On Apr 4, 10:43*pm, 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)?

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....

To better understand 3 phase, use a phaser diagram. Draw a circle and
from the center outwards draw three lines to the circle's edge each
line is 120 degrees apart. Now you have a circle with what kindof
looks like a peace symbol.
Each line represents a phase of AC power. Now spin the wheel
[mentally] at 60 Hz and view from the circle's edge watching the TIP
of each line go by. As a function of time, each line will subtend a
sinusoidal waveform. Each waveform is what the 3 phase poer is
doing.

Now you can strt to play gaimes. What would be the voltage if the
three wires were connected between each line tip? What would be the
voltage if you measured from the tip to the center? etc etc. You will
notice that no matter which connection you make the waveforms will
always be 120 degrees apart.