I suspect that we can blame Ma Bell for this practice of using NEMA 2-20 connectors for 12vdc.. That is the connector commonly used on service trucks for manhole blowers, drop lights, and similar. I suspect the practice dates back many years, probably long before the NEMA standard was introduced.

for the 120/208 60hz vs 400hz example, I will note that there are actually specific connectors for 400hz use.

All of these are 30A twistlock type.
FSL2 - 30A 120V 400HZ (similar to L5-30)
FSL3 - 30A 120V 3phase delta 400HZ (similar to L15-30) (yes, I know the voltage should probably be 250v, but that is how it is listed in my 1994 Bryant catalog)
FSL4 - 30A 120/208Y 400HZ (similar to L21-30)

Finally, there is a connector designated for
28V DC, designated FSL1, rated for 30A 28VDC,
also a twistlock.

In the entertainment industry, it is common practice to use L16-20 (480V 3phase delta w/ground) for powering chain hoists, and L14-20 (120/250V 1phase w/ground) for chain hoist control connections.
These are run in opposite directions, as a bundled pair of cables. Most of the time,
the motors being used are actually made to run on 208v, not 480, but the connector was apparently chosen to allow for the use of 480v hoists, while maintaining a common stock of cable within the industry.
Since chain hoists are used for overhead rigging, the industry tries to restrict access to the hoists to qualified personel.

I have also seen L14-20 connectors used for control pendants for scissor lifts, etc..

I have also seen various types of twistlock connectors being used for speaker systems,such as L14-20, L1-15, and L5-15, although the industry seems to be moving away from that practice for new equipment.

I do wish that NEMA had created a couple of special and control designations to allow for these uses, without interchanging with commonly used electrical types. Either that, or I wish that the manufacturers had picked connectors that would be highly unlikely to appear in an entertainment venue.

[This message has been edited by techie (edited 07-23-2005).]