(IEC Class Codes) When would you use QA instead of FC?

[testsubject]

I do not see the need for QA instead of FC for Circuit Breakers. I think that they will always have protection as their primary function or we would just use a switch instead. Or am I missing something??

[dougmcalexander]

Q is used when the circuit breaker is used in power distribution.  For branch circuit protection you can and should use F.  The second letter is optional, according to IEC81346-2, but is included in AutoCAD Electrical's IEC60617 library anyway.

[testsubject]

Thanks Doug. That clears that up...

[dougmcalexander]

If you prefer the one-letter codes, use the IEC2 or IEC4 library.  You can employ a wd_fam.dat file to update the few symbols whose class designation letters changed since IEC61346-1. Here is a bit of an explanation of why this is needed.  IEC61346-1 was based upon the DIN standard.  Essentially, you could consider the IEC2 and IEC4 libraries as DIN libraries also.  It was a great system!  The one letter adequately conveyed function. 

I believe that the members of the International Electrotechnical Commission got bored, or felt that they must continue "tweaking" things in order to justify heir existence.  They approached the component class designations from a broader perspective and released IEC61346-2.  The letter "H", which had always represented a pilot light or indicator lamp, was changed to "P" for "Presenting Information".  The letter "H" was no longer assigned in IEC61346-2, but was marked for future use.  The letter "L" for inductor is now "R" for resistance.  The letter "D" for diode is now "R" for resistance.  Resistors are still "R" as well.  Again, the class designations are based on a more broad sense of function, rather than actual electrical function. 

I prefer to use a wd_fam.dat file in conjunction with library IEC4, rather than use the two-letter designations from the IEC60617 library.  My file takes all symbols with the letter "H" as their class designation and changes them to "P", letter "L" changes to "R", etc.  Listed below are the entries in the wd_fam.dat file I use for the IEC course I teach for AutoCAD Electrical.

H,P

L,R

D,R

Y,Q

GND,PE

IEC81346-2 added a purpose for the letter "H", which is, "Producing a new kind of material or product".  Do you see what I mean about the new designations being broad?  IEC81346-2 also introduced a table with the optional two-letter codes, so the new class designations can make as much sense as IEC61346-1 did.  It is funny to me.  I don't really care for IEC81346-2 at all.  I still prefer the DIN standard or IEC61346-1, where one letter was enough.