At 06:43 PM 5/16/2014, Gnarlodious wrote:
>Modern homes have 2-phase service to run resistive loads like clothes
>dryers or water heaters, which use a special huge socket. The service box
>is 2-phase but wired for single-phase loads. Except for the dryer and oven,
>which tap across 2 phases. You won't find any large inductive loads in
>residential homes

Ok, we're talking about the same thing but disagreeing about what to
call it.  I really don't see how it's legitimate to call the output
of a single transformer winding "two-phase" if you're not using the
center tap, as you are not when you hook up 220V loads in US domestic
service.  Suppose that instead of grounding the neutral wire you
grounded one of the hot wires.  Now it would stay at earth potential
and you'd have a 110V hot from the center tap and a 220V hot from the
other end of the winding -- both exactly in phase.  But leaving aside
the practicalities of safety making this arrangement undesirable, you
haven't actually changed anything.

I think "split-phase" is a useful way to describe how we wire houses
in the US, and "two phase" is not; especially when there are actual
two-phase systems still in use in this country.

Yours,
David