Fuse Reference Designator Assignment

A            Assembly

AR         Amplifier

AT         Attenuator; Isolator

B            Blower

BR         Bridge Rectifier

BT         Battery

C            Capacitor

CB         Circuit Breaker

CN         Capacitor Network

CP         Coupler

CR         Diode or Silicon Rectifier

D            Diode; Thyristor; Varacter

DC         Directional Coupler

DP         Duplexer

DL         Delay Line

DS         Digital Display; LED Lamp

E            Miscellaneous Electrical Part

F            Fuse

FB          Ferrite

FD         Fiducial

FL          Filter

G           Generator

HW        Hardware

HY         Circulator

I or ICT In Circuit Test Point

J            Jack Connector

JP          Configuration Jumper

K           Relay

L            Coil; Inductor

LS          Loud Speaker/Buzzer

M           Motor

MG        Motor-Generator

MH        Mounting Hole

MK        Microphone

MP         Mechanical Part

P            Plug Type Connector

PS          Power Supply

Q           Transistor

R            Resistor

RN         Resistor Network

RT         Thermistor

S            Switch

T            Transformer

TB         Terminal Block

TC         Thermocouple

TP          Test Point

U            Tuner

U            Integrated Circuit

V            Electron Tube

VR         Voltage Regulator

W           Cable Transmission

X            Sub-circuit

Y            Crystal or Oscillator

Z            Ref Des Suppressed

A reference designator unambiguously identifies a component in an electrical schematic or on a printed circuit board. The reference designator usually consists of one or two letters followed by a number, e.g. R13, C1002. The number is sometimes followed by a letter, indicating that components are grouped or matched with each other, e.g. R17A, R17B. IEEE 315 contains a list of Class Designation Letters to use for electrical and electronic assemblies. For example, the letter R is a reference prefix for the resistors of an assembly, C for capacitors, K for relays.


IEEE 200-1975 or "Standard Reference Designations for Electrical and Electronics Parts and Equipments" is a standard that was used to define referencing naming systems for collections of electronic equipment. IEEE 200 was ratified in 1975. The IEEE renewed the standard in the 1990s, but withdrew it from active support shortly thereafter. This document also has an ANSI document number, ANSI Y32.16-1975.

This standard codified information from, among other sources, a United States military standard MIL-STD-16 which dates back to at least the 1950s in American industry.

To replace IEEE 200-1975, ASME, a standards body for mechanical engineers, initiated the new standard ASME Y14.44-2008. This standard, along with IEEE 315-1975, provide the electrical designer with guidance on how to properly reference and annotate everything from a single circuit board to a collection of complete enclosures.


ASME Y14.44-2008[1] and IEEE 315-1975[2] define how to reference and annotate components of electronic devices.

It breaks down a system into units, and then any number of sub-assemblies. The unit is the highest level of demarcation in a system and is always a numeral. Subsequent demarcation are called assemblies and always have the Class Letter "A" as a prefix following by a sequential number starting with 1. Any number of sub-assemblies may be defined until finally reaching the component. Note that IEEE-315-1975[2] defines separate class designation letters for separable assemblies (class designation 'A') and inseparable assemblies (class designation 'U'). Inseparable assemblies—i.e., "items which are ordinarily replaced as a single item of supply"[2]—are typically treated as components in this referencing scheme.


  • 1A12A2R3 - Unit 1, Assembly 12, Sub-assembly 2, Resistor 3
  • 1A12A2U3 - Unit 1, Assembly 12, Sub-assembly 2, Inseparable Assembly 3

Especially valuable is the method of referencing and annotating cables plus their connectors within and outside assemblies. Examples:

  • 1A1A44J5 - Unit 1, Assembly 1, Sub-Assembly 44, Jack 5 (J5 is a connector on a box referenced as A44)
  • 1A1A45J333 - Unit 1, Assembly 1, Sub-Assembly 45, Jack 333 (J333 is a connector on a box referenced as A45)

A cable connecting these two might be:

  • 1A1W35 - In the assembly A1 is a cable called W35.

Connectors on this cable would be designated:

ASME Y14.44-2008 continues the convention of Plug P and Jack J when assigning references for electrical connectors in assemblies where a J (or jack) is the more fixed and P (or plug) is the less fixed of a connector pair, without regard to the gender of the connector contacts.

The construction of reference designators is covered by IEEE 200-1975/ANSI Y32.16-1975[3] (replaced by ASME Y14.44-2008[1]) and IEEE-315-1975.[2] The table below lists designators commonly used, and does not necessarily comply with the standard.

DesignatorComponent Type
ASeparable assembly or sub-assembly (e.g. printed circuit assembly)
ATAttenuator or isolator
BRBridge rectifier
CNCapacitor network
DDiode (including LED, TVS, Thyristor, Zener)
DLDelay line
FBFerrite bead
GGenerator or oscillator
GNGeneral Network
HHardware, e.g., screws, nuts, washers
HYCirculator or directional coupler
JJack (least-movable connector of a connector pair) | Jack connector (connector may have "male" pin contacts and/or "female" socket contacts)
JPJumper (Link)
KRelay or contactor
LInductor or coil or ferrite bead
LSLoudspeaker or buzzer
MPMechanical part (including screws and fasteners)
PPlug (most-movable connector of a connector pair) | Plug connector (connector may have "male" pin contacts and/or "female" socket contacts)
PSPower supply
QTransistor (all types)
RNResistor network
SSwitch (all types, including push-buttons)
TPTest point
UIntegrated Circuit (IC)
VVacuum tube
VRVariable resistor (potentiometer or rheostat)
XSocket connector for another item not P or J, paired with the letter symbol for that item (XV for vacuum tube socket, XF for fuse holder, XA for printed circuit assembly connector, XU for integrated circuit connector, XDS for light socket, etc.)
YCrystal or oscillator
ZZener diode

Other component name abbreviations used in industry[edit]

See also[edit]


  1. ^ abReference Designations for Electrical and Electronics Parts and Equipment: ASME Y14.44-2008 (Replaced IEEE 200-1975). ASME, Fairfield, NJ. 2008. 
  2. ^ abcdIEEE (1975), "22. Class Designation Letters", IEEE Std 315-1975: Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters) (Reaffirmed 1993), IEEE and ANSI, New York, NY 
  3. ^Standard Reference Designations for Electrical and Electronics Parts and Equipments: IEEE 200-1975 (Reaffirmed 1988): Section (2). IEEE and ANSI, New York, NY. 1975. 


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