I need to replace a programmable light switch that was fried when a
contractor plugged a compresser into the outlet it controls. I am trying
to decide between these two Honeywell (Aube) programmable sunset/sunrise
and the 740B:
The 540A is similar to the one I've had for 10 years that was fried:
It is designed to replace a standard toggle switch. The problem is that
it can only handle 500 watts, which is why it was fried by the
It also requires a minimum load of 40 watts. Why is that? Why would it
be damaged if the load were just a 25 watt bulb or a few 5 watt LED
The newer model above (540A) has a little safety switch on the front to
cut power to the switch while changing light bulbs to prevent a short.
The 740B has a limit of 1800 watts and no minimum, but it requires a
neutral line. The receptacle where I want to put it has just three
wires, which I think are the line (hot), the load (lights), and the
ground (bare wire).
Is there any way to use the 740B in that receptacle?
Well, maybe not *special* wiring, but it does require a neutral, which I
do not have in this old house. So my question is whether there is any
way to use the 740A, which says it requires a neutral, in a receptacle
that does not have a neutral. I assume the answer is "no", but I thought
Jennifer, you say "receptacle", but you mean "switch box".
Philo, the 740B replaces a standard light switch. It needs a neutral.
So if the Switch box onlys has 3 wires as Jennifer described ( the
white is a switched "black", not a neutral), then a real neutral would
need to be pulled in.
In a switch box there would not normally be a neutral wire...
there would be a (black) "hot" and the other wire is the one going to
It would be against electrical code to use the ground wire (green) as a
On Monday, December 9, 2013 3:04:19 PM UTC-5, Jennifer Murphy wrote:
It's an outlet that you plug things into.
If the box has no neutral, then there is no code compliant
way to make the switch that requires it work. The issue is
that a programmable switch needs to be powered somehow. That
could be by a battery, through the hot and neutral, or by
using the load circuit. The latter is why the other switch
has a minimum load of 25W. Without some kind of minimal load
for a small current to flow through and power the switch even
when it's off, it would have no power. That small current flows
through the bulb when off and it's enough for thw switch, but
so tiny it won't light the bulb at all.
On Tue, 10 Dec 2013 05:45:31 -0800 (PST), " email@example.com"
The minimum it said it needed was actually 40W.
Does the switch really draw 40W for its own use? That seems like a lot
for a small electronic circuit. It does have an LED screen that could be
on Hi all the time depending on user settings. I have mine set to dim
after 8 seconds.
With a regular toggle switch, off is an open circuit (no current
With a regular on/off switch, no current will flow when off if it is
The programmable switch has to have a connection through the load back to
the neutral of the AC power. It will take a certain ammount of a load to
provide that. Some loads like the new CFL or LED bulbs may not work as
The programmable switch doen not draw 40 watts , but much less maybe a watt
or two or even less.
If it drew much power at all and you put an old filiment light bulb as the
load, it would glow maybe a dull red. I doubt you would see anykind of glow
at all with the switch in the off position even though a small ammount of
current will be flowing.
A 60 watt bulbs takes about 1/2 of an amp or 500 ma. On dry skin you can
feel about 1 or 2 ma. Get up to around 50 ma and it can be painful. Much
more and maybe death.
On Tuesday, December 10, 2013 11:30:17 AM UTC-5, Jennifer Murphy wrote:
No, it draws negligible amount of power. If it drew
40W the box would over heat. It's just that with no
neutral, the switch winds up getting it's power in
series with whatever the load is. With too small of a
load, the switch can't get the necessary voltage/current
that it needs.
That seems like a lot
Yes. And with one of those other prog switches that use a
neutral, the tiny current to power the switch electronics is
flowing from the hot, throught the switch, to the neutral.
So, with those the line going to the light is open too.
With the switches that don't require a neutral, with the
switch off, you still have that tiny current flowing from
hot, through switch, through load, then to neutral at the load.
On Tue, 10 Dec 2013 09:54:20 -0800 (PST), " firstname.lastname@example.org"
If the switch obnly needs a fraction of a watt to operate, why does it
say that the load must be at least 40W? Why couldn't it get ebnough
power with a 5W bulb as the load. 5W is much larger than a fraction of a
I should have paid closer attention in freshman physics.
On Tuesday, December 10, 2013 1:24:28 PM UTC-5, Jennifer Murphy wrote:
The switch is in series with the load, in this case a light bulb. So if yo
u 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 are r
eally interested in the physics and consider one of the resistors the switc
h and the other, the light bulb.
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