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[Princi]

First let me state that I've been using the X10 products for years.  I travel a lot and like having computer control of the lights, TV, etc. to give the house a lived in look.  Having returned from a 4 year international assignment, we decided to totally remodel the house, which included new lights.

Rather than turning off the circuit breaker, I typically turn off the switch and then test for voltage using a Greenlee GT-11 (Yes, I test it on a live circuit first to ensure the batteries haven't died).  So changing an outside light, I put up the 10' step-ladder and turned off the X-10 wall switched that controlled it.  I tested for voltage and there was none.  Next I removed the old light and left the wires hanging.  The new light required a slightly different mounting configuration.  While working on it (in a metal box), I suddenly received an electrical shock and nearly fell off the ladder. 

Wondering where that came from, I then tested again and found the black lead had voltage.  OK, turn off the breaker.

Yesterday while changing the kitchen light (in a 14' ceiling), I was a bit more cautious because it too is controlled by an X-10 wall switch, and I was back on that 10' ladder again.  Light was off - no voltage.  I then removed all 6 light bulbs, and wow there was voltage again.  Screw in a bulb, no voltage - unscrew the bulb, voltage.

So without a load, there is voltage being passed through the X-10 switch.  I doubt that there is enough current to kill you, but the voltage is enough to shock you and you could lose your balance if on a ladder.

There may have been a warning in the box with the original switch, but the switch has been there for years so why would I have kept the warning.

Moral of the story:  you can be bit by technology.  Best bet is to always turn off the breaker, and hope you can turn it on again (I've had breakers go bad after shutting them off).

[Brian H]

If it is a two wire dimmer type. It steals the power through the load. So no load and a high impedance meter or neon tester. Will show close to line voltage. That is why they have the little slide switch near the button. To break the circuit.

You don't by chance have FPE Stab-Loc breaker do you?
There are many internet sites that give details of how they fail and other problems. 
I gave my breaker box a real good look at as it is a Federal NoArc with Stab-Loc breakers.
At least mine is not the 'Rule Of Six' version and has a copper buss with no standoffs.

[JeffVolp]

Two-wire X10 switches must receive their power through the load.  Even when off, there will be a slight current flow to power the switch's circuitry.  The X10 wall switches I am familiar with all have a safety lever to entirely open the current flow when changing a bulb.  That is usually a little slide lever at the bottom of the switch.  On the Leviton switches, it is a little clear plastic lever that pulls out.

Relay switches may not have that lever because the circuit is open when the relay is off.

Oh, and I have also had a circuit breaker (Square D) fail to open circuit when switched off.  That gave me quite a surprise when doing some electrical work.

Jeff

[dave w]

There may have been a warning in the box with the original switch, but the switch has been there for years so why would I have kept the warning.

Moral of the story:  you can be bit by technology.  Best bet is to always turn off the breaker, and hope you can turn it on again (I've had breakers go bad after shutting them off).

No warning on the box, but is the first step in the instructions.

Yup, I have had breakers go bad when I shut them off, but it is a chance you have to take. If you have a "standard" switch installed on an "end run" , you can turn off the switch and still have the socket be "live" to ground, it won't be live to neutral since the neutral is now open circuited by the switch. (I found this out when grabbing wires while on an aluminum ladder on wet concrete, I'm not sure which hurt the most; the shock, or the fall from the fourth step, but it hurt). And as others have pointed out, the X10 switch will always leak voltage/current until the little slide under the button is slid to the outside. Glad to hear you are able to tell us the story.

[Princi]

I knew the little lever on the bottom would prevent the light from coming on, but I didn't realize that it will cut off the power to the load.  OK, that will save me from to go find and trip the breaker.  I still have several more fixtures to change out.  Thanks guys.

[crowntown]

I don't quite understand why you'd take any risk just to save a bit of time.  I'll gladly lose a minute of my time to do things the right way and turn off the breaker.

[Brian H]

The cut off switch is a UL requirement for dimmers and that is what it was designed for. Kill the power to the load.
Breaker is an extra percaution that one may want to use.

[Uncle Tom]

 (I found this out when grabbing wires while on an aluminum ladder on wet concrete, I'm not sure which hurt the most; the shock, or the fall from the fourth step, but it hurt).

Sorry if it offends, but... Anyone who uses a conductive ladder when working on electric circuits, under any circumstances, is a potential candidate for the "Darwin Award".

[dave w]

(I found this out when grabbing wires while on an aluminum ladder on wet concrete, I'm not sure which hurt the most; the shock, or the fall from the fourth step, but it hurt).

Sorry if it offends, but... Anyone who uses a conductive ladder when working on electric circuits, under any circumstances, is a potential candidate for the "Darwin Award".

Nah, it don't offend. I can rationalize it. Pick the most correct answer.

1. I thought the power was off.
2. I thought rubber feet on ladder would insulate.
3. I thought I was young and invincible.
4. I could not afford a fiberglass ladder.
5. I told the story to convince the OP that turning off the wall switch is not a guarantee that the fixture is dead.
 

[bendixgomez]

Turning off the wall switch is not a guarantee that the fixture is dead. I guess that could be a safety precaution...

[steven r]

A neon tester should be in every tool box of anyone that plans to do any wiring.
They're cheap and will definitively let you know the power is off. Use it to check every exposed connector in your switch box.

I had a shocking surprise once* after turning off the power to my light at the breaker. Turns out one of the other switches in the multigang box was on another circuit.


*Key word here is once.

[HA Dave]

A neon tester should be in every tool box of anyone that plans to do any wiring.

Those are nice little devices!!!

I helped an electrician when I was a young man. Working in the trades never worked out for me.... but I learned a lot. Mostly... how to fish wire... and a little about troubleshooting. But more to the point... we often worked with live power. And the point is: it didn't make any difference if the wires were hot... or not. We handled everything as if it was hot. Just like you should always handle a gun as if it loaded.