On Fri, 17 Feb 2006 11:20:56 -0600, Bud--
wrote:

BP wrote:
The semantics here are getting garbled: If one of the switches on the duplex
device works a light along with another switch located somewhere else, that
is a 2-way function. A 1-way switch has two screws (poles, lugs). a 2-way
has 3 screws, a 3-or-more-way has 4 screws (all assuming only one switch on
the device, not duplex).
HTH


That is eminently reasonable but in the US 2 switches controlling a
light from 2 positions uses 3-way switches with, as you said, 3
terminals each.

Control from 3 or more positions uses 2 3-way switches plus as many
4-way switches as needed. As you said 4-way switches have 4 terminals.



A good reason to learn and use the technical terms "pole" and "throw".

A pole is how many switch-arms a lever controls, and a throw is
how many different contacts that arm can reach.

So a SPST (SIngle-Pole-Single-throw) is 1 circut, either
open, or closed. a SPDT is what most people call a two-way,
where you have one in (or out) selecting between two outs
(or ins). A DPDT is the one that confuses people...
Many modern ones apparently only have four terminals
on them, and are straight-through if the switch is one way,
and crossover if it's the other. The ones I learned on
had six terminals, one at the base of each switch-arm,
and four more at the top and bottom, which means on one
hand that you can use them for anything, but on the other
hand, it always takes me 15 minutes with graph paper
to figure out how.