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From: dgc@math.ucla.edu (David G. Cantor)
Newsgroups: comp.dcom.telecom
Subject: Re: Interested in "Home Switch" for Electrical Instead of Phone
Message-ID: <14929@accuvax.nwu.edu>
Date: 23 Nov 90 02:26:57 GMT
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X-Telecom-Digest: Volume 10, Issue 843, Message 4 of 9


In TELECOM Digest, Volume 10, Issue 841 Joe Konstan asks for:

> An electrical control system for a home to allow [inter alia]
> in a home being rewired ... dynamic (probably computer
> controlled, though hard jumpers would be an alternative)
> changes to a house wiring to alter which lights and outlets
> are controlled by which switches.

Such a system, which also has remote control capabilities, already
exists.  It is called X10 and is available at places like Radio Shack,
various Building supply centers, etc. A commercial, but completely
compatible version, with many more and higher quality devices is sold
by PCC (Powerline Control Components) of Advanced Control
Technologies, Inc.800-229-7878, in Indianapolis, Indiana.  PCC used to
be a subsidiary of Leviton, Inc.

Signalling is done over the power lines, using 121 kHz signals super-
imposed at the zero-crossing of the 60 Hz power.

It provides for up to 256 "devices".  An rs232 connection is
available, and a computer, so connected, can do a variety of things,
including all of the obvious controlling and also signal translating
(this can be used to efffectively change the device a switch
controls).  X10 supports dimming, relays, individual circuits and
switches for one, two, or four devices as well as controller boxes
with support for four, eight, sixteen, and 256 devices, etc. Remote
controllers (both infrared and radio) are available.  Both hard-wired
and plug-in devices are available.  Devices are available for 120
volts, 208 volts and 240 volts.  For the most part prices are quite
(in my opinion) reasonable.

It's primary weakness is security.  As it comes, any controller on the
same power secondary (e.g., one operated by the neighbors' children)
can talk to a device.  When rewiring, as in this situation, the
solution is simple: Insert a 1-1 isolation transformer between the
electrical panel feeding the circuits to be controlled and the main
power in.  This completely isolates the X10 devices.  Note that it
isn't necessary to put the really heavy loads on this transformer.
Heating, drying, electric stoves and ovens, etc. can be fed from
another panel, not so isolated, and be controlled, if necessary, by
relays powered from the isolated panel.  In any case, such isolation
for sensitive circuits is not a bad idea in any home!

For many years, I have used such a system, in a small way, to control
all of my computer components (i. e., my laser printer, my various
external disk drives, etc.) and it has worked well.  I don't have the
usual mess of power cords going to a central switching point.  Each is
plugged into a plug-in control-relay plugged into an outlet near the
device.  In this case isolation is provided by power-line lowpass
filters (also sold by PCC).  I connect two isolated lines (on
different circuit breakers) using a 1 microfarad, 600 volt capacitor.


David G. Cantor    Department of Mathematics  University of California
Los Angeles, CA 90024-1555                Internet:  dgc@math.ucla.edu