Re: Want to move to all 208V for server racks

[Kevin Day <toasty () dragondata com>]

On Dec 2, 2010, at 11:06 AM, Owen DeLong wrote:
> It is not uncommon for three-phase panels to be different and have
> all three phases in the panel each phase feeding every third breaker
> slot.


I was just recently trying to explain this to a European friend who thought I was hallucinating this system, so I took 
a picture.

http://dl.dropbox.com/u/230717/temp/208YPanel.jpg

That's a picture of one of the breaker boxes in our office, showing what you described.  There are 3 phases coming into 
the panel, each a different coil off a Y transformer, as well as a "neutral". Those are the 4 black wires you see at 
the bottom. You can see how the three hot phases are staggered as they go up the breaker rails.

For standard 110V service, you use a single-wide breaker and send one hot phase + neutral and you get 110V. The 
difference between two phases is 208 volts though, so you use a double wide breaker and can send to device without 
using a neutral wire. Just 2 hots and a ground. If that's all you're doing (you don't need legacy 110V service 
anywhere) you skip the ground wire going into the panel entirely.

-- Kevin