AC Alternating current
ACD Automatic Call Distribution
AM (British) Air Ministry
AP Admiralty Pattern (precedes type number, on all manner of British Navy equipment)
APNSS Analogue Private Network Signalling System
ASTIC Anti-sidetone induction coil (circuit)
AUTO Automatic, fitted with a dial
AVO A particular UK make of multimeter (AVO stands for amps, volts, ohms) but often applied to any multimeter
ATE Automatic telephone exchange or the manufacturer AT&E Ltd
AWG American Wire Gauge. Almost the same as the British SWG
BABT British Approval Board for Telecommunications
BDF Building Distribution Frame
BSP Bell System Practice (US equivalent of an EI)
BT Block Terminal
BTR British Telecom Requirement
B/W Both way
CAI Common Air Interface
CAS Channel Associated Signalling
CB Central Battery (not fitted with a dial)
CBS Central battery signalling
CCITT Consultative Committee International Telegraph and Telephone
CCS Call Connect System
CNA Change of Number Announcement
CNI Change of Number Interception
COS Class of Service
CPE Customer premises equipment
CRA Call Routing Apparatus
CT Cordless telephone
CUG Closed User Group
Cx Continental (BPO expression)
DAS Directory Access System
DC Direct current.
DDD Direct Distance Dialling (the American expression for STD)
DDI Direct Dialling In
DECT Digital European Cordless Telephone
DEL Direct exchange line (i.e. not an extension or a private wire)
DES Direct Extension Select
DIS Disconnected, i.e. open circuit
DISA Direct Inward System Access
DND Do Not Disturb
DOVE Data Over Voice Equipment
DP Distribution Point
DPNSS Digital Private Network Signalling System
DS Dual signalling (loop-disconnect and DTMF)
DTE Data terminal Equipment
DTMF Dual tone multi frequency
AEROM Electrically alterable read only memory
EI Engineering Instruction (BPO, APO and NZPO expression)
ELR Earth Leg Recall
ETD Extension Trunk Dialling (direct extension-to-extension national dialling on British Railways)
ETSI European Telecommunications Standards Institute
FDDI Fibre Distributed Data Interface
FDM Frequency Division Multiplexing
FDP Floor Distribution Point
FNF Fault Not Found
IBTE Institution of British Telecommunications Engineers (former IPOEE).
IC Incoming or Integrated Circuit
ICD Internal Cable Distribution
IDA Integrated Digital Access
IDC Insulation Displacement Connection
IDD International Direct Dialling
IDN Integrated Digital Network
IEE Institute of Electrical Engineers
IEEE Institute of Electrical and Electronic Engineers (USA)
I/F Interface
IPOEE Institution of Post Office Electrical Engineers (now IBTE).
ISD International Subscriber Dialling, later retitled IDD
ISDN Integrated Services Digital Network
ISO International Standards Organisation
Ix International (BPO expression)
KS Kearny specification, named after the Western Electric plant in Kearny, New Jersey. KS numbers were applied to items made by Western Electric for the Bell System and to things made for Bell by other companies
KTS Key Telephone System
LAN Local Area Network
LCD Liquid Crystal Display
LCR Least Cost Routing
LED Light Emitting Diode
LD Loop Disconnect
LJU Line Jack Unit
LNR Last number redial.
LST Loudspeaking telephone.
MAT Maintenance Acceptance Test
MCL Mercury Communications Ltd
MD Manufacturer discontinued (Bell System expression, USA)
MDF Main Distribution Frame
MF Multi-frequency (often refers to signalling)
M, mic Microphone
MGS Miscellaneous government surplus
mil. spec. Military specification (high quality standard)
MMI Man, Machine interface
MOD Model, modification, modulation
MOH Music on Hold
MTBF Mean Time Between Failures
N Number
N/A Information not available
NCOP Network Code of Practice
NCP Network Connection Point
NDS Network Distribution System
NET Norme Europeenne de Telecommunications
NSN (on components) NATO stock number
NTP Network Terminating Point
NTTA Network Termination and Testing Apparatus
O/C Open circuit
PABX Private automatic branch exchange (with connection to the PSTN)
PAX Private automatic exchange (not connected to public networks)
PCB Printed circuit board or Poly Chlorinated Biphenol, a hazardous substance
PF               Picofarad
PH               Publicity handout (BPO expression)
PMG              Postmaster General (Australia)
PO Post Office
POEEJ Journal of the IPOEE
PPS Pulses per second
PS               Power supply
PST              Plug-and-socket terminated
PSTN Public switched telephone network
PSU              Power supply unit
PTO Public Telecoms Operator
PTT              Press-to-talk (method of switching from receive to  transmit) or Post, Telegraph and Telephone  administration
PU               Power unit or (gramophone) pick-up
PW Private Wire
PWB Printed wiring board (alternative expression for PCB)
pwr sup Power supply
PXML Private Exchange Master List
Q Abbreviation for capacitor or transistor on circuit diagram, alternatively the figure of merit for a tuned circuit
R, RCVR or RX Receiver
RAM Read access memory
ROM Read only memory
RWT Right When Tested
S/CRTNR or short Short circuit
SC Self-contained, i.e. a loop-disconnect push button telephone not requiring an external power supply
s.c.c. Silk-covered cotton (wire)
SCDC Single Commutation Direct Current
SCRA Small Call Routing Apparatus
SA Subscribers' Apparatus (also the prefix for a BPO series of drawings)
SPC Stored Programme Control
SR Special Range (prefix to BT title numbers)
STD Subscriber Trunk Dialling
STP Shielded Twisted Pair
SWG Standard Wire Gauge
T Telephone or tropicalised
TBR Time Break Recall
TDM Time Division Multiplex
TEMA Telecommunications Equipment Manufacturers Association
Tg Telegraph (BPO expression)
TI Technical Instruction (BPO expression)
TIA Telecommunications Industry Association
TJF Test Jack Frame
TMA Telephone Managers Association
TOS Temporary out of Service
Tp Telephone (BPO expression)
TR Transmit-receive
TUA Telecommunications Users Association
TX, TXMTR Transmitter (often used as a synonym for microphone)
TXD Telephone Exchange Digital
TXE Telephone Exchange Electronic
TXK Telephone Exchange Crossbar
TXS Telephone Exchange Strowger
UAX Unit automatic exchange
UPS Uninterrupted Power Supply
U/S Useless, unserviceable
UTP Unshielded Twisted Pair
VDU Visual Display Unit
VOM Volt-ohm meter, multimeter
VPN Virtual Private Network
VTVM Vacuum tube voltmeter, i.e. VVM
VVM Valve voltmeter, what people used before high-impedance multimeters became widely available
x General cypher used to shorten words
xcvr Receiver
xfmr Transformer
xistor,  xstr Transistor
xmit Transmit
xmtr Transmitter
xtal Crystal
WAN Wide Area Network


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Last revised: October 30, 2022