House Telephone Systems are just intercom systems.
There is no connection to an exchange line. Systems were powered originally
by batteries, but today small power units have taken their place. Due to
the miniaturisation and lower cost of automatic telephone systems (PABX), HTS/intercom
systems are virtually non-existent today.
BT House/Internal Telephone Systems (HTS/ITS) had no connection to the BT Network and
were installed as intercom systems within customers premises, typically in large
supermarkets. The range comprises:-
HTS No.1 - Press button telephone intercom system with table or
wall mounted telephones (similar in appearance to 300 type instruments) with 5, 10 or 15
buttons depending on system size, maximum system size is 15 stations. The telephones are
interconnected by multi-pair cabling (12 wire for 5 station systems, 21 wire for 10 or 15
station systems) and locally powered by dry batteries.
HTS No.2 - Press button telephone intercom system with table or
wall mounted telephones (similar in appearance to 706 type instruments) with 5, 10 or 15
buttons depending on system size, maximum system size is 16 stations. The telephones are
interconnected by multi-pair cabling (21 wire for 6 stations, 24 wire for 11 stations and
41 wire for 16 stations) and powered by a mains Power Unit 53.
ITS No.3 (PROTEUS 24 and 64) - Standard type 'Dial' or 'Press
Button' LD signalling telephones connected to a free standing self-contained Central
Control Unit (CCU) containing electronic switching and control circuitry. Was marketed
under the name of Proteus. The telephones are 2-wire connected to the CCU via twisted pair
cabling. Maximum capacities 24 or 64 stations depending on type of backplane and line
interface equippage. The system is mains powered by a Power Unit 155A contained within the
HTS No. 1 was introduced in 1959 and made obsolescent in October 1973. HTS No. 2 was
introduced in 1967 and ITS No. 3 in 1982.
It was intended to withdraw all HTS/ITS by September 1992 and all identified customers
were contacted by sales groups to encourage change out for a modern system.
HTS/ITS do not have a telephone number and so it has become the practice to issue a
'Private Circuit' number for fault reporting or billing purposes on HTS 1 and 2 systems,
ITS No 3 (Proteus) should have been recorded on CSS.
In practice many customers were not aware of these private circuit numbers for reporting
faults or even realising that they are BT maintained systems resulting in faults not being
The ITS was manufactured for BT/GPO/Post Office by various companies, only the ITS No.3
CCU was manufactured by BT Fulcrum.
All systems were rented
None as ITS systems are not network connected and hence not subject to the Approval
M&S Circular 214/91 'Withdrawal of Internal Telephone Systems & Proteus.
HTS No. 1 - Diagrams Q 351,352 & 353. TIs C3M 4000, E5D 7301.
HTS No. 2 - Diagrams Q 361 & 362. TIs C3M 4001, E5D 7302.
ITS No. 3 - Customer Apparatus Guide Notes 'Proteus 24 & 64' (Site documentation
supplied with system), TIs C3M 4010 & ESD 7302.
ITS No. 3 CCU contains static sensitive CMOS components, precautions must be taken to
prevent static damage.
The above was taken from BT documentation
Description BT Item Code
HTS No 1:-
Telephone House 100, (5 stations -table model) 42 1902
Telephone House 101, (5 stations -wall model) 42 2034
Telephone House 102, (10 stations -table model) 42 1903
Telephone House 103, (10 stations -wall model) 42 2035
Telephone House 104, (15 stations -table model) 42 1904
Telephone House 105, (15 stations -wall model) 42 2036
HTS No 2:-
Telephone House 500, (5 stations -table model) 42 0153
Telephone House 501, (5 stations -wall model) 41 0192
Telephone House 502, (10 stations -table model) 41 0154
Telephone House 503, (10 stations -wall model) 41 0155
Telephone House 504, (15 stations -table model) 41 0156
Telephone House 505, (15 stations -wall model) 41 0193
Power Unit 53B 31 4065
ITS No 3:-
Proteus Power Unit 155A 43 200#
Proteus Case 246 A 43 201#
Proteus Case 246 B 43 202#
Proteus Card 1A1/FDH 16891 (Red Handle) 43 203#
Proteus Card 1A1/FDH 16900 (Yellow Handle) 43 204#
Proteus Card 1A1/FDH 10894 (Blue Handle) 43 206#
Proteus Card Common Control PCB 43 209#
Fuses 3 Amp, 500 mA, 1 Amp (spares supplied with CCU)
BT Repair Services (Formerly Fulcrum) Item Code numbers.