On Tuesday, December 10, 2013 2:38:00 PM UTC-5, jamesgang wrote:
On Tuesday, December 10, 2013 1:24:28 PM UTC-5, Jennifer Murphy wrote:

On Tue, 10 Dec 2013 09:54:20 -0800 (PST), "



wrote:







On Tuesday, December 10, 2013 11:30:17 AM UTC-5, Jennifer Murphy wrote:



On Tue, 10 Dec 2013 05:45:31 -0800 (PST), "







wrote:















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.







The minimum it said it needed was actually 40W.







Does the switch really draw 40W for its own use?







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.







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.



The switch is in series with the load, in this case a light bulb. So if 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 are really interested in the physics and consider one of the resistors the switch and the other, the light bulb.

+1

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.