On Thu, 05 Apr 2012 00:43:31 -0500, wrote:

On Tue, 03 Apr 2012 23:48:53 -0400, wrote:

Geezzzzzz as if that aint enough power!!!! I'd hate to have to pay that
electric bill. And imagine the size of that transformer feeding it.
The biggest listed on that Westinghouse site was 4000 (for low voltage,
meaning 240/120 or three phase 208. I know some buildings have 440 too,
I'm not sure just why, I suppose some motors run on 440, or they split
it into two 220/240 circuits like they do with 240 to 120.

480 generally comes in as wye 3 phase. They use the resulting 277v
line to neutral for lighting
They will have transformers to drop that to 208 3 phase, centertapped
for the 120.

But a centertap on 208 would only result in 104. Or are the centertaps
not exactly centered, and only using the higher voltage half (120 + 88
volts)?

The centertap is 120. It is the centertap of a 3 phase Y transformer.
208/sqr3=120.
The center tap of a single phase transformer is half the voltage.
240/2=120.
As much wiring as I've done, I have never understood how the 3 phase
systems get the desired voltages. Just like how does one get 277v from
480v (half is 240). Then too, why use 277v for lighting? Unlike large
motors and electrical heating sources which are more efficient at higher
voltages, lighting is one thing that surely does not need higher
voltages and would require special bulbs, ballasts, and probably
switches too. Seems sort of pointless....

480/sqr3=277 It is not a center tap of a single phase like 240/120

Higher voltage means less amps for the same amount of power. With
less amps you can use smaller wire and smaller raceways. Since they
use it in most large buildings you can bet it is not pointless.