Sounds like it is SS type switch like SCR. Without proper load creating
enough current flow the gate can't trigger to make the
switching device close(conduct. Think in terms of electronics, not
electric/mechanical. Read up on things like SCR, TRIAC, DIAC, DIODES,
opto electric Darlington switch, etc. On the other hand some of those
kinda switches always have residual current flow even if off state.
Use that switch on CFL light, you will see it just dims when turned off.
On Tuesday, December 10, 2013 2:55:12 PM UTC-5, Tony Hwang wrote:
f you only have a 5 watt bulb the current flow would be too low to generate
the needed voltage at the switch. Read about resistors in series if you a
re really interested in the physics and consider one of the resistors the s
witch and the other, the light bulb.
That's not the issue.
The timer uses the line through the load to operate it's clock because it h
as no neutral. If the load is missing or not enough the clock doesn't work
properly. 5 watts is plenty of load for a scr or triac.
On Tuesday, December 10, 2013 4:54:21 PM UTC-5, Tony Hwang wrote:
if you only have a 5 watt bulb the current flow would be too low to genera
te the needed voltage at the switch. Read about resistors in series if you
are really interested in the physics and consider one of the resistors the
switch and the other, the light bulb.
it has no neutral. If the load is missing or not enough the clock doesn't
work properly. 5 watts is plenty of load for a scr or triac.
It's plenty of current to run the clock/timer/lcd electronics in the
programmable timer. How much current does it take to run
a digital watch?
If there is no
When the switch is off, it relies on the path through the load,
to the neutral, to complete the circuit. That's why the load has
to be at least 40W, or whatever the number was.
That's a lot of current for some simple electronics.
No, the return is through the light bulb.
It's on the other side of the load. There is always current through
the load. When changing light bulbs, be careful with these because
the lamp is still energized with it turned off.
X10 switches work this way because there is no guarantee that there
will be a neutral in the box. Insteon devices don't and require a
neutral to operate.
On Tue, 10 Dec 2013 19:12:05 -0500, email@example.com wrote:
The Honeywell PLS550A has a little "safety switch" just under the main
button that can be pulled out with a fingernail to cut power to the
switch (and load) when changing a light bulb. See this image:
This page has the spec sheet / instruction manual / user guide:
The text under the safety switch says:
"Safety Switch: Before replacing a light bulb, pull out to disconnect
power to the switch. This prevents, while the bulb is out, any possible
short circuit which will damage the switch. Push back in after the light
bulb is replaced."
I'm not sure whether the "safety" is for the switch or for the user.
What would happen if I inadvertantly touched the two leads in the light
socket with the switch in the "off" position? Could I feel the current?
I had the predecessor (Ti034), which did not have the safety switch. I
changed the bulb a few times and never had a problem.
The safety switch is to totaly disconnect the load from the switch. It is
for the person doing work on the wiring after the switch. It is not for the
protection of the switch, but could protect the switch if the wires were
shorted to each other on the load side.
As mentioned before the operation of the switch depends on a small ammount
of current passing through the switch. Not enough to ammount to anything
cost wise, but enough to give you a shock.
For just replacing a light bulb, that is not a problem, just don't sick your
finger in the socket.
On Tuesday, December 10, 2013 2:38:00 PM UTC-5, jamesgang wrote:
you only have a 5 watt bulb the current flow would be too low to generate t
he needed voltage at the switch. Read about resistors in series if you are
really interested in the physics and consider one of the resistors the swi
tch and the other, the light bulb.
Another simpler way of looking at it is the thermostat needs a path to
a neutral. A 1000W load is a low resistance and closer to being directly
connected to a neutral than a 5W load.
On Tue, 10 Dec 2013 09:54:20 -0800 (PST), " firstname.lastname@example.org"
I found an old Radio Shack (Microndata) Autoranging DMM. The
programmable switch controls the porch lights, the yard light, and an
With the switch turned OFF, the DMM shows about .035 volts across the
contacts in the outlet. With the switch ON, it shows about 117 volts.
Then I unplugged the Christmas lights and unscrewed all of the porch
lights. When I unscrewed the last one, the switch went dark. It cannot
operate with an open circuit. It needs at least a small load to work.
What I didn't think to try, was screwing in just one bulb of less than
40 watts to see if it could still work. If I remember, I'll do that when
I take the Christmas light down.
So, it looks like you were right. But then you already knew that. :-)
And, I guess they can continue to teach E=IR in high school physics.
Nothing wrong with E=IR. You have to expand it to accommodate solid
state devices, Also DMM is highly sensitive due to high input impedance.
If you measure the voltage with analog meter, reading probably is
negligible. Lot of modern devices have phanotom current flowing all the
time. TV, stereos, desk top PCs, etc. what have you are on stand-by. TV
won't come on if you unplug the set when you push remote button.....
It needs a minimal load. It will not be dammaged, but may not work. It is
using the load on the end to get a sort of 'fake neutral'. The switch is
getting the incomming power from the hot wire. As there is no neutral in
the box, there must be a return path so a small ammount of return power goes
through the load. Not enough power will go through it to light a 40 watt
light bulb, but some power is. Probably enough to give you a shock if you
touch the load side of the switch even if the light is 'off '.
On Mon, 9 Dec 2013 11:36:37 -0800 (PST), jamesgang
The outlet is only about 10 feet from the switch box as the crow flies,
but it goes under the porch or over the front door. The existing wiring
is from the 1940s, at least some of it. One of the lines coming into
that switch box is fabric covered. I think fishing a line would be
impossible, at least for me.
But doesn't the neutral have to go back to the circuit breaker? That's
clear at the back of the house.
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