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What prefixes should be used on reference designators for components of various types? I think we can all agree that "R##" refers to a resistor, "C##" refers to a capacitor, and "L##" refers to an inductor. Beyond that, it appears to be a mishmash of conventions.

I've seen both "IC" and "U" used for chips. "Q", "T", and "M" have been used for transistors and MOSFETs. Ordinarily, "D##" is used for diodes, but LEDs and Zeners get special treatment on some boards.

What standards are available for reference, and who endorses them? JEDEC, ISO, IEEE, and other standardization bodies are welcome references (though I'd prefer an inexpensive standard), but I'm also curious to see what's used at various companies other than my own.

Edit: What I'd really like to see is a list in an answer here which complies with the standard (even if it's just a quote).

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  • \$\begingroup\$ The nice thing about standards is that there are so many to choose from. (In other words, look at a variety of schematics, and choose something that makes sense to you.) \$\endgroup\$ – Peter Bennett Jul 25 '18 at 3:35
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There are actually standards to address this, IEC 60617 (also known as British Standard BS 3939), ANSI standard Y32 (also known as IEEE Std 315), Australian Standard AS 1102

Below is a table of some common markings from this link to an old revision of a Wikipedia article

  • Designator Component Type
  • AT Attenuator
  • BR Bridge rectifier
  • BT Battery
  • C Capacitor
  • CN Capacitor network
  • D Diode (including zeners, thyristors and LEDs)
  • DL Delay line
  • DS Display
  • F Fuse
  • FB or FEB Ferrite bead
  • FD Fiducial
  • J Jack connector (female)
  • JP Link (Jumper)
  • K Relay
  • L Inductor
  • LS Loudspeaker or buzzer
  • M Motor
  • MK Microphone
  • MP Mechanical part (including screws and fasteners)
  • P Plug connector (male)
  • PS Power supply
  • Q Transistor (all types)
  • R Resistor
  • RN Resistor network
  • RT Thermistor
  • RV Varistor
  • S Switch (all types, including push-buttons)
  • T Transformer
  • TC Thermocouple
  • TUN Tuner
  • TP Test point
  • U Integrated circuit
  • V Vacuum Tube
  • VR Variable Resistor (potentiometer or rheostat)
  • X Transducer not matching any other category
  • Y Crystal or oscillator
  • Z Zener Diode


Component name abbreviations widely used in industry:

  • AE: aerial, antenna
  • B: battery
  • BR: bridge rectifier
  • C: capacitor
  • CRT:cathode ray tube
  • D or CR: diode
  • DSP:digital signal processor
  • F: fuse
  • FET:field effect transistor
  • GDT: gas discharge tube
  • IC: integrated circuit
  • J: wire link ("jumper")
  • JFET: junction gate field-effect transistor
  • L: inductor
  • LCD:Liquid crystal display
  • LDR: light dependent resistor
  • LED: light emitting diode
  • LS: speaker
  • M: motor
  • MCB: circuit breaker
  • Mic: microphone
  • MOSFET:Metal oxide semiconductor field effect transistor
  • Ne: neon lamp
  • OP: Operational Amplifier
  • PCB: printed circuit board
  • PU: pickup
  • Q: transistor
  • R: resistor
  • RLA: RY: relay
  • SCR: silicon controlled rectifier
  • SW: switch
  • T: transformer
  • TFT:thin film transistor(display)
  • TH: thermistor
  • TP: test point
  • Tr: transistor
  • U: integrated circuit
  • V: valve (tube)
  • VC: variable capacitor
  • VFD: vacuum fluorescent display
  • VLSI:very large scale integration
  • VR: variable resistor
  • X: crystal, ceramic resonator
  • XMER: transformer
  • XTAL: crystal
  • Z or ZD: Zener diode
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  • \$\begingroup\$ The Wikipedia article has both a table and a list. The table says "The table below lists designators commonly used, and does not comply with the standard." The list says "Component name abbreviations widely used in industry." But, upvoted for the list standards and the Wikipedia references to those standards (and others). \$\endgroup\$ – Kevin Vermeer Feb 17 '11 at 19:31
  • \$\begingroup\$ Quick note: AS 1102 / IEC 60617 are for graphical symbols. Letter designators are from AS 3702 / IEC 60750. See electronics.stackexchange.com/questions/200428/…. \$\endgroup\$ – Li-aung Yip Nov 12 '15 at 11:45
  • \$\begingroup\$ Quick note: IEC60750 is redrawn and the newer ISO/IEC 81346:2009 includes reference designators \$\endgroup\$ – oldtimer Jun 6 at 6:13
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I've used the canonical R, C, D, Q, U scheme at both career stops thus far.

My first stop would differentiate between 'male' and 'female' connectors by using J for 'jacks' (i.e. female) and P for 'pins' (i.e. male).

I currently use RT for NTC/PTC thermistors and RV for MOVs. Odd that the powers-that-be only opted for such a narrow amount of reference designator innovation.

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  • \$\begingroup\$ What makes that scheme canonical? \$\endgroup\$ – Kevin Vermeer Feb 17 '11 at 5:02
  • \$\begingroup\$ Sounds about the same as what I've seen. \$\endgroup\$ – Nick T Feb 17 '11 at 5:02
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    \$\begingroup\$ I suppose since the overwhelming majority of books, schematics, etc. that I've seen use this scheme. \$\endgroup\$ – Adam Lawrence Feb 17 '11 at 17:30
  • \$\begingroup\$ Wow, a downvote 3 years later... \$\endgroup\$ – Adam Lawrence Mar 29 '14 at 2:42
  • \$\begingroup\$ Probably for describing something without a prescribed standard as "canonical". \$\endgroup\$ – Marshall Eubanks Mar 5 '18 at 18:52
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The standard list of class designation letters is contained in IEEE 315, Clause 22.4. P is not a male connector, it is the most movable of a pair. And J is not a female connector, it is the most fixed of a pair. A connecting pair of sexless connectors, such as an APC-7, would follow this convention.

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