J Burns wrote:
bud-- wrote:

As RBM wrote "Pilot light switches are lit when the circuit is on, and
illuminated switches are lit when the circuit is off." Both of these
have the light in the handle of the switch (not a separate pilot light).

"Illuminated switches" are easy - as I said before you connect a neon
lamp between the traveler terminals If you work out the circuit, this
is the same as connecting a neon lamp across a single-pole switch.

"Pilot light switches" from Leviton require a neutral connection - I
believe that is true for all of them. They don't use a ground
connection. The circuit for one that I saw had resistors from each
traveler terminal to a common point. A neon lamp connected from that
point to a neutral.

Both of these use current through the load to light the neon lamp. If
a light bulb is burned out they will not work. They may or may not
work with fluorescents (CFLs).


In the Leviton system you describe, suppose R is the resistance of each
resistor in the voltage divider (between travelers). Suppose I is the
current of the neon indicator.

If the load bulb is burned out, the voltage divider will be between hot
and open regardless of switch positions. Voltage across the indicator
should be 120-IR. I would expect the indicator to glow.

If the bulb is burning, the voltage divider will also be between hot and
open. The indicator should glow as above.

If the bulb works but is switched off, the voltage divider will be
between hot and neutral (ignoring the bulb's small resistance). The
voltage across the indicator should be 60-(IR/2). I suppose the
indicator wouldn't light.

Neon lamps are not like incandescents in that the voltage across the
lamp is essentially constant after the lamp has 'fired' (ionized the gas
and started conducting). And if the voltage is not high enough the neon
lamp will not fire on every half cycle.

60V may not be enough to 'fire' the neon lamp. Or, because the neon lamp
is at constant voltage, the drop across the resistors is much lower than
you expect and the current is relatively low - dim neon lamp


So it appears to me that load current is required not to turn the
indicator on but to turn it off.


Sounds eminently reasonable. I was 1/2 wrong.

If the bulb is burned out, (or maybe fluorescent), or switched
receptacle with nothing plugged in the switch won't indicate right.

--
bud--