Questions about programmable switches

[krw]

That's a lot of current for some simple electronics.

No, the return is through the light bulb.

(hot)>>black wire>>(switch)>>black>wire>>(load)>>white>wire>>(return)

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.

[Jennifer Murphy]

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:

"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.

[Tony Hwang]

[Ralph Mowery]

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.

[krw]

Yep. "Be careful".

X10 switches have a slide switch under the button for this.

[Tony Hwang]

Really on a discrete legacy component in 120V AC circuit? Yes if we're talking about IC type component.

[krw]

Yes.

What do you think the switch is?

[Jennifer Murphy]

I found an old Radio Shack (Microndata) Autoranging DMM. The programmable switch controls the porch lights, the yard light, and an outside outlet.

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.

[Tony Hwang]

Hi, 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.....