[geeks] New Intel Atom-based barebones system

[Geoffrey S. Mendelson]

On Wed, Aug 20, 2008 at 09:34:22AM -0500, Lionel Peterson wrote:

>At $WORK we just finished rebuilding our data center (6 full size Dell racks, with three relay racks and two Symmetra cabinets), and when we went to put the racks back in place (after re-running all the power lines), we were suprised to find that half our servers were running on 220V, not 110. Auto-switching PS worked out great, allowed us to save on PDU hardware, but it was a bit of a suprise.
>
>$WORK is in USA, BTW.

That's because most people don't understand the electrical system in the U.S.
It's really a 240 volt two phase system with the center tap of the transformer
grounded.

At the entrance to your building, there is a "neutral" connection connected
to ground. At that point it's the same as the saftey ground, but by law
they must be seperated beyond that point.

So what you get at the outlet is one phase and neutral which is 120 volts
(nominally, it's spec'ed at 127). You can also get an outlet that is
both phases (240 volts). They are usually used for high current devices
such as air conditioners, stove tops, ovens and dryers.

In commercial instalations, you often see a 240 volt double phase line
run to a sub panel, where it is split into two 120 volt phases. 

At one time 240 volt appliances used 120 volt timers, with the saftey ground
wire being used as the 120 volt neutral return. That is now illegal, and
a US appliance that uses 120 and 240 volts needs a four pin plug.

Geoff.


-- 
Geoffrey S. Mendelson, Jerusalem, Israel gsm at mendelson.com  N3OWJ/4X1GM