Was this a "shared neutral" type of problem? I thought NEC ruled that
out in post-1979 wiring plans.
73,
matt W6NIA
On 8/11/2016 2:10 PM, Walter Underwood wrote:
In the late 1980’s, we had some cubicle wiring fires at HP Labs caused by
computer power supplies. They had to replace all the wiring with bigger
conductors and connectors for the neutral. The same thing happened with Project
Athena at MIT.
wunder
K6WRU
Walter Underwood
wun...@wunderwood.org
http://observer.wunderwood.org/ (my blog)
On Aug 11, 2016, at 1:09 PM, Jim Brown <j...@audiosystemsgroup.com> wrote:
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
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