
9 ANTI STATIC PRECAUTIONS
As Electrostatic Sensitive Devices i.e. CMOS are used in the CSU, the normal precaution
should be taken by personnel to discharge any body charge by occasionally touching earth.
Handle all ASUs by the handle provided and avoid bodily contact with circuit track and
components wherever possible and anti static bags should be used when transporting ASU's.
NOTE: It is hazardous for personnel to be earthed while working on live equipment,
so on no account should staff be connected to earth, unless the approved high resistance
to earth wrist-straps are employed.
10.1 When the power is switched on the LED on the common control unit should flash to
indicate it is functioning correctly.
10.2 Using d test telephone on an extension which is terminated at the distribution
point, seize each connect circuit in turn by taking the test telephone 'off hook' and
ascertain that dial tone is received. The first connect circuit to be seized is the top
circuit on the first ASU in card guide number 21. On seizure the LED associated with the
circuit will glow and dial tone is received. If the test is satisfactory replace the test
telephone and busy the circuit by operating Switch SA1 which is mounted on the Common
To test the next connect circuit lift test telephone 'off hook' and this should seize
the top circuit on the second ASU and the associated LED will glow. If the test is
satisfactory replace telephone and busy the circuit by operating switch SA3.
Test the remaining fitted connect circuits in sequence in the same manner. The connect
circuits are seized in the following order:- 1, 3, 5, 7, 2, 4, 6 and 8.
Switches SA1-SA8 will busy the Connect Circuits. On completion of testing restore all
the busying switches to normal.
10.3 Using the test telephone and another telephone on an extension generate a call on
each of the connect circuits, busying each connect circuit in turn as in paragraph 10.2.
10.4 Using the test telephone generate a call to a busy extension on each connect
circuit to ascertain busy tone is received.
10.5 Using the test telephone generate a call to a spare extension on each connect
circuit to ascertain NU is received.
10.6 Using the test telephone generate a call to another extension and ascertain the
'First Party Release' feature on each connect circuit.
10.7 Using the test telephone and various other extensions set up a conference up to
the maximum of 6 extensions. The extension convening the conference dials the extension of
the first conferee and establishes the connection, requests the conferee to hold whilst
the next conferee is dialled, no dial tone is received. This procedure is then continued
for further conferees.
Whilst in the conference mode, call an engaged extension and ascertain that busy tone
"times out" after approx. 4 seconds. Call a free extension but do not answer the
call and ascertain that the ringing tone "times out" after approx. 12 seconds. A
conference and the subsequent tests should be carried out on each connect circuit.