Short Answer
The prefixes ‘K’ and ‘Q’ are from standards about ‘item designation’. Countries using European standards started out using IEC 60750, Item designation in electrotechnology. Countries using American standards use IEEE Std 315-1975 / ANSI Y32.2, Graphic symbols for electrical and electronic diagrams. Relays are called ‘K’ because IEC 60750 and IEEE 3
Longer Answer
There are standardised “Letter codes for the designation of kind of item”. In Australia, we use letter codes based on AS 3702, “Item designation in electrotechnology”. AS 3702 is essentially IEC 60750 with some extra information in the appendices.
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Historical Notes
The original IEC standard was IEC 60113:1959, which was superseded by IEC 60750:1983. AS 3702:1989 derives from IEC 60750. IEC 60750 was superceded by the IEC 61346 series (1996), which was superceded by the IEC 81346 series (2009) in turn. IEC 81346 is about 300 pages - much larger than AS 3702, which is only 24 pages If you are only interested i
References
AS 3702-1989 - “Item designation in electrotechnology”. Equivalent to IEC 60750 Ed 1.0 (1983).AS 1103.2-1982 - “Diagrams charts and tables for electrotechnology, Part 2: Item Designation” (Superseded by AS 3702-1989.)IEC 750-1983 - AS 3702 is equivalent, but provides extra information.IEC 113 (superseded by IEC 750, i.e. IEC 60750.)
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