4-way switches (was Re: New monitors on old machines)

Tom Watson sdc695 at yahoo.com
Thu Nov 9 13:47:35 CST 2006

der Mouse <mouse at Rodents.Montreal.QC.CA> said:
> >> 7) Three way switch at the other enough of the hall.
> > It's already on a three-way switch with the bottom of the stairs...
> > do they make 4-way switches?
> Yes.  You need two SPDTs (which you already have) plus as many DPDTs as
> necessary to fill out the desired quota of switches (which means just
> one of them, in your case).  I've seen it done (at least for three
> switches).

House 4-way switches DO exist.  They have 4 terminals (thus the [USA/NEMA]
"4-way" designation).  They preform the "normal"/"cris-cross" switching
function.  A quicky web search <"4-way" switches> got lots of answers, and you
can buy these (new, sorry not 10 year old) devices.  The first return from a
yahoo search has a nifty animation on how this all works.  The technology has
been in use for quite some time (the house I grew up in used a 4-way switch in
the 50's).  The problem is that not many places stock the things (I looked on
Home Depot's site to no avail).  Basically the switch train is a bunch of
exclusive-or's so that any switch can make the "sum" 1 (on), or 0 (off).

I had to get a computer reference in there somewhere!

If you do decide to do some wiring, be careful.  There are lots of references
on the web on the "how-to" aspects.

Ob antique stuff:  Yes, the house also (the part built in 1946) had knob & tube
wiring.  The other part (built in 1952) where the 4-way switch was had
something resembling romex.

Tom Watson
tsw at johana.com

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