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Old 11-19-2008, 05:26 PM   #1
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Another dimmer question {also wik pic}


My sister asked me to replace a rotary dimmer switch that had gone bad. It controls her dining room light. When I showed up, someone else (a friend of hers) had already removed the old one (and apparently wasn't sure what to do so he just left it.) The two black wires were connected to each other, and the two white ones were also connected to each other. I don't know if they were originally that way or if the guy who removed the old one did that himself just to keep them from hanging.

Anyway, putting a multimeter on it shows that when I touch the upper black one and the lower white one I get 120V. Any other combination gives me zero. The new switch has two black wires and one green (ground, I assume.)
There is no bare copper wire so I assume the red one is ground.


So how do I hook up the new rotary switch?

Thanks,
Steve S.
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Old 11-19-2008, 08:08 PM   #2
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Another dimmer question {also wik pic}


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Originally Posted by Steve S View Post
My sister asked me to replace a rotary dimmer switch that had gone bad. It controls her dining room light. When I showed up, someone else (a friend of hers) had already removed the old one (and apparently wasn't sure what to do so he just left it.) The two black wires were connected to each other, and the two white ones were also connected to each other. I don't know if they were originally that way or if the guy who removed the old one did that himself just to keep them from hanging.

Anyway, putting a multimeter on it shows that when I touch the upper black one and the lower white one I get 120V. Any other combination gives me zero. The new switch has two black wires and one green (ground, I assume.)
There is no bare copper wire so I assume the red one is ground.


So how do I hook up the new rotary switch?

Thanks,
Steve S.

Hey Steve I have two ideas here one thing to remember is that green or bare is always ground. Now if you have a metal box look in the back of the box you might see a bare wire around the screw in the back of the box. If not than it is possible that you have a ungrounded romex. Now my thoughts are these.

1) If the light the dimmer controls is also controlled by another switch you need a three way dimmer. Splice the white wires together put a cap on it and bury it in the back of the box. Next the 3 way dimmer you have will have two black wires, one red wire, and one gree wire. Remember green is ground. If you dont have a ground than just put a cap on the green wire. On the dimmer you will see a red and a black wire very close to eachother and you will see another black wire further away from the two. The wire that is further way from the other two will attach to the black wire that is by itself in the box. The red will attach to the red and the black will attach to the black that is coming out of the same cable as the red in the box. Remember only do this if the light is controlled by two locations.

2) Sometimes what electricians will do is run a three wire up to the light in cause they ever want to install a fan. By three wire i mean a red, white, black, and of course green. Now if that is the case what you should try to do is splice the white wires together cap them off and bury them in the box. Now coming from one of the cables you will have a black and a red those would be coming from the light most likely. The black by itself is power. So to find out what wire controls the light touch the power wire to the other black wire if nothing happens touch it to the red wire. One of those wires should turn on the light. Cap off the wire that doesn't control the light and you will need to get a single pole dimmer. On a single pole dimmer you will have two blacks and a green. Remember if you dont have a ground just cap off the green. And you will have two blacks left. Attach the wires of the dimmer to the wires in the box and your all set!

From what it looks like in the picture you have a three way dimmer but double check and good luck

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Old 11-21-2008, 12:34 AM   #3
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Another dimmer question {also wik pic}


Thanks for the response. I couldn't find any ground wire in the box so I just taped off the end of the green wire. I should point out that the house was built circa 1960.

Steve S.
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Old 11-21-2008, 02:16 AM   #4
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Another dimmer question {also wik pic}


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Thanks for the response. I couldn't find any ground wire in the box so I just taped off the end of the green wire. I should point out that the house was built circa 1960.

Steve S.
The ground wire must be bonded to that box, and connected to the switch if it has a ground terminal. This means you want to wrap the ground wire around a screw in the back of this metal box at a minium.

Jamie
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Old 11-21-2008, 12:21 PM   #5
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Another dimmer question {also wik pic}


You most likely have armored cable with a bonding strip, connect the ground to the box using a grounding clip or screw is the best...


How did you wire the dimmer? was it black to black, with one dimmer black. White to white. Other dimmer black to red?

Just curious.
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Old 11-21-2008, 05:34 PM   #6
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Another dimmer question {also wik pic}


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Originally Posted by rgsgww View Post
You most likely have armored cable with a bonding strip, connect the ground to the box using a grounding clip or screw is the best...


How did you wire the dimmer? was it black to black, with one dimmer black. White to white. Other dimmer black to red?

Just curious.

If you look at the picture he has two wire cloth romex not armored cable
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Old 11-21-2008, 06:17 PM   #7
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Another dimmer question {also wik pic}


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If you look at the picture he has two wire cloth romex not armored cable

Ohh, I saw only the paper...Well then he must use plastic screws with a plastic plate to meet code and be safe.
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Old 11-21-2008, 06:59 PM   #8
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Another dimmer question {also wik pic}


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Ohh, I saw only the paper...Well then he must use plastic screws with a plastic plate to meet code and be safe.
Hun?

I've never heard of using plastic screws, are you serious? What part of the code discusses this?
Thanks

Jamie
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Old 11-21-2008, 07:15 PM   #9
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Another dimmer question {also wik pic}


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Hun?

I've never heard of using plastic screws, are you serious? What part of the code discusses this?
Thanks

Jamie

I read the code wrong, actually you must use a non-conducting, non combustible faceplate, or just use a gfi. 404.9 (b) (exception)
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Old 11-21-2008, 07:27 PM   #10
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Another dimmer question {also wik pic}


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I read the code wrong, actually you must use a non-conducting, non combustible faceplate, or just use a gfi. 404.9 (b) (exception)
That is only if it is accessible from grade or a conductive floor/surfaces.
You CAN replace an ungrounded switch with another ungrounded switch.
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Old 11-22-2008, 11:31 AM   #11
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Another dimmer question {also wik pic}


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Ohh, I saw only the paper...Well then he must use plastic screws with a plastic plate to meet code and be safe.

Plastic screws? Huh?

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