> Wye doesn't have to have a center tap to neutral if the phases are loaded
> correctly.

By definition Wye has a central neutral from which each of the phases are
measured. If the phases are exactly balanced there will be no current
through this connection, but that seldom happens.

With Delta, I don't know what you mean by "center tap of one
> phase."  And I definitely wouldn't connect any phase to neutral on delta
> unless you like to see a lot of sparks.  A direct connection to ground
like
> that will probably blow apart your whole fuse box and take you with it.

The secondary of a transformer wired for Delta output can be wired in any of
three ways:

1: Floating - often used in manufacturing plants so that any was phase can
'ground out' without causing a hazard or lots of sparks. In this case you
can connect a light bulb from each phase to earth ground and they should all
glow equally bright as long as you do not have a phase fault. If a phase is
grounded the corresponding lightbulb goes out and the other two reach full
brilliance.

2: Corner neutral. One of the three phase points becomes the neutral and
grounded voltage.

3: Midphase neutral. The midpoint between two of the phases becomes your
neutral/ground. This is sometimes done to obtain 110/220 circuits from a
delta circuit.

Bob Ammerman
RAm Systems

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