[Amps] AC wiring

[KD7QAE]

Per the comment below on power supplies drawing non sinusoidal current, 
almost all modern computer power supplies are now switch mode types and 
draw pure sine wave current in phase with the voltage.  This is due to 
the use of active power factor correction which was mandated in world 
trade power supplies in order to avoid neutral heating in building 
circuits not designed for the massive influx of PCs and work stations 
they were seeing in the 1980s and also to prevent the transformers in 
those buildings from having to deal with high circulating currents.  A 
wonderful side benefit is that with a 97% efficient active PFC stage, we 
can now draw full POWER from the wall socket and not be limited by an 
abnormally high RMS current due to the C input filter design.  I know we 
all love those Peter Dahl xfmrs cause they are BIG and SIMPLE, but a 
well designed switcher is a better way to power an amp if you want to 
optimize wiring, size & weight.

IMHO, of course

KD7QAE

R.Measures wrote:

>On Oct 19, 2005, at 7:54 AM, Jim Brown wrote:
>
>  
>
>>On Tue, 18 Oct 2005 20:21:39 -0400, Bill Coleman wrote:
>>
>>    
>>
>>>Seems to me that 12.3 A and 13.4 A are both less than 15 A. So a #14
>>>circuit seems adequate for your example.
>>>      
>>>
>>Yes and no. Remember that ALL electronic loads (that is, anything with 
>>a
>>DC power supply) utilize some form of rectifier and capacitor-input
>>filter. This includes switching power supplies.
>>    
>>
>
>Resonant-choke DC filters are now forbidden?
>
>  
>
>>Thus current draw will
>>be concentrated at the peak of the waveform, and will tend to be quite
>>non-linear. So will the IR drop in the wire. And, because the current 
>>is
>>rich in harmonics, IZ drops can enter the picture.
>>    
>>
>
>I x Z drops enter the picture at 60Hz.
>  
>
>>What does this mean in practical terms?  It simply means that the sag
>>due to loading will be greater than predicted by simple RMS 
>>calculations
>>assuming sinusoidal 60 Hz current flow. Bigger copper will reduce that
>>drop (but not change the fact that the current will be non-sinusoidal).
>>The non-sinusoidal current flow causes distortion of the 60 Hz sine
>>wave, so bigger copper will reduce that distortion and that drop.
>>
>>Last year I wrote a "white paper" on power systems for audio
>>professionals. It addresses this issue as well as many others.
>>
>>http://audiosystemsgroup.com/SurgeXPowerGround.pdf
>>
>>Jim Brown  K9YC
>>
>>
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>>
>>
>>    
>>
>
>Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
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>