TELECOMMUNICATIONS INSTRUCTION
C MARKETING - INSTALLATION
3 INTERNAL
M 4001
Issue 1 (September 1971)
HOUSE TELEPHONE SYSTEM No. 2
Description, Installation and Maintenance
General
This
Instruction describes the House Telephone System No. 2. The telephone instruments are coded
in the 500 series and are similar in appearance to the Telephone No. 706, except that the dial
is replaced by a push-button unit. House telephones of the 100 series (see Q 3950) cannot
be interconnected with 500 series House Telephones.
Facilities
The House Telephone System No. 2 provides intercommunication between two or more locations
(16 stations maximum) without secrecy. Access to exchange lines cannot be given, and the
whole system must be housed in one premises. Several conversations may be conducted at the
same time and conference calls may be established between an number of stations.
Description
Table and wall instruments are available having 5, 10, and 15 push-buttons, these are
suitable for up to 6, 1 1 and 16 stations respectively. A multiple cable corrects the
instruments together and the 10v dc required for operating the system is obtained from a
Power-unit No. 53A. The table and wall instruments cannot be converted from one to another.
All table telephones are supplied with line cords but not with terminal blocks.
Wall mounted instruments are not supplied with line cords and should always be cabled
direct. The telephone instruments are fitted with Handsets No. 3 but to ensure operation of
the spring-sets an additional weight (Part 1/DWE/7) is fitted.
The wall variants can have the handset temporarily placed, on the handset
rest, in an "Off Hook" position.

There are two diagrams in the Q series for the system:-
Q 361 Shows telephone instrument and wiring of instrument to terminal block.
Q 362 Shows cabling of system and explanatory diagram.
Method of operation
Each
calling button has a 'normal press' and an 'overpress' position. After lifting the
handset, the required station calling button is depressed to its full extent. This
operates the buzzer at the called station. When pressure is released the button restores
to the 'normal press' speaking position. At the conclusion of a call, replacing the
handset will release any operated calling buttons.
Conference calls may be established between any number of stations. The initiating caller
must call each required station in turn. The called party must then depress the calling
button appropriate to the initiating station.
Numbering of stations
Stations should normally be numbered in sequence according to their position in the
multiple cable. If, however, the subscriber has any specific station arrangement, stations
may be numbered and wired in any order, but the most economical cable run should be
followed. A directory card is supplied with each instrument, enabling each station to be
associated with a person's name. It should be noted that when installations consist of 6,
11 or 16 stations, the additional station is called by utilising at each station the spare
button corresponding to that particular station number. if the subscriber wishes he may
unclip the calling button cover and remove the numbers provided, replacing them with a
designation label to suit his own requirements.
Installation
Table 1 shows the types of telephone instruments together with the number of stations that
can be accommodated and the cable required. If, at the time of installation, there is the
probability that the system may require extending at some future date, a larger cable
should be fitted initially.
TABLE 1
Number of Stations
|
Telephone House
No.....
|
Type
|
Wiring Size
|
6
|
500
|
Table
|
21 wire
|
6
|
501
|
Wall
|
21 wire
|
11
|
502
|
Table
|
24 wire
|
11
|
503
|
Wall
|
24 wire
|
16
|
504
|
Table
|
41 wire
|
16
|
505
|
Wall
|
41 wire
|
Siting of telephone instruments
Very damp or dusty situations are unsuitable for House Telephone Systems.
Cabling limits
The maximum cable length between the two extreme stations is 600 yards for 5 and 15 button
instruments. This will be reduced to 300 yards if one or more stations has an extension
caller fitted. The 10-button instrument is limited to a maximum cable length of 500 yards,
or 200 yards if extension callers are used. This can be increased to 600 yards 300 yards
respectively, by running an additional 2-wire cable connected in parallel with the power
pair in the main cable.
Extension callers
In addition to the buzzer in the instrument either a Bell No. 56A or Buzzer No. 20B can be
fitted as an extension caller, the choice being left to the subscriber. In each case the
coils should be connected in series.
Maintenance
The following individual items are replaceable:-
Transmitter-inset No. 13C or No. 16.
Receiver-inset No 4T.
Handset No. 3.
Weight, Part I/DWE/7.
Cord, Instrument No. 1. 4/88AK, ..., 10 in.
Should any other components require replacement, then the entire instrument must be
replaced.
Power supplies
The House Telephone System No. 2 is designed to operate from a 10v dc supply derived from
a Power Unit No. 53A. If possible, the power unit should be located near the centre of the
system rather than at one end, and should be connected to the system as shown on Diagram Q
362.
Introduced circa 1967.
 |
Close up of press buttons. The clear
plastic covers are removable to allow the installer to change
the numbers. The numbers are paper. |
|
 |
Wall mounted version |
|