OT Voltages

[J. Larry Hendry]

----------
> From: D. Schouten <daniels at xs4all.nl>
> 
> This is because the secondaries of the local grid transformer are
connected in a
> socalled Wye configuration with the neutral conductor connected in the
star
> point. The 400V voltages are present relative on the exits of this Wye
(=Y),
> while the line voltages of 230V are present on these exits relative to
the
> neutral.

Exactly.  This is a common connection in the US also.  The primary to
secondary step down bank voltages (in a three phase installation) here are
normally 120 volts connected wye (or star as some call it).  So the phase
to ground voltage is 120 but the phase to phase voltage is 208 (1/2 of your
240/415).

The same arrangement is common at 480 / 277 volts connnected delta / delta
instead of delta / wye here in the US.  These voltages are normally used
for commercial applications.  Often times the 480 volt delta is left
completely ungrounded so that a single phase to ground fault can be sensed,
tolerated, and repaired without loss of load.  Other installations ground
one leg of the delta.

Lastly, and I will cease this OT thread:  The answer concerning three phase
in the US is no.  It is rare for a residence to have three phase power.  It
is common for larger loads to have three phase.  
 
Thanks to those that responded.
Larry Hendry