[Elecraft] [OT] NEC wire size requirements

[Matt Zilmer]

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
> wunder at wunderwood.org
> http://observer.wunderwood.org/  (my blog)
>
>
>> On Aug 11, 2016, at 1:09 PM, Jim Brown <jim at 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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Always store beer in a dark place.  - R. Heinlein

Matt Zilmer, W6NIA
[Shiraz]