Trekkie,
Yup, I do think some of the numbers are arbitrary.
Does the 10 foot tap rule offer that much more safety over what could easily be the 11 foot tap rule? :-)
I've also heard the tale that the 6' 7" mounting height for a disconnect handle was based on what the shortest person on the code panel could comfortably reach.
Frequently, when I see a number in the NEC, I wonder what the reasoning was that resulted in that exact number. I suspect that at least a few of them were selected because they were easy to remember.
Tom
