In article , Wayne Whitney wrote:
On 2005-03-20, Doug Miller wrote:

In article , Wayne Whitney
wrote:

It does seem true that sharing a neutral between the two circuits on
separate legs reduces the voltage drop due to the wiring. The current
on the neutral leg is less than on either hot, so the voltage drop due
to the neutral leg is less than it would be with a separate neutral.

Irrelevant. This would do nothing to alter the voltage drop between the
supply
and the load, which is the only place it really matters.

I don't believe that is correct. Given a fixed voltage available at
the panel, and for example a resistive load, the hot and neutral wires
are effectively resistors in series with the load.

Yes, that's true, but you're talking about resistances measured in tenths of
ohms, in series with resistances measured in hundreds of ohms. As a practical
matter, except on *very* long runs, the resistance of the conductors is not
really a concern.

The total
resistance of the circuit will be the resistance of the hot +
resistance of the load + resistance of the neutral. You can't ignore
the neutral just because it is after the load.

I'm *not* ignoring the neutral. But you're missing the fact that the voltage
drop between the source and the load is almost completely independent of the
resistance *elsewhere* in the circuit. The only effect that the resistance of
the neutral has on the circuit is a *minuscule* difference in the current that
flows through it.

Another way of looking at things is that using a shared neutral makes
the overall circuit partially parallel, and two resistors in parallel
have a lower resistance than they do in series.

The effect on voltage drop is still so small as to be utterly negligible.

Further, the resistance of whatever load is applied to the circuit,
even if it's just a single light bulb, is orders of magnitude
greater than the resistance of the conductors.

Well, this is always true, yet on a long run conductors are typically
oversized to avoid an excessive voltage drop. So it does happen.

Do you know just *how* low the resistance of copper conductors actually is?

Admittedly the benefit of reduced voltage drop due to a shared neutral
may be more theoretical than of practical importance, but I do believe
it is real.

I don't think I ever said it wasn't "real". But it certainly isn't important.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?