PLAN NUMBER WORKING
These telephones are for providing economically various extension schemes without the use of separate switches or switchboards.
They are arranged to accommodate key units having from one to nine spring sets of the make-before-break change-over type, i.e., "K" combination. The spring sets are operated by push buttons, and are illustrated below.
For a simple extension or for recalling a P.B.X. operator the instrument N1003 type has a key unit with one set of K springs.
For other extension schemes the key units have a number of K spring sets, the standards being for 4 and 9 sets. The push buttons on a telephone with a 4K spring set operate respectively (left to right) 2K - 1K - 1K spring sets, while with a 9K set, 4K - 1K - 4K are operated.
Each contact spring is wired to a separate terminal so that the scheme in hand may be readily connected up.
On the 4K and 9K key units there is a mechanism which can be varied to control the non-lock or locking of the two outer keys, the centre key being non-locking. There is also supplied with each of these key units a T piece which is fixed to the cradle lever when the extension plan necessitates the release of a key on replacement of the micro-telephone.
Instruments are also available with battery bells so that plans to suit almost any requirement can be arranged.
The telephones are normally produced in black, but if specially ordered,
they can be supplied in Chinese Red, Ivory or Jade Green. They can also be obtained
without the instruction tray and directory pad fitment.
For telephones with two or three push buttons the key unit required must be stated.
In the case of plans requiring only two push buttons, chromium finished dummies can be supplied for the third hole.
The terminal blocks, cords and labels vary according to the plan required, so that full details regarding the scheme to be operated should be supplied when ordering.
Circuit diagrams of various plans can be supplied on request.
Overall dimensions 9.25 x 8.5 x 6 inches.
Maximum weight 6 lb. 8 oz.
The instruments in the table below may be complete with instruction tray fitment.
Many variations were made for the world and home markets.
N1003 introduced around 1938.
N1003H16 has a single button marked "Automatic". Diagram N70721 is dated 1946.
N1004H models have two buttons marked "Call Back" and "Release".
Most of the N1005 models and some N1004 models were standard telephones ready to accept a three or two button switch unit, as required.
The `A' variant had rollers on the gravity switch hooks, whilst the `B' variant onwards had a flat plate to operate the switch hooks.
See N1366 for CB types
Note - Wall telephones for Plan Number working can also be supplied.
Last revised: August 02, 2022