[bpeng]

I encountered the following description of an audiophile's house power:
 
He lives in Canada and says the power into the house is "single phase 120V/240V AC 60 HZ, 3 wire (red, black, white (N) with ground," Is this typical for the United States as well or something peculiar to Canada or other non-US countries? Am I to understand that the voltage between red/white and black/white is each 120V, but between red and black is 240 V?
 
He writes that each of his two systems (2-channel and A/V) has a separate circuit with an isolation transformer with a 240V primary and "120/240V secondary" (not sure why two voltages are given for the secondary--maybe two taps?) He writes that he's using 240 V into the isolation transformer in order to reduce the current draw and reject common-mode noise. Can someone explain in what sense this will reject common-mode noise? Common-mode between what two lines? Or is that not clear?
 
Thanks,
Mike

 

[Speedskater]

Almost all (99.9%) residential power in North America is 'single phase' also known as 'split phase 120/240V'. 
Note that the poles or legs are often misidentified as phases.
 
If you double the line voltage you half the line current. Noise is related to current, so you half the noise also.
 
For more on this, see the excellent Middle Atlantic paper.
 
"Power Distribution and Grounding of Audio, Video and Telecommunications Equipment White Paper"
 
http://www.middleatlantic.com/resources/white-papers.aspx

 

[bpeng]

great link, Thanks!