Re: Water heater eating X-10 signal

[ddl@danlan.*com (Dan Lanciani)]

In article <oK6dnWuv0qmOMLjbnZ2dnUVZ_jadnZ2d@xxxxxxxxxxxx>, mjinks@xxxxxxxxxxxxx (Slammer) writes:

| I am having a hard time with the phrase "in phase" here. Why the worry over
| "the phase of the signal" between different legs of the circuit?

It's germane to the question that started this thread, i.e., why would
adding a leg-to-leg load to an otherwise working system that uses a
repeater induce failure?

| I get the
| feeling you both think the reason that neutral is at 0 volts potential is
| that, the voltage waveforms on each leg destructively interfere with each
| other due to phase cancellation and not simply as a consequence of vector
| addition.

The neutral is often defined as being at 0V potential by convention (and,
pragmatically, because it is usually bonded to a grounding system).  It
really has nothing to do with interference or the vector addition that
can represent same.  In reality, only potential _differences_ are meaningful
and you could just as well choose something other than the neutral as your
0V reference if it makes the analysis easier.  Many X10 modules use a hot
leg (rather than neutral) as their logic 0V reference.  It is convenient to
adopt that convention when working on such circuits since otherwise you
have to deal with Vcc being a 5V DC signal added to the 120V line supply
with respect to neutral.

| As to 240V modules, I'd be surprized if they just didn't listen on one leg
| only,

How exactly would you propose that a 240V module listen on one leg only?
Remember, you can't measure potentials; you can measure only potential
_differences_.

				Dan Lanciani
				ddl@danlan.*com