Well, if you are VERY careful and follow the rule to keep one hand behind your back at all times (to avoid grounding yourself by absently touching a ground while you handle live wires), you CAN work on such things with a live circuit. You can, but you'ld probably also be considered INSANE.

Turn off the breaker, then check the operation of that switch ... if it doesn't work, then there's no electricity in the circuit that could shock you. At that point, it's ok to pull out the old switch and install your new one.

MAKE SURE NOBODY TURNS THE BREAKER ON WHILE YOU ARE WORKING ON IT.

Skie, thank you for your reply.

The guy with one hand behind him sounds utterly insane. I can't even imagine. I'm undone by the prospect of mild static shocks. I'm certifiably shock-phobic.

Nobody is liable to turn on the breaker while I'm working on it. If it's off and the light no longer goes on at the switch, that's good, right? I feel like an idiot. :)

The one hand behind your back trick is a JOKE! You can still get a nasty shock if you create a path through your feet (YES, it CAN happen depending on conditions) or if your one hand brushes something grounded. Plus, working with only one hand is plain and simple STUPID.

For anyone not VERY experienced doing electrical work it is NOT an option to work live. Even for those of us who do it every day it is not a good idea, but most do it anyway for small things like replacing a switch. You just have to know what you are doing and be very careful.

For someone like you Linelle, I'd suggest getting someone to do it for you. Having respect for electricity and knowing what you are doing ahead of time is crucial. Being terrified of it (shock-phobic in your words) and having no experience is a recipe for disaster.

petey, a recipe for disaster even with the breaker off? The demo lady in the Lutron video makes it look so easy. I'll ask a friend if he'll help and I'll watch.

petey said it well...exactly what I was thinking. Besides, if you've never done this work, there are small things you should look out for that you might not know, like: being sure the loops at the wire ends are in the right direction, knowing how tight is tight on the terminal screws, making sure any existing wire nuts are still tight, taping over the side terminals if the dimmer is a tight fit, etc.

Okay, you guys have convinced me. I'll ask a DIY friend to change it for me and I'll observe from a safe distance. It irks me because I really thought this would be something I could do myself, but I'll defer to your experience and wisdom.

Does changing a light fixture have the same issues and dangers?

The day the guy installed the dimmer switch, he did not turn off the power at the breaker box. How does that happen?

Usually OK if you are careful not to touch the wrong stuff, but I've seen it pop a few breakers, burn the tips off screwdrivers and be generally unpleasant. A couple days ago the guy doing our house upgrades managed to explode the whole outlet. Dunno what he did - there was a flashbang and black smoke from the receptacle.

It's a time saver, except when it doesn't work.

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Swapping out light fixtures has the same dangers plus falling off the ladder.

Turn off the breaker to that switch and you are good to go. Check for power by turning on the light.

Locking the box might be needed if there are others in the house who bear you ill will or who are foolish enough to turn the breaker on without checking to see if you are finished.

The best way to learn is to have someone show you how - I learned as a child, from my safety conscious dad.

lazy, thanks for weighing in. I'm not concerned about someone turning the breaker on while working with wires. I live alone except for my cats. They may bear some malice toward me at times, but they're indoor-only and the breaker box is outside.

It's funny how I was dissatisfied with my existing dimmer switch and now I realize I can probably live with the one installed. :)

When I was about 4, I stuck a bobby pin into an outlet in my bathroom. I still have a vivid memory of it. I don't remember any pain, but there was a huge blue flash and suddenly I was knocked to the opposite side of the room. I had a tiny little mark in the palm of my hand. When I walked out to the kitchen to tell my parents about it, they went berserk.

More than once I've been (unpleasantly) surprised to discover that a box or light fixture is being fed from more than one circuit, so turning off one breaker may not be enough. This isn't limited to old or amateur work. I'm currently negotiating with the "master electrician" who wired my house about the string of outlets that require two breakers to be thrown to de-power them. These days I pretty routinely use my well-insulated screwdriver to ground any wires in a box prior to touching them.