Post Office N-diagrams
Post Office N-diagrams
| N000 up | Diagrams from N000 to N999 |
| N1000 up | Diagrams from N1000 to N1999 |
| N2000 up | Diagrams from N2000 to N2999 |
| N3000 up | Diagrams from N3000 to N3999 |
| N4000 up | Diagrams from N4000 to N4999 |
| N5000 up | Diagrams from N5000 to N5999 & 8000 to 8999 |
| Numerical listing | Listing with titles in numerical order |
All of the diagrams are in Adobe Acrobat® Portable Document Format (PDF). To download the free reader go to the Acrobat Web site
These diagrams were used by Post Office technicians when installing or servicing instruments and small systems. The full range of subscriber's apparatus was covered. This is invaluable information for collectors wishing to restore items to working order.
N-diagrams must have been in use from a very early date in the 20th century, but they appear to have been regularised in 1917. The very early ones had a diagram on the front face and a typed description on the reverse. Later ones were entirely hand-lettered. First editions had no revision letter: subsequent editions had revision A, B, C, and so on marked in a box on the LH edge of the first sheet.
Originally, I scanned only the diagrams in my collection that struck me as being useful to collectors. Due to considerations of space I confined the original batch of diagrams to these. However I have made good progress on scanning many of the remaining diagrams in my collection and they may appear as the scans are completed. The Numerical Index lists all the diagrams. The unscanned ones are highlighted in yellow. Occasionally I have received requests for other diagrams not so far scanned and I have scanned these more or less on demand. If you have an N-diagram in your collection that I haven't got, I would be very grateful for a scanned copy, photocopy or loan of it to help complete the collection.
The following are broad guides to the content of the various ranges of numbers. Itis not comprehensive and there are odd quirky items in the middle of ranges.
N001 is an Alphabetical List of Diagrams for Subscriber's Apparatus. N002 a list of PABX diagrams, N003 a list of PMBX diagrams N005 is a list of Bell sets.
Telephones are described on the N-diagram 100 greater than the number of the telephone. Eg Telephone No 706 is described in N806. Hence the series N100 to N499 covers telephones. Bell sets are described in N-diagram 500 greater than the Bell Set number. Eg Bell set No 26 is described in N526. Also in the 500 series are a number of dials. The 600 series contains power units and rectifier with no clear linkage to the type number. The 700 series is mostly concerned with switchboard termination. The 800 and 900 series are telephones once again.
The 1000 series contains diagrams for various subscriber's extension plans.
The 2000 series contains switchboard connections, autosenders, call office circuits, and some plan diagrams. Quite a mish-mash really.
The 3000 series are mostly concerned with shared service working.
The call office theme is continued in the 4000s up to the 4200s. There is more plan working in the 4300s. The 4400s have some curiousities and a number of amplified telephones. More plan working and call offices in the 4600s. The 4900 series is for the Special Range of Telephones.
The 5000 series includes some subscriber's carrier equipment and the 8000 series completes the set with the newer plug-ended telephones.
I have only placed the latest available revision on the web site. Sometimes I have earlier revisions which may be of historical interest. Ask me me if you need something.
The diagrams were supplied by the Post Office to the British Railways Board, who ran their own internal telephone system. With the liberalisation of customer premises equipment most of the old Post Office equipment became obsolescent and production of N-Diagrams stopped. As a space saving exercise the collection was about to be consigned to the waste bin and so I rescued it.
Fellow THG member Laurence Rudolf has kindly scanned a large number of early N-diagrams in his collection. Thanks, Laurence.
The later ones were in a 1930s GPO folder with George VI crown. The collection includes some diagrams in several different revisions which have been included for completeness and historical interest. Quite a few are very early diagrams, pre-1917, some are undated, most of which came from a small bound book the same size as an N-Diagram. The Red book has the Lion & Unicorn emblem on the cover and the book is titled "Telephone Diagrams". The first page. "For Official use, Post office Telegraphs. Connections of Telephonic Apparatus and Circuits. General Post Office 1909.Price One Shilling and Threepence." This was the fore runner to N-Diagrams. It turns up for sale from time to time at THG swapmeets.
Another THG member, David Roberts, G7MYM, has helped considerably by scanning part of his collection for us. The diagrams relating to plan working in the 4500 and 4600 range are thanks to David, as are the subscriber carrier diagrams in the 5000 series. David has also done most of the work on the numerical listing for which I am very grateful.
I also gratefully acknowledge additional contributions from Peter Duffield and Andrew Emmerson, Kevin Dodman, Ron Sewell, John Goldfinch and Jim Foster.
I have scanned these diagrams at 300 dots per inch and stored them in Adobe Acrobat® Portable Document Format. They are reproduced actual size - which varies according to age. The older diagrams are about 179 x 108 mm and the later ones are either A5 (149 x 210 mm) or A4 (210 x 297 mm). They were printed on fairly cheap paper, some pink, some yellow and mostly white (well fairly white). The printing was presumably offset litho and the ink wasn't very black on some of them. The printing is not always straight on the page (honest, I DID put them on the scanner square).
The task of indexing all of them is formiddable. So please excuse the fact that you get am FTP-style list of the files, which can be generated automatically. The Numerical Index has been updated to include all diagrams in my collection, with highlights of the ones which have not been scanned yet. However, there are now links to the relevant diagrams from the pages on Bob Freshwater's Telephone Files site.
[Sam Hallas, updated April 2008]
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