According to Jeff Wisnia :
CWLee wrote:

Perhaps I mislead you earlier; let me clarify. The reading
of about 50 volts was not done with the bulbs as a load.
The house circuit was wired to the switch, and then the
leads from the voltmeter were attached to the output side of
the switch. At the time the switch was not mounted to the
housing, but rather suspended in air from the house wires.
Then the toggle lever was moved and readings noted.

We have not tested to see if the bulbs are warm after
several hours in the OFF position. That sounds like a good
test, and we have considered it, and will eventually do it.
Because of other wiring and construction going on in that
part of the house, requiring that certain circuits remain
shut down, it has not been practical to perform such a test
yet. I'll keep you posted on any new developments. If the
additional information provided in this post gives you
further insight, please share it.

snipped my previous blatherings...

I'd bet what's left of my virginity against a cigarette butt that if you
make the voltage measurement you described WITH the bulb loads connected
you'll see the voltage goes to zero when the slider is all the way down.

That 40-50 volts you measured was a "phantom" voltage developed by
miniscule leakage currents, too low to even fry a mosquito, flowing
through the megohms high input impedance of your voltmeter.

It is _extremely_ misleading to measure the output voltage of a
dimmer with a high impedance meter (eg: DVM) with no load (eg:
a bulb) attached. Especially cheap DVMs. Even when a load
is connected, it will be somewhat misleading.

A dimmer operates by chopping up the waveforms. Which means a lot
of "off state", which can show as relatively high voltage unless
it's loaded. Secondly, unless it's a true integrating DVM, voltage
measurements are somewhat meaningless on chopped wave forms - even
at full dim (but not quite off), the voltage seen by the load is
still peaking at 160V.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.