Is there a list of standard ID codes used for components on a schematic drawing that anyone can point to?


K = Contactor
S = Switch
Y = Solenoid
X = Terminal strip


Any list would be good, although if there is anything relating to Australian Standards that would be great.


2 Answers 2


These are from AS 3702, Item Designation in Electrotechnology. This is equivalent to IEC 60750.

There is a three-page long table of "Item" vs. "Letter Code" including -

Contactor                        K
Relay                            K
Switching devices for control    S
Switching devices for power      Q
Solenoid                         Y
Terminal                         X

For countries following American practice, the Reference Designators come from IEEE 315-1975 and IEEE 200-1795. These are different to the AS / IEC letter codes.

  • \$\begingroup\$ Why is everything crossed out ? \$\endgroup\$
    – efox29
    Commented Nov 12, 2015 at 11:16
  • \$\begingroup\$ @efox29 Because I made two attempts at answering the question. The first attempt was wrong (for Australian context.) \$\endgroup\$ Commented Nov 12, 2015 at 11:40
  • \$\begingroup\$ Then perhaps remove (not cross out) anything that is no relevant to the question. I see that @passerby linked to a question which has similar content to the crossed out content of this answer. \$\endgroup\$
    – efox29
    Commented Nov 12, 2015 at 11:42
  • \$\begingroup\$ @efox29: I just edited. \$\endgroup\$ Commented Nov 12, 2015 at 11:43
  • 1
    \$\begingroup\$ @Andy: Yes, it appears to have been superceded as of... about two weeks ago. I haven't read IEC 81346 yet. \$\endgroup\$ Commented Nov 13, 2015 at 3:15

Although a year later, I stumbled across this and then found some guidelines which I am adapting to my needs, so thought I might share my findings.

The ISO/IEC 81346 one letter codes are available online. There is also a introductory video explaining the Reference Designator System they work on for the "common language" attempt for systems. Here is a compiled/merged list of the one Letter codes from their current edition 2016 and 2017 draft.

  • A: (multi_function) Two or more purposes or tasks
  • B: (sense) picking up information and providing a representation
  • C: (store) storing for subsequent retrieval
  • E: (emit) emitting
  • F: (protect) protecting against the effects of dangerous or undesirable conditions
  • G: (generate) providing a controllable flow
  • H: (process matter) treating matter
  • K: (process information) treating input signals and providing an appropriate output
  • M: (drive) providing mechanical movement or force
  • N: (cover) enclosing partly or fully another object
  • P: (present) providing perceptible information
  • Q: (control) controlling access or flow
  • R: (restrict) restricting or stabilising
  • S: (interact) detecting a manual action and providing an appropriate response
  • T: (transform) transforming
  • U: (hold) structural positioning of other objects
  • W: (guide) leading from one place to another
  • X: (interface) interfacing an object

Taking as reference examples Li-aung Yips' answer, I would interpret to use the following codes.

  • Contactor : Q
  • Relay : K
  • Switching devices for control
    • Automatic : K
    • Manual : S
  • Switching devices for power : Q
  • Solenoid : QM ?
  • Terminal : X
  • \$\begingroup\$ I am also unsure of the designator for a solenoid coil, based on the new 81346-2 2017 standard. What would a 1 letter code be? "Y" doesn't seem to be a defined class so should it be "M"? Also, how would you reference a PLC with a one letter code? \$\endgroup\$
    – Andy
    Commented Dec 12, 2016 at 22:18
  • 1
    \$\begingroup\$ @Andy For the Solenoid case it would depend on its specific purpose/functionality within the design. Without knowing that and needing to be limited to one letter I would use M as you are providing a mechanical force. For the PLC (Programmable Logic Controller), depending on the complexity of the task the PLC is doing, I would use either K (less complex) or A (more complex). \$\endgroup\$ Commented Dec 13, 2016 at 16:37
  • \$\begingroup\$ 'A' makes sense, but it doesn't seem to be defined as a class in the 81356-2 2017 edition as far as I can tell 81346.com/english/about-81346/about-81346-2-2016-edition \$\endgroup\$
    – Andy
    Commented Dec 13, 2016 at 21:40
  • \$\begingroup\$ Although an old post, from 2009, it is an interesting one where the composition of letters in reference deisgnators for Function, Product, Location of objects is explained and several standards are referenced. \$\endgroup\$ Commented Dec 14, 2016 at 15:34

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