Appendix B: Class Designation Letters

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  1. Reference Designations For Electrical And Electronics Parts And Equipment (this document)
  2. Appendix A: List of Pertinent Applicable Standards
  3. Appendix B: Class Designation Letters
  4. Appendix C: List of Nonconforming Class Letters
  5. Appendix D: System Subdivision (diagram)
  6. Appendix E: KiCad Anomalous Handling of Suffix Letters
  7. Appendix F: Scenario Questions and Answers

APPENDIX B. Class Designation Letters

Clause 0. Class Designation Letters

For use in assignment of reference designations for electrical and electronics parts and equipment as described in ANSI/ASME Y14.44, Reference Designations for Electrical and Electronics Parts and Equipment.

Clause 0.1Class Designation Letter

The letters identifying the class of an item shall be selected in accordance with the list in clause 0.4.

Certain item names and designating letters may apply to either a part or an assembly.

Clause 0.2Special Considerations for Class Designation Letter Assignment

Clause 0.2.1Actual versus intended function

If a part serves a purpose other than its generally intended one, the function actually performed shall be represented by the graphic symbol used on the schematic diagram; the class letter shall be chosen from the list in clause 0.4 and shall be indicative of its physical characteristics. For example, a semiconductor diode used as a fuse would be represented by the graphic symbol for a fuse (actual function), but the class letter would be D (class of part). If a part has a dual function, the class letter for the principal physical characteristic of the part shall apply.

Clause 0.2.2Assembly versus subassembly

The term subassembly as used herein shall apply equally to an assembly.

Clause 0.2.3Subassembly versus individual part

A group of parts shall not be treated as a subassembly unless it is one or more of the following:

a) A plug-in item.

b) A significant item covered by a separate schematic.

c) A multiapplication item.

d) Likely to be handled as a replaceable item for maintenance purposes.

Clause 0.2.4Specific versus general

The letters A and U (for assembly) shall not be used if more specific class letters are listed in clause 0.4 for a particular item.

Clause 0.2.5Inseparable subassemblies

Potted, embedded, riveted, or hermetically sealed subassemblies, modular assemblies, printed circuit boards, and IC packages and similar items which are ordinarily replaced as a single item of supply shall be treated as parts. They shall be assigned the class letter U, unless a more specific class letter is applicable.

Clause 0.4 Class Designation Letters: Alphabetical List

Parts not specifically included in this list shall be assigned a letter or letters from the list below for the part or class most similar in function.

 

A (see also U and 0.2.4)[1]electronic divider
electronic function generator (other than rotating)
electronic multiplier
facsimile set
field-polarization amplitude modulator
field-polarization rotator
general circuit element
gyroscope
integrator
positional servomechanism
sensor (transducer to electric power)
separable assembly[2]
separable subassembly
telephone set
telephone station
teleprinter
teletypewriter
ARamplifier (other than rotating)
repeater
ATbolometer
capacitive termination
fixed attenuator
inductive termination
isolator (nonreciprocal device)
pad
resistive termination
Bblower
motor
synchro
BTbarrier photocell
battery
battery cell
blocking layer cell
photovoltaic transducer
solar cell
Ccapacitor bushing
capacitor
CBcircuit breaker
network protector
CPconnector adapter
coupling (aperture, loop, or probe)
junction (coaxial or waveguide)
D or CRasymmetrical varistor
crystal diode
current regulator (semiconductor device)
diode type ring demodulator
diode rectifier (semiconductor type)
diode-type ring demodulator
diode-type ring modulator
metallic rectifier
photodiode (photosensitive type)
stabistor
thyristor (semiconductor diode type)
varactor
D or VRbreakdown diode (voltage regulator)
overvoltage absorber
DCdirectional coupler
DLdelay function
delay line
slow-wave structure
DSalphanumeric display device
annunciator
electrically restored drop
general light source
indicator (excluding meter or thermometer)
lamp (excluding heating lamp)
light-emitting solid-state device
manually restored drop
photodiode (photoemissive type)
signal light
visual alarm
visual indicator
visual signaling device
Ealuminum cell
antenna
armature
binding post
cable termination
carbon block
circuit terminal
conductivity cell
electrical contact
electrical contact brush
electrical shield
electrolytic cell
ferrite bead rings [toroid]
film element
gap (horn, protective, or sphere)
Hall element
ignitor gap
insulator
lightning arrester
magnetic core
miscellaneous electrical part
optical shield
permanent magnet
rotary joint (microwave)
short circuit (termination)
spark gap
splice
telephone protector
telephone protector block
terminal (individual)
valve element
vibrating reed
EQequalizer
equalizing network
Fcurrent limiter (for power cable)
fuse
fuse cutout
FD[6]fiducial. An SMT optical target for automatic placement of part
Gelectronic chopper
generator
ignition magneto
interrupter vibrator
oscillator
rotating amplifier (regulating generator)
telephone magneto
Hhardware (common fasteners, etc)
HPhydraulic part
HRheater
heating lamp
heating resistor
infrared lamp
thermomechanical transducer
HShandset
operator’s set
HTearphone
electrical headset
receiver (excluding radio receiver)
telephone receiver
HYcirculator
directionally selective transmission device
hybrid circuit network
hybrid coil (telephone usage)
hybrid junction (magic T)
Jdisconnecting device (receptacle connector)
electrical receptacle connector
jack
receptacle (connector, stationary portion)
waveguide flange (choke)
Kcontactor (magnetically operated)
relay
Lcoil (all not classified as transformers)
electrical solenoid
field winding
generator field
inductor
lamp ballast
motor field
reactor
winding
LSaudible alarm
audible signaling device
buzzer
electric bell
electric horn
loudspeaker
loudspeaker-microphone
siren
telephone ringer
telephone sounder
underwater sound transducer
Mclock
coulomb accumulator
elapsed time recorder
electric timer
electrical counter
electrochemical step-function device
instrument
message register
meter
meter-type level pressure gage
oscillograph
oscilloscope
position indicator
thermometer
MGconverter (rotating machine)
dynamotor
inverter (motor-generator)
motor-generator
MKhydrophone
microphone
telephone transmitter
MPbrake
clutch
mechanical interlock
mechanical part
miscellaneous mechanical part (bearing, coupling, gear, shaft)
MSC[6]miscellaneous [tape, chemicals, RTV, labels, etc.]
MTaccelerometer
measuring transducer
mode transducer
motional pickup transducer
primary detector
N[3]equipment subdivision
NPH[6]non-plated through hole
Pdisconnecting device (plug connector)
electrical plug connector
plug (connector, movable portion)
waveguide flange (plain)
PSpower supply
rectifier (complete power-supply assembly)
PTH[6]plated through hole
PUhead (with various modifiers)
sound reproducer
Qsemiconductor controlled rectifier
semiconductor controlled switch
phototransistor (3 terminal)
thyratron (semiconductor device)
thyratron (semiconductor triode type)
transistor
Rfunction potentiometer
instrument shunt
magnetoresistor
potentiometer
relay shunt
resistor
rheostat
REradio receiver
REF[6]reference [usually to a document or DWG]
RTballast lamp
ballast tube
current-regulating resistor
resistance lamp
temperature-sensing element
thermal resistor
thermistor
RVsymmetrical varistor
voltage-sensitive resistor
Scontactor (manually, mechanically, or thermally operated)
disconnecting device (switch)
electrical safety interlock
flasher (circuit interrupter)
governor (electrical contact type)
speed regulator (electrical contact type)
switch
telegraph key
telephone dial
thermal cutout (circuit interrupter—not visual)
thermostat
SJ[6]solder jumper pads [SMT]
SP[6]software program
software set
SQelectric squib
explosive squib
fusible link
igniter squib
sensing link
SRelectrical contact ring
rotating contact
slip ring
Tautotransformer
coaxial taper
linear coupler
telephone induction coil
telephone repeating coil
transformer
waveguide taper
TBconnecting strip
terminal board
terminal strip
test block
TCsemiconductor thermocouple
thermocouple
thermopile
TP[4]test point
TRradio transmitter
U (see also A and 0.2.4)[1]inseparable assembly
integrated-circuit package
microcircuit
micromodule
photon-coupled isolator
Velectron tube
Geiger-Muller counter tube
ionization chamber
klystron
magnetron
phototube
proportional counter tube
resonator tube (cavity type)
solion
thyratron (electron tube)
traveling-wave tube
voltage regulator (electron tube)
VR (see also D)induction voltage regulator
voltage regulator (excluding electron tube)
Wbus bar
cable
cable assembly (with connectors)
coaxial cable
conductor
distribution line
distribution path
Goubau line
strip-type transmission line
transmission line
transmission path
waveguide
wire
WT[5]wiring tiepoint
Xfuseholder
lampholder
socket
Ymagnetostriction oscillator
piezoelectric crystal unit
quartz crystal unit
tuning-fork resonator
Zartificial line (other than delay line)
balun
carrier-line trap
coupled tunable resonator
directional phase shifter (non-reciprocal)
discontinuity (usually coaxial or waveguide transmission use)
E-H tuner
general network (where specific class letters do not fit)
gyrator
mode suppressor
multistub tuner
phase shifter
phase-changing network
resonator (tuned cavity)
slide-screw tuner

[1] The class letter A is assigned on the basis that the item is separable. The class letter U shall be used if the item is inseparable.

[2] For economic reasons, assemblies which are fundamentally separable may not be so provisioned but may be supplied as complete assemblies. However, the class letter A shall be retained.

[3] Not a class letter, but used to identify a subdivision of an equipment in the Location Numbering Method.

[4] Not a class letter, but commonly used to designate test points for maintenance purposes.

[5] Not a class letter, but commonly used to designate a tiepoint on connection diagrams.

[6] This class letter is added.