[Amps] 240V Outlet

[Jim Brown]

On Sun, 09 Aug 2009 12:00:25 -0400, David C. Hallam wrote:

>I need to put in a new 240V outlet at my operating position.  Since one 
>of my amp power supplies, a Johnson 2000 has the low voltage portion 
>operating on 120V, I suppose I have to put in a 3 wire plus ground circuit.

It depends on how the power supply is wired. One good way to get 120 volts 
from a 240 volt circuit is by running that load (typically a cooling fan) 
from half of a center-tapped primary of the main power transformer -- 
PROVIDED THAT THE CENTER TAP IS NOT GROUNDED. A lot of good power amps are 
built this way. 

If the amp needs 120 volts and doesn't do this (and can't be rewired to do 
this), you DO need to bring both 240 volt "phase" conductors, the neutral 
conductor, and the green wire to the shack out. 

Examples of "right" and "wrong" are shown in 

http://audiosystemsgroup.com/HamInterfacing.pdf

Page down to the section where I'm discussing magnetic hum coupling. The Ten 
Tec Titan power supplies are good examples of doing it right. 

Another point. If the conductors you run and the breakers are properly sized 
to handle the loads, there's nothing wrong with having a 240V outlet and 
120V outlets on the same breakers and in the same outlet box. To do this, of 
course, you must use the neutral. This has the great advantage of minimizing 
the noise on ground, which in turn minimizes "ground buzz" when audio is fed 
between computer and your rigs. 

A near ideal power distro for a ham shack would use #12 or even #10 copper 
and 20A breakers and outlets in steel backboxes. Put in enough outlets so 
that all your gear can plug into them without the use of extension outlet 
strips, bonding all of those outlet boxes together (for example, with 
thinwall steel conduit, also known as EMT). If you run SO2R contesting with 
amps, put in two 240V outlets. The only way you would need more power than 
this for radio gear is for a multi-multi contesting operation!  

73,

Jim K9YC