I replaced a single pole switch with a Lutron Maestro dimmer. However, the line remains "hot" when dimmer turned off. Have verified that the hot wire in box is wired to bottom lug of dimmer. I thought the dimmer was defective so I purchased another but having the same issue! I rewired the original single pole switch and verified that power turned off when flipping switch. I might add that I don't have the light fixture connected to the wires at the ceiling fixture yet, but don't think that this should matter since the original single pole shuts off power here.
Dimmers work differently
To start with, a dimmer is a smart device, and all smart devices need power themselves for their own internal functioning.
How do they get power? That's kind of a problem. A plain switch loop doesn't need neutral - it gets always-hot and delivers switched-hot. So many older switch loops are wired with no neutral. However, old style incandescent bulbs have a unique property: when they are not lit, their resistance is near zero. So many smart devices (and almost all older ones) power themselves by leaking power through the incandescent bulb. CFL and LED bulbs don't play well with this, unless they're designed to.
How do newer smart devices power themselves?
- Some newer still do it this way, because they're afraid of having a lot of returns from consumers who find out they don't have a neutral.
- Some simply require a neutral.
- Some misuse the ground wire as a neutral, and they don't blow GFCIs because they flow very little power. (How they make it through UL listing is a mystery to me.)
Dimmers which require or steal a neutral should not put any power on the line when "off", but you should not count on that for safety!
A dimmer without a neutral should, and must, energize the switched-hot at all times.
Some dimmers have a hard-switched "off" (and sometimes a hard-switched "on")... but it's past a stiff "detent" and people never push the switch hard enough to realize the detent is there.
Lutron 3-way switch failure AND SOLUTION
I have an LED lighting system on a 3-way with a dimmer. The LEDS would never fully turnoff. A real head scratcher.
My multimeter showed voltages all over the place. 90, 70, 20. Blew my mind.
Of course, I thought it was the dimmer. WRONG!
It was the Standard Lutron 3-way. I tore it apart to figure out how it could possibly fail so strange. My conclusion?
Lutron heavily greased the internal contacts. Open or closed, this grease bridges the contacts. Over time and use, small particles of metal from the contacts get entrained in this grease, causing it to become slightly conductive, and you get a high resistance short.
That means YOU CAN NEVER FULLY TURN THE SWITCH OFF, and it is constantly drawing power.