DIAGRAM INFORMATION

This is a large subject and this is a condensed description of the diagram system.

For telephone diagrams go the the BPO telephone list, click on the telephone or equipment of your choice - if a diagram is available then it will be linked from the page you chose. If not, then make a note of the diagram number and go to the Sam Hallas web site (most GPO telephones are prefixed with one and adding 100 to the telephone number generally gives you the diagram i.e. Telephone 746 = N846).

BPO diagrams and drawings are either numbered or numbered with a lettered prefix. The prefix on diagrams may be one or two letters of the alphabet and those with A, F, K, M, P, Q, S, U, W or X as the third letter of the prefix code take the same number of the associated circuit diagram. The letters have the following significance:-

A - Apparatus or equipment
F - Floor plan
K - Trunking
M - Maintenance
P - Assembly
Q - Stock lists
S - Circuit
U - Shelf jack wiring or U link connections (J or SA series)
W - Wiring or routed circuit wiring
X - Cross-connection

In addition to the above, joint circuit and wiring diagrams are given the basic and wiring codes, e.g. RP/RPW

Drawings are numbered in the range 60000 - 99999

Diagrams in general use are:-
General Wiring Diagrams are prefixed with SA
Wiring Diagrams that show wiring runs and wire colours are prefixed with SAW
Police apparatus diagrams are prefixed with PA
Fire alarm wiring diagrams are prefixed with FA
House Exchange systems are prefixed with Q
Testing diagrams are prefixed with T
Telephone wiring diagrams are prefixed with N
Telegraph theoretical diagrams are prefixed with TG
Telegraph wiring diagrams are prefixed with TGW

List of all Diagram types:-

Prefix Code	Description	Remarks
1 to 500 399	Fully dimensioned drawings of apps and equip approved for production
AD	Air Defence drawings and diagrams
ADA	Air Defence drawings and diagrams
ADF	Air Defence drawings and diagrams
ADK	Air Defence drawings and diagrams
ADL	Air Defence drawings and diagrams of cable networks	was ROC
ADP	Air Defence diagrams
ADU	Air Defence diagrams
ADW	Air Defence diagrams
ADX	Air Defence diagrams
AGS	UAX No. 7 diagrams
AS	Area of search plans for Repeater stations
AT	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts	Schematic
AT/ATW	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts
ATM	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts
ATU	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts	Shelf, jack and U points
ATW	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts	Wiring - shows routing and colours
ATX	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts	cross connection
AU	Auto exchange ccts; wholly or partially electronic; trunk toll; misc ccts
BB	Broadband utilization
BM	Cable and network diagrams
C	Cable and network diagrams that are security classified
CB	CB exchange ccts
CBU	CB exchange ccts
CBW	CB exchange ccts
CBX	CB exchange ccts
CU	CB exchange ccts
CBS	CBS exchange ccts
CBSU	CBS exchange ccts
CBSW	CBS exchange ccts
CBSX	CBS exchange ccts
CBU	CBS exchange ccts
CBW	CBS exchange ccts
CBX	CBS exchange ccts
CC	Communication charts	Regional
CCS(L)	Cable cross section diagrams
CD	Contour drawings insufficiently dimensioned for inclusion in main series
CN	External plant and protection
CSU	CBS exchange ccts
CTS	Drawings, diagrams etc for training branch
CU
CV	Valve characteristic curves
CX
D	Boundary maps, key plans and cable network diagrams covering the whole country
DL	Drawing lists for selected jobs
DR	Drilling for apparatus
DT	Data transmission and associated equipment
DTN	Telegraph defence ccts and accommodation plans
DTW	Data transmission and associated equipment
DT/DTW	Data transmission and associated equipment
DWL	Data transmission and associated equipment
E	Diagrams of non-STD transmission equipment and early equipment
EC	Installation particulars of equipment
ECW	Installation particulars of equipment
ED	Drawings of Transmission equipment
EDA	Drawings of Transmission equipment
EG	Drawings and diagrams for electronic exchanges
EGA	Drawings for electronic exchanges
EGC	Diagrams developed under the auspices of the JERC
EGF	Diagrams developed under the auspices of the JERC
EGN	Diagrams developed under the auspices of the JERC
EGU	Diagrams developed under the auspices of the JERC
EGX	Diagrams developed under the auspices of the JERC
EQ	Semi-auto equipment fire emergency ccts
ER	Semi-auto equipment fire emergency ccts
ES	Accommodation and equipment layout plans of buildings	was EX SK series
ETC	Drawings, diagrams etc for training branch	was CTS series
ETE	Drawings and diagrams of Radio stations, Tele Exchs & Telegraph layouts
EW	Non-standard transmission equipment
E/EW	Non-standard transmission equipment
EX	Drawings and diagrams for all divisions in research branch, except R12
EX/SK	Superseded by ES series
F	Main cable development forecast diagrams
FA	Fire alarm ccts
FA(L)	Fire alarm ccts
FAW	Fire alarm ccts
FDA	Drawings for factory divisions
FDH	Drawings for factory divisions
FY	Drawings for factory divisions
GMT	Clocks and Greenwich mean time cct
GMTW	Clocks and Greenwich mean time cct
HF	HF diagrams
IF	Factory diagrams
LA	Circuit lab diagrams
LD	Label diagrams for pasting into instruments
LFS	Factory drawings
LL	Drawings of local line network
LR	Misc drawings and diagrams
MISC
MOH	Drawings of items provided for the department of health
MS	Experimental and temporary ccts
MSU	Experimental and temporary ccts
MSW	Experimental and temporary ccts
MSX	Experimental and temporary ccts
MT	Vehicles and associated equipment
MTF	Methods for fitting items on vehicles for M Branch
MU	Main underground HF and carrier cables, land end and sea earth cables
MU-FM	Main underground HF and carrier cables, land end and sea earth cables
MU-TT	Test tablet diagrams. Suffix TT added to associated MU number
MU4000(HF)	Main network diagrams, motorway cables layout diagrams
MW	Main network diagrams, motorway cables layout diagrams
N	Telephone, Call offices and pbx ccts	loose leaf circuit diagrams with wiring details
ND	Network diagrams of private ccts
NT/NTA	Ex National Telephone Company
PA	Police alarm ccts
PA(L)	Police alarm ccts	loose leaf
PF	Phonogram and tele/telegraph ccts and installations
PFU	Phonogram and tele/telegraph ccts and installations
PFW	Phonogram and tele/telegraph ccts and installations
PFX	Phonogram and tele/telegraph ccts and installations
PLAN	Miscellaneous diagrams, maps, networks and proposals
P/DC	Telecoms power plant ccts
P/DCW	Telecoms power plant ccts
P/EL	Electric light fittings
P/ELD	Illumination intensity
P/HG	Heating layouts. Boiler room and fuel hopper arrangements
P/LG
P/MSC	Miscellaneous
P/P	Engine room, switch gear wiring diagrams
P/PN	Pneumatic diagrams
P/TC	Power plant drawings
P/VN	Ventilation layouts
Q	House exchange telephone systems	loose leaf
Q(L)	House exchange telephone systems	loose leaf
R	Master copies of tracings from blanks, illustrations for books etc
RA	Relay adjustment cards
RES	Drawings and diagrams for all divisions in research branch
RP	Repeater and amplifier equipment and ccts
RPA	Repeater and amplifier equipment and ccts
RPW	Repeater and amplifier equipment and ccts
RPX	Repeater and amplifier equipment and ccts
ROC	NOW ADL
RSF	Repeater station distribution frame layouts
RSS	Repeater station distribution frame layouts
RT	Automatic exchange routiner ccts
RTM	Automatic exchange routiner ccts
RTU	Automatic exchange routiner ccts
RTW	Automatic exchange routiner ccts
RTX	Automatic exchange routiner ccts
RW	Automatic exchange routiner ccts
S	Parts and composite parts of common use
SA	Circuits of telephone subscribers apparatus
SA(L)	Circuits of telephone subscribers apparatus
SA/SAW	Circuits of telephone subscribers apparatus
SAJ	Circuits of telephone subscribers apparatus
SAW	Circuits of telephone subscribers apparatus
SAX	Circuits of telephone subscribers apparatus
SC	Scales for electrical measuring instruments	Previously on CD
SD	Standard data
SHEET
SUB/A	Woolwich data drawings
SUB/B	Dover data drawings
SUB/C	Dalmuir data drawings
SUB/D	CS Ariel drawings
SUB/E	CS Iris drawings
SUB/F	CS Alert drawings
SUB/G	CS Sentinel drawings
SUB/H	Southampton CMD drawings
SUG/J	Misc Nautical drawings
SUB/K	Foreign charts
SUB/L	Contracts charts
SUB/LS	Misc equipment affecting all ships
SUB/M	Beacons at shore ends
SUB/N	Methil cable depot
SUB/P	CS Monarch drawings for cable ship equipt for PO use use designed externally
SUB/Q	CS Monarch drawings for cable ship equipt for PO use use designed externally
SUB/R	Cable section sheets
SUB/S	PO designed equipment
SUB/T	Cable shore ends
SUB/U	Common equipment for new ships
SUB/V
SUB/W	CS Iris
SUB/X	Greek consultancy
SUB/Z	Sketches, schedules, graphs etc
SUP/D	Packaging
T	Testing circuits and diagrams
TG	Telegraph ccts - theoretical
TG(L)	Telegraph ccts	loose leaf
TGM	Telegraph ccts
TGK	Telegraph ccts
TGU	Telegraph ccts
TGW	Telegraph ccts - wiring
TGX	Telegraph ccts
TK	Auto exchange trunking and grading diagrams
TL	Telephone, trunk, misc and power
TLU	Telephone, trunk, misc and power
TLW	Telephone, trunk, misc and power
TLX	Telephone, trunk, misc and power
TP	Telephone exchange equipment installation drawings and diagrams
TPW	Telephone exchange equipment installation drawings and diagrams
TPX	Cross connection field for meter pulse supplies
TRT	Testers for telephone exchange equipment
TRTM	Testers for telephone exchange equipment
TSB	Diagrams for test equipment
TSL	Diagrams for test equipment (test section Studd Street)
TSU	Drawings and diagrams for the Technical support unit
TTC	Training branch material
TU
WB	Laboratory drawings and diagrams
WB/WBM	Laboratory drawings and diagrams
WBM	Laboratory drawings and diagrams (assembly)
WBW	Laboratory drawings and diagrams
WE	War emergency diagrams (1939)
WL	Radio station drawings and maps
WM	Radio station drawings and maps
XED	Drawings and diagrams of non-standard equipment for experimental purposes
XM	ATE crossbar exchanges 5005
XP	ATE crossbar exchanges 5005
XQ	ATE crossbar exchanges 5005
XS	ATE crossbar exchanges 5005
XX	ATE crossbar exchanges 5005
Y	Diagrams and drawings for R12
Z	Drawings and diagrams for RS division before transfer to GCHQ

This list is included in the Diagram spreadsheet

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DIAGRAM INFORMATION

Last revised: November 03, 2025