Re: Water heater eating X-10 signal

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

In article <84yVh.56915$VU4.35719@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, JeffVolp@xxxxxxx (Jeff Volp) writes:

| Many houses have 240V high-current resistive heating loads (ranges and
| dryers).  The inductance of those circuits would be relatively low, so the
| effect may be more significant than a variety of 120V loads that sum up to
| the same current.

Just to clarify something:  when you talk about the effect of 240V loads
is the concern that they lower the impedance of the whole network as
seen at the repeater significantly compared to the impedance of the
repeater's drivers such that you can observe a lower carrier level at
the repeater itself?

| At first I thought you had a point here, but remember that each neutral goes
| back to the distribution panel common bus.  It doesn't make any difference
| on each of the 120V circuits what the phase is because there is no summing
| together of the return signals on a common netural.

You are ignoring multi-wire branch circuits and sub-panels (themselves
essentially big multi-wire branch circuits).  I don't know whether this
is a reasonable simplification to make in general, but it would almost
certainly not be appropriate for my house which has more than its share
of both.

| Of course, that assumes
| the transmitter is relatively close to the distrbution panel so the summed
| return signals in its own neutral can be ignored.

As long as we are assuming that, it would probably also be reasonable to
assume that we can ignore any loss in the repeater's hot leg connections
along with any losses in the single panel's bus bars, breakers, etc.  With
this model, it appears that the only way a load on one circuit can affect
the signal level on another circuit is by driving the level down at the
repeater itself by presenting a relatively low impedance compared to that
of the repeater's drivers.  This conclusion seems to conflict with my
observations where the level at a repeater can remain constant (high)
while switching a given circuit in and out changes the level seen on
another circuit.  This makes me worry that the model is now _too_
simple. :(

N.B. I'm still very interested in the possibility of a repeater that
drives the legs in phase (especially for use where a blocker/coupler
is required) as I mentioned the last time this topic came up over a
year ago:

http://groups.google.com/group/comp.home.automation/msg/c638afa65ef96d86

But you are going to have to work a little harder to convince me that
ACT/X10/etc. got it wrong for the general case, even if you found their
choice surprising.... :)

| That is true if there is no netural at the 240V X10 load.  Receptacles for
| all our 240V appliances ARE wired with both neutral and ground.  I had to
| buy a new dryer cord for our old Maytag dryer.  I was told that is a NEC
| requirement now.

Electric dryers and most electric stoves are not pure 240V loads; they
are 240V/120V loads and they have always had a neutral.  For many years
the NEC allowed dryers and stoves to ground their chassis to the neutral
in order to save copper (think wartime).  This is why their receptacles
and cords could in many cases be 3-wire.  The exception did not apply if
the appliance was fed from a sub-panel and it never applied in mobile homes,
so happily all existing appliances had to be made to adapt to either 3- or
4-wire hookups.  Recently the NEC removed the exemption for dryer and
stove circuits (in new construction) so now all 240V/120V circuits must
be installed with separate neutral and ground.  You may continue to use
existing 3-wire circuits even for new dryers and stoves.

None of this has anything to do with pure 240V circuits of the type
for which X10 makes modules.  Such circuits never had a neutral and
never will.  See for example:

http://www.x10.com/automation/hd245_s.html

				Dan Lanciani
				ddl@danlan.*com