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My house was built in 1950 and several light switches do not have ground wires. I believe there is no ground wire since I cannot find a wire that's bare - they are all coated.

I want to install a Lutron Motion Sensor, but it requires to connect to a ground wire. This is for a hallway light that's also controlled by another switch at the opposite end. When I installed it without connecting the wires that are expected to be connected to ground, nothing happened. Meaning, the switch did not work. I assume it was because the documentation was correct, that ground needs to be connected.

The person at the hardware store said to only connect the ground wires to the screws that afix the light switch. Is this OK? Is this safe?

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Do you have armored cable (BX)? Is the box metal? How many and what color wires are in the switch box? –  bib Nov 29 '13 at 18:12

3 Answers 3

If there's no grounding means in the switch box, and no neutral wire present, then the switch you have simply won't work. Get a different switch that's designed to run its tiny control current through the attached light bulb filiment. Not an incandescent lamp, you say? Well, then, just rewire your house!

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Connecting the ground wires to the screws only works if the metal electrical box is itself grounded, which is unlikely the case if your cable does not have a bare wire. Also, I believe they started using a separate ground wire at the end of 1950s (at least in my part of the country). In any case, it is pretty easy to confirm (power down the switch at the breaker box, remove the switch and see if there are 3 or two wires going to the box. If there are three, you are in luck)

Even if there are two wires, I doubt it would be impossible to get the sensor working without the shared ground. I would double check the wiring and connections first and look at the circuit to makes sure that the ground is truly required (pictures would help)

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The literature proudly proclaims "no neutral required". Sounds like they are using ground as an ersatz neutral, which is technically illegal. I suppose the currents involved are minuscule is the rationale. If a neutral were available, I wonder if connecting the so called "ground" to neutral would allow it to work. I'm just speculating, not suggesting you try this. Not my fault if it burns up the circuitry in doing so. –  bcworkz Nov 28 '13 at 18:53
    
Ground (without a visible wire) is entirely possible if the in-wall cable is BX, which was dreadfully common for quite a while. Metallic conduit could also do that, but would not be nearly as common. –  Ecnerwal Dec 2 '13 at 17:12
    
While connecting the ground to the neutral will probably get the switch to work, I highly recommend you don't. By connecting the ground to the neutral, you will also most likely be connecting the your box and anything touching the box to neutral. If there is a fault, your box and anything touching it might become live. –  diceless Apr 30 at 3:50

I looked at the switch's instructions and it definitely says it needs a ground to function. It is possible that the switch box if metal is grounded by an armored cable connected to it, in which case you could install a jumper wire from a ground screw in the back of the switch box to your control. Take a look at your service panel and see if there're armored cables. Otherwise your house probably predates grounding.

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