[Elecraft] [OT] NEC wire size requirements

[Jim Brown]

On Thu,8/11/2016 12:03 PM, Lewis Phelps wrote:
> So, why go to the extra expense of #6 wire?

All the calculators assume sinusoidal current (i.e., a perfect 60 Hz 
sine wave). That's not the real world -- only un-controlled heating 
elements draw sine wave current. For at least the past 30+ years, 
electronic loads dominate, and the what's connected to the power line is 
a transformer-rectifier-capacitor power supply, and now usually as the 
input to an SMPS. The line current drawn by such a supply takes the form 
of short pulses at positive and negative peaks of the 60 Hz waveform, so 
both IR drop and dissipation is much greater than predicted by simple 
sine wave analysis. None of this is taken into account by NEC.

Thus, it IS good engineering practice to oversize AC conductors.

There's a tutorial discussion of this in

http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC