July 1966 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
I have to laugh a bit when seeing
this article on how to wire up a set of 3-way switches "[i]f you only have a two-wire
cable to work with." There have been many times when I needed to wire a set of 3-way
switches and only had 2-wire Romex cable on-hand. The simple solution is to simply run
two pieces of 2-wire cable and only use one wire from the second piece. A 250' roll of
14-3 w/ground costs about $79 at the hardware store. A 250' roll of 14-2 w/ground costs
about $45. For short runs, the additional cost of using two pieces of 14-2 compared to
a single piece of 14-3 is diddly. However, if you want a more elegant, high-tech solution
and don't mind paying for some diodes (that might fail), here are two ways of accomplishing
your goal. I don't recommend it, though.
Two-Wire, Three-Way Switching Circuit
By R. C. Hitchcock and G. E. Weber
Mag Tag: p.88 Work it out. Always be hot or neutral switches
Two four-way switches (d.p.d.t.) and two diodes wired back-to-back
in a two-wire circuit provide three-way light control. If the light stays on regardless
of switch position, reverse one of the diodes.
Two three-way switches (s.p.d.t.), four diodes, and two wires also
enable three-way switching action. Observe polarity. Different switch manufacturers may
locate and wire switch terminals differently.
If you only have a two-wire cable to work with, you can still hook up a three-way
switching circuit for your garage, or hallway, to enable you to turn a light on and off
from either of two different locations.
For a dollar or two, you can purchase a couple of four-way light switches and a couple
of silicon diodes (1N1344, 1N1614, or equivalent) and connect them as shown in the diagram
below. Observe the usual precautions to avoid short circuits, and do your switching in
the hot lead; do not break the ground lead. If you prefer to work with three-way switches,
you can, but you'll need two more diodes.
Since the voltage available at the lamp is reduced from 117 volts to about 83 volts,
you'll get a little less light but a lot more life out of the light bulb. To get more
light, simply use a higher wattage lamp, but do not exceed the wattage and current ratings
of the diodes.
Posted April 19, 2018