All the information below is taken from the GPO
Technical Instructions XXIII (1930).
| Type |
N.T. Number |
Capacity
Extensions |
Equipment
Extensions |
| W.P., S.C. |
1 |
5 |
3 |
| W.P., S.C. |
2 |
5 |
5 |
| W.P., S.C. |
3 |
10 |
10 |
| W.P., S.C. |
5 |
16 |
16 |
| W.P., S.C. |
6 |
20 |
20 |
| W.P., S.C. |
7 |
30 |
30 |
 |
 |
| Switchboard W.P., S.C. NT No. 1 (Picture
dated 1924) |
Switchboard W.P., S.C. NT No. 2 (Picture
dated 1924) |
| |
|
 |
 |
| Switchboard W.P., S.C. NT No. 6 (Picture
dated 1924) |
Switchboard W.P., S.C. NT No. 7 (Picture
dated 1924) |
Transmission Data
The allowance for the losses in the switchboard apparatus on an exchange to
extension connection is 0.5db, or when calling in facilities are provided
1.2 db.
Design
These switchboards are designed for fixing to a wall or other flat vertical
surface. Wiring may be led in from either side through holes provided
in the backboard. The terminals are fixed to the backboard and
protected by a cover which is hinged on the left. The front portion of
the board carries all the apparatus and is hinged on the left to give access
to the interior.
Operating Facilities
Each line is connected to an indicator, jack and plug; the indicator (1000
ohms) acts as a calling signal and as a ring-off signal.
When working to a non-condensered magneto exchange the operator's
telephone is connected to a plug only and connection with any circuit is
obtained by inserting the telephone plug into the jack of the desired line.
When working without calling-in facilities to a condensered magneto
exchange or to a C.B. exchange, the operator's telephone is also connected
to a jack. The generator connections are arranged to ring out on the
plug only and, if the plug of a calling line is inserted into the telephone
jack, any required line may be rung through the plug without disconnecting
the calling line. This method of operating is adopted to avoid giving
false clears while setting up an exchange connection, and a holding jack is
also provided for use in the same circumstances when, for any reason, it is
necessary to leave an uncompleted connection.
For working to a condensered magneto exchange or to a C.B. exchange, the
above arrangements are departed from in detail when calling-in facilities
are provided, particulars of the modifications are given on Diagrams T.L.
969 (N. 917) and T.L. 971 (N. 919).
Night Service
The standard diagrams allow for any extension to be connected to any
exchange line for direct night service.
Calling-in Facilities
For the mounting of the eye-ball indicators necessary for the receipt of
calling-in signals a "Case Indicator Mounting" should be fitted. The
case is a standard item and, for single-cord switchboards, is provided in
three sizes designed for fitting in the place of the terminal cover.
The details are as follows:-
| Case-Indicator No. |
For use on Switchboards |
Capacity (inds) |
Height (in) |
Width (in) |
Depth (in) |
| 3 |
W.P., S.C., N.T. 3 |
4 |
3.2 |
10.25 |
6 |
| 4 |
W.P., S.C., N.T. 5 and 6 |
6 |
3.2 |
16 |
6 |
| 5 |
W.P., S.C., N.T. 7 |
6 |
3.2 |
23 |
6 |
Where 7- or 8-point jacks are necessary for the exchange lines, single
jacks (Rate Book description "Jack, Switchboard, N.T. 12") should be fitted
in the woodwork below the jack field. Wiring should be transferred to
these jacks from those in the bottom strip and the disused jacks pegged up.
The remainder of the special apparatus should be mounted in a convenient
manner apart from the switchboard.
Operator s Telephone
The standard operator's telephone to be used with this type of switchboard
is a "Telephone, No. 59" which includes a hand micro-telephone. When a
breast-plate transmitter and head-gear receiver are required they should be
wired to Figures 6 and 7, Diagram C.B. 1208 (N 960).
Night Alarm
A bell and switch is
included in the equipment of the switchboard.
Cord Test
The "Hold" jack should also be used for cord testing. Switchboards
No's 5, 6 and 7 are fully equipped in this respect when issued.
|