Strange behavior of dimmer switch

[David Nebenzahl]

Just installed a replacement dimmer switch that exhibits the same strange behavior as the previous one.

It's on a circuit that's wired correctly. I have a dedicated outlet running a string of low-voltage halogen lights through a transformer. When I installed the first dimmer, it worked fine. When I checked it with my handy-dandy circuit checker (you know, the type with the 3 leds), it indicated the circuit was OK with the power applied. BUT: when the dimmer was switched off, the tester indicated a fault ("open neutral", it said).

So I replaced the dimmer temporarily with a single-pole switch; circuit acted normally with power on and off.

Then I replaced the dimmer (it's a Lutron "decora"-style with the big rocker switch on front and a little slider doohickey). Guess what? Same deal; tester says "OK" when on but "open neutral" when off.

What gives? All I can think is that the dimmer is drawing just enough current when in the "off" position to spook the tester. (Yeah, I know those types of testers aren't 100% conclusive, but shoot, it's better than sticking your fingers on the damn wires.) Why this would be the case, I have no idea.

Although, I just realized: the dimmer packaging says "locator light" on it; is there a dim light on this that is drawing this current? (I'm not at my client's site right now.)

D "puzzled" N

[Steve]

Some of these devices allow a trickle of current to flow through the bulb so they can keep the circuitry energized. X10 switches work this way.

[David Nebenzahl]

Steve spake thus:

But why keep the circuit energized? (This isn't an X10 device.)

[mike.j.harvey]

David, I answered your question about Color Return in sci.electronics.repair.

[John Grabowski]

Forget about your tester. What is the problem with the lights? Are they flickering? Is the transformer making noise? For a transformer load it is usually a good idea to use a dimmer rated for a magnetic load unless the transformer is electronic in which case use a dimmer rated for an electronic load. A locator switch has a small pilot light that is on when the switch is off so that you can locate the switch in the dark.

[jerry_maple]

I put a similar "decora"-style dimmer switch in my bathroom about a month ago, which has a neon locator light. On my switch, there was a small slider switch you can use to enable or disable the locator lamp, it's covered by the cover plate when you put the cover back on the switch. Have you tried switching off the locator lamp to see if that makes a difference?

Jerry

[David Nebenzahl]

jerry [e-mail] spake thus:

Now that I don't know; next time I go by my client's place I'll look at it.

Thanks for the only useful response in this thread so far.