On Sat, 12 Jun 2004 17:18:00 GMT, "Alan Black" wrote:
Hi Gary,
I have had no personal experience with wiring a 2 phase system, but my
"American Electricians Handbook" Eleventh edition Page 3-10, Fig. 3-23, Fig
17 shows 2 phase, 4 wire as two separate single phase circuits 90 degrees of
phase apart. You are correct in that it does not call one of the conductors
in a single phase two wire circuit a "neutral" either (Fig. 14)
But in the diagram there is no "voltage relation" between the two pairs.

The diagram may not show it, but there is a definite voltage relationship between
each of the wires. They're orthogonal to each other, so going around the diamond
clockwise, each adjacent set of wires has a voltage magnitude between them which
is sqrt(2)/2 the pair voltage across each phase pair (polarities at any given snapshot
instant swap as you move from quadrant to quadrant, of course).

So possibly using the term "neutral" on my part was not technically correct
unless it is a accepted term to describe one of the conductors of a single
phase circuit. In either event it seems that you can switch a 2 phase, 4
wire, circuit with two poles as it would interrupt each of the pairs
satisfactorily.

Neutral is a term used to describe a conductor about which all other voltages
in the system are symmetric. The term fits for the centertap in a single phase
240 volt residential system. It also fits in a 4 wire 3 phase wye system. But the
symmetry point doesn't have a wire in a 3 phase delta system or in a 2 phase
4 wire system. So there is no neutral. All conductors are hot with respect to
each other, and are at some undefined potential with respect to Earth.

In a residential system, neutral is bonded to Earth at the entrance panel. So
it is safe to not interrupt it when you switch a 120 volt circuit. But the other
systems don't have any of the wires bonded to Earth (there are exceptions to
this such as corner ground delta, but I'll ignore the exceptions here), so it is
necessary to switch all the hots in order to assure the circuit is cold, ie if you
were to want to work on the wiring downstream of the switch, for example.

After all the discussion fun as it is, of greater curiosity is why have
we have not heard a peep from Dan Miller, the original poster of the
question?

Well, hopefully he didn't fry himself.

Gary