On Thu, 23 Dec 2004 23:18:38 GMT, "Chuck Hoffman"
wrote:

"Doug Miller" wrote in message
om....

Utter nonsense.

No, it isn't. Look at my simplified description of the current in a
two-phase circuit for a clue that I know what I'm talking about.

Right church, wrong pew.

All the stuff you wrote about phase angle and AC circuits, etc. seems
to be okay, however, you liberally sprinkled in terms that in the real
world of electrical wiring just aren't true. Let's take a look.

There is no argument at all. In a two-wire 115V circuit, the current
carried by the neutral is exactly the same as that carried by the hot wire.

True. You should have stopped there.

In a three-wire 230V circuit, there is a property called phase angle
or J-factor. This results in current flowing in both directions at the same time

I don't recall J-factor in the NEC. That could be me, though.

(this is not exactly a true statement but a convenient way to consider
current flow in a three-wire circuit).

And since it's not, you should have left it alone.

As the current on one phase increases from zero to some positive
value, the current in the other phase is decreasing from its positive
value to zero.

Here's the crux of the problem. In electrical systems (the stuff the
power company provides) current is delivered in three phases. In the
average house, however (and that is what the discussion is about),
power is delivered from only one phase of the three phase system.

It is run through a center tap transformer which yields two "hot" legs
that are 180° out of phase and a common return leg. All three of these
wires, however, are delivered from a single phase.

There is no two phase power. It's either three phase or single phase.
No electrician calls either hot leg a "phase."

The vector sum of the currents on the neutral is exactly the same as
the total of both phases.

Yeah, you could say that...if you wanted to answer the question of
"what time is it?" by telling us how to build a clock.

Because of the phase angle, however, that does not mean twice
the current.

Phase angle, as a concept, is perfectly suited for all sorts of
theoretical discussions but is unnecessarily complex in single phase
wiring. The only "angle" to consider is the 180° that each leg of the
single phase power feed to house is out of to each other.

It never exceeds the total current of each phase individually.

Correct (except for that "phase" thing), but you sure took the long
way around to get to it, and lost half the pack doing it.

Confusing? Yes. One has to study alternating current and understand
plane geometry and simple trigonometry to comprehend it.

Please. Opposite legs have opposite values (because they are 180° out
of phase) and the current is additive. It's simple arithmetic (albeit
incorporating negative numbers).

Sorry...neglected to answer your original question. I believe the NEC
frowns on connecting across one phase of a 230V circuit to get 115V.

Given that stoves and dryers sometimes do that very thing, I believe
you're wrong...unless you could cite the section in which they "frown"
upon it.

That WOULD double the current on the neutral and result in a potential
overload.

This is the part that Doug describes as utter nonsense. And he's
right. The ONLY current on the neutral would result from the
connection across one LEG of the 230V circuit (to get 115V). There is
NO current in the "neutral" of a 230V circuit because there is no
"neutral" in a 230V circuit.


- -
LRod

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Shamelessly whoring my website since 1999

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