Questions about programmable switches

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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 switches.
The 540A:
http://www.honeywellstore.com/store/products/honeywell-econoswitch-programmable-light-switch-timer-white.htm
and the 740B:
http://www.honeywellstore.com/store/products/honeywell-econoswitch-7-day-solar-programmable-light-switch-timer-white.htm
The 540A is similar to the one I've had for 10 years that was fried:
http://www.aubetech.com/products/produitsDetails.php?noProduitu&noLangue=2
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 compressor motor.
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 candelabras?
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?
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On 12/09/2013 10:51 AM, Jennifer Murphy wrote:

If the load is under 40 watts, the unit will not get damaged, it simply may not work.

It looks like it just connects to a standard three prong receptacle and does not require any special wiring.
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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 I'd ask.
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On 12/9/2013 2:11 PM, Jennifer Murphy wrote:

So you have hot and ground, but no neutral? Man, that's some kind of messed up house. Every house I've seen had hot and neutral, but maybe not a ground.
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On 12/9/13, 6:58 PM, Stormin Mormon wrote:

Chris, Chris,
The switch box has no neutral available. Not the house. See this diagram http://www.photocar.org/wiring-diagram-light-switch.html/wiring-diagram-light-switch-34038
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On 12/9/2013 7:12 PM, Retired wrote:

Thanks, that sure makes things a LOT more clear. The diagram is a big, big help.
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<snip> >>

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.
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Or "junction box"? Or is that a closed box?
What's a receptacle? Or did I make that word up?

Thanks
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On 12/09/2013 02:04 PM, Jennifer Murphy wrote:

OK sorry, I did not take a close look...I thought it was a plug-in device.
I guess I'd Google for a programmable switch with neutral not required
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On 12/9/2013 4:56 PM, philo wrote:

How would run any 110VAC or 120 VAC device, and not have a neutral? Don't think that's ever been done.
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On 12/09/2013 06:07 PM, Stormin Mormon wrote:

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 the bulb.
It would be against electrical code to use the ground wire (green) as a return.
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On 12/9/13, 3:04 PM, Jennifer Murphy wrote:

Generically it is a "switch box", like this: (Amazon.com product link shortened)
but can contain a "receptacle", which is otherwise called an "outlet"

Yes, Junction boxes" are just that, where just cables are spliced together. Like this: (Amazon.com product link shortened)

Here is a receptacle: (Amazon.com product link shortened)
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Thanks for the tutorial. Amateurs are notoriously lax with terminology. :-) I be more careful in the future. I got "short" and "open" mixed up a few weeks ago and I actually know the difference there.
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On 12/9/2013 3:04 PM, Jennifer Murphy wrote:

Picture of receptacle:
http://hostedmedia.reimanpub.com/TFH/Projects/FH10JUN_OUTLET_02.JPG
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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.
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On Tue, 10 Dec 2013 05:45:31 -0800 (PST), " snipped-for-privacy@optonline.net"

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 flowing), right?
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said it needed was actually 40W.

With a regular on/off switch, no current will flow when off if it is operating properly.
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 loades either.
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.
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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.
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On Tue, 10 Dec 2013 09:54:20 -0800 (PST), " snipped-for-privacy@optonline.net"

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 watt.
I should have paid closer attention in freshman physics.
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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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