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{{Short description|Location identifier for a circuit component}}
A '''reference designator''' unambiguously identifies the location of a [[Electronic component|component]] within an [[circuit diagram|electrical schematic]] or on a [[printed circuit board]]. The reference designator usually consists of one or two letters followed by a number, e.g. C3, D1, R4, U15. The number is sometimes followed by a letter, indicating that components are grouped or matched with each other, e.g. R17A, R17B.  The [[IEEE]] 315 standard 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.

== History ==
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.

== Definition ==
ASME Y14.44-2008<ref name="ASME-Y14.44-2008">{{cite book | title = Reference Designations for Electrical and Electronics Parts and Equipment: ASME Y14.44-2008 (Replaced IEEE 200-1975) | publisher = ASME, Fairfield, NJ | year = 2008 | url = https://www.asme.org/products/codes-standards/reference-designations-for-electrical-and-electron}}</ref> and IEEE 315-1975<ref name="IEEE-315-1975">{{Citation | last = IEEE | date = 1975 | title = IEEE Std 315-1975: Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters) (Reaffirmed 1993) | chapter = 22. Class Designation Letters | publisher = IEEE and ANSI, New York, NY }}</ref> 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<ref name="IEEE-315-1975" /> defines separate class designation letters for ''separable'' assemblies (class designation 'A') and ''inseparable'' assemblies (class designation 'U'). Inseparable assemblies&mdash;i.e., "items which are ordinarily replaced as a single item of supply"<ref name="IEEE-315-1975" />&mdash;are typically treated as components in this referencing scheme.

Examples:
* 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:
* 1A1W35P1
* 1A1W35P2

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

The construction of reference designators is covered by IEEE 200-1975/ANSI Y32.16-1975<ref>{{cite book | title = Standard Reference Designations for Electrical and Electronics Parts and Equipments: IEEE 200-1975 (Reaffirmed 1988): Section 4.1.5.3 (2) | publisher = IEEE and ANSI, New York, NY | year = 1975 }}</ref> (replaced by ASME Y14.44-2008<ref name="ASME-Y14.44-2008" />) and IEEE-315-1975.<ref name="IEEE-315-1975" />

==Designators==
The table below lists designators commonly used, and does not necessarily comply with standards.  For modern use, designators are often simplified towards shorter designators, because it requires less space on silkscreens.

{| class="wikitable"
|-
! Designator
! Component type
! Modern use
|-
| A || Separable assembly or sub-assembly (e.g. [[printed circuit assembly]]) ||
|-
| AT || [[Attenuator (electronics)|Attenuator]] or [[isolator switch|isolator]] ||
|-
| BR || [[Bridge rectifier]] (four diodes in a package) || often changed to "D" for diode
|-
| BT || [[Battery (electricity)|Battery]] || often shortened to "B"
|-
| C || [[Capacitor]] ||
|-
| CN || [[Capacitor#Circuit analysis|Capacitor network]] || may be simplified to "C" for capacitor
|-
| D, CR || [[Diode]] (all types, including [[light-emitting diode|LED]]), [[thyristor]] || "D" is preferred for various types of diodes
|-
| DL || [[Delay-line memory|Delay line]] ||
|-
| DS || [[Display device|Display]], general light source, lamp, signal light ||
|-
| F || [[Fuse (electrical)|Fuse]] ||
|-
| FB || [[Ferrite bead]] || sometimes changed to "L" for inductor, though "E" was used in the currently inactive standard IEEE 315 (see Clause 22.4).
|-
| FD || [[Fiduciary marker|Fiducial]] ||
|-
| FL || [[Filter (signal processing)|Filter]] ||
|-
| G || [[Electric generator|Generator]] or [[oscillator]] ||
|-
| GL || Graphical logo ||
|-
| GN || General network ||
|-
| H || [[Household hardware|Hardware]], e.g., screws, nuts, washers || sometimes hardware is expanded to "HW"
|-
| HY || [[Circulator]] or [[directional coupler]] ||
|-
| IR || Infrared diode || often changed to "D" for diode
|-
| J || [[Electrical connector|Jack]] (least-movable connector of a connector pair), [[jack connector]] (connector may have "male" pin contacts and/or "female" socket contacts) || all types of [[electrical connector|connectors]], including [[pin header]]s.
|-
| JP || [[Jumper (computing)|Jumper (link)]] ||
|-
| K || [[Relay]] or [[contactor]] ||
|-
| L || [[Inductor]] or coil or [[ferrite bead]] ||
|-
| LS || [[Loudspeaker]] or [[buzzer]] ||
|-
| M || [[Electric motor|Motor]] ||
|-
| MK || [[Microphone]] ||
|-
| MP || Mechanical part (including screws and fasteners) ||
|-
| OP || [[Opto-isolator]] ||  often changed to "U" for IC
|-
| P || [[Plug (connector)|Plug]] (most-movable connector of a connector pair), plug connector (connector may have "male" pin contacts and/or "female" socket contacts) ||
|-
| PS || [[Power supply]] ||
|-
| Q || [[Transistor]] (all types) ||
|-
| R || [[Resistor]] ||
|-
| RN || [[Resistor#Series and parallel resistors|Resistor network]] || sometimes simplified to "R" for resistor, or "N" for network
|-
| RT || [[Thermistor]] || sometimes simplified to "R" for resistor
|-
| RV || [[Varistor]], variable resistor ||
|-
| S, SW || [[Switch]] (all types, including buttons) ||
|-
| SA || [[Spark gap|Spark Arrester]] ||
|-
| T || [[Transformer]] || sometimes changed to "L" for inductor
|-
| TC || [[Thermocouple]] ||
|-
| TP || [[Test point]] ||
|-
| TUN || [[Tuner (electronics)|Tuner]] ||
|-
| U, IC || [[Integrated circuit]] (IC) || shorter "U" (unit) is preferred instead of "IC"
|-
| V || [[Vacuum tube]] ||
|-
| VR || [[Voltage regulator]] (voltage reference), or [[variable resistor]] (potentiometer / trimmer / rheostat) || voltage regulators are often "U" for IC, pots and trimmers often "R" for resistor
|-
| X || Socket 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.) ||
|-
| X, XTAL, Y || [[Crystal oscillator|Crystal]], [[Ceramic resonator|ceramic resonator]], [[Electronic oscillator|powered oscillator]] ||
|}

==Other designators==
{{columns-list|colwidth=20em|
* AE: [[Antenna (radio)|Aerial, antenna]]
* ASSY: Separable assembly
* B: [[Battery (electricity)|Battery]]
* CN: [[Electrical connector|Connector]]
* CRT: [[Cathode ray tube]]
* DSP: [[Digital signal processor]]
* FET: [[Field-effect transistor]]
* GDT, SVP: [[Surge protector#Gas discharge tube (GDT) spark gap|Gas discharge tube, surge voltage protector]]
* H: [[Pin header]]
* J, JW: [[Jumper (computing)|Wire link ("jumper")]]
* JFET: [[JFET|Junction gate field-effect transistor]]
* LA: [[Lightning arrester]]
* LCD: [[Liquid crystal display]]
* LDR: [[Photoresistor|Light-dependent resistor]]
* LED: [[Light-emitting diode]]
* MCB: Miniature [[circuit breaker]]
* MIC: [[Microphone]]
* MOSFET: [[MOSFET|Metal-oxide-semiconductor field-effect transistor]]
* MOV: [[Metal-oxide varistor]]
* NE: [[Neon lamp]]
* PCB: [[Printed circuit board]]
* PLC: [[Programmable logic controller]]
* PU: [[Pickup tube|Pickup]]
* RY, RLA: [[Relay]]
* SCR: [[Silicon-controlled rectifier]]
* SUS: Silicon unilateral switch
* SW: [[Switch]]
* TFT: [[TFT LCD|Thin-film transistor (display)]]
* TH: [[Thermistor]]
* VC: [[Variable capacitor]]
* VDR: [[Voltage-dependent resistor]]
* VFD: [[Vacuum fluorescent display]]
* VT: Voltage transformer
* W: [[Wire]]
}}<!-- end of columns-list -->

==See also==
{{Portal|Electronics}}
* [[Circuit diagram]]
* [[Electronic symbol]]

==References==
{{Reflist|30em}}

[[Category:Electronic engineering]]