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Replacing a dimmer in an old house when there are only two black wires?


JoshD's Avatar
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04-14-18, 01:18 PM   #1  
Replacing a dimmer in an old house when there are only two black wires?

Hi all, I found a few other replacing a dimmer in an old house posts but none were quite the same situation as I'm dealing with.

I was trying to replace a dimmer in our new (but old) house (some new wiring, apparently some not). I knew what to look for wire color wise and where to connect it to the new dimmer which had four wires (red, green, black, white). The dimmer that was in there was functional but we wanted to install a smart home dimmer.

So I unscrewed everything, pulled the dimmer out and it only has two black wires coming out of one corner of the black box of the dimmer. Those were wired in to, from what I could tell, one of the two black wires in the wall using a wire nut.

Well, not having any of the wires I was expecting or requiring for my fancy new dimmer, I tried to put it back to rights and reinstall the old one and of course, it doesn't work anymore. I know its the wiring but I can't make heads nor tails of how to fix it.

Any help is appreciated, thanks!
JoshD

 
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04-14-18, 01:22 PM   #2  
Hi Josh, post some pics of the wires coming out of the box so we can see what is there.
Geo

 
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04-14-18, 01:25 PM   #3  
Will do, gonna have to kill the power and pull it back off after my second failed attempt...

 
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04-14-18, 01:31 PM   #4  
Did you break any splices open before?

 
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04-14-18, 01:51 PM   #5  

 
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04-14-18, 01:54 PM   #6  
Welcome to the forums.

If your old dimmer had two wires coming out of it... it would have had to have been connected to two wires in the box.

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04-14-18, 01:55 PM   #7  
To the best of my knowledge I didn't break any splices, but there was a bunch of electrical tape around the wire nut and from what I could tell both wires from the dimmer were going in to it prior to my messing around with the whole thing, so it's possible? I'm a raw greenhorn at this stuff.

 
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04-14-18, 02:22 PM   #8  
Ok..... there are two wires in that box. Although it's hard to see.... one is white and one is black. Turn the circuit off..... carefully remove the tape and wirenuts....connect your new dimmer to those two wires.

Just cap off the dimmer ground wire and leave in the box.

When wiring gets old.... the insulation gets hard and cracks off easily so handle the wires with care. A little bit of black tape around the insulation can help.


~ Pete ~

 
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04-14-18, 05:09 PM   #9  
Pete, the OP states the new dimmer has red, green, black, and white leads on it. It sounds like it's a "smart" dimmer that needs a hot and neutral present in the box in addition to the load. I question if it will work at all in this application, since this appears to be a switch loop, with no neutral present.

 
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04-14-18, 06:52 PM   #10  
Ahhh.... a smart dimmer. Thanks for the heads up. You are correct.... that is a switch loop with no neutral present which means that dimmer can't be used there.


~ Pete ~

 
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04-15-18, 08:49 AM   #11  
Thanks PJmax and Beachboy!

I figured as soon as I got in there I would be SOL given there wasn't a neutral so I'm going to try to reinstall the original dimmer. Sooooooo... which of the two wires out of the wire goes to which of the two wires in the box.

Thanks again for your help, this is such a great resource for a new and unhandy homeowner!

PS: Those wires sure look old and crazy. Any opinions on whether its time to update the wiring? Any safety concerns? Thanks again!

 
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04-15-18, 09:50 AM   #12  
Updating old wiring is always a good idea but it is not a walk in the park. The current wiring is fastened securely in the walls and is not easily removed. That means you abandon the old wiring to install new.

That looks like cloth covered BX cable. There is a lot of it still in use. Handle the wire carefully when working with it. Any sharp bends will crack the insulation off.

You can connect either dimmer wire to either wire in the box. The dimmer has no polarity.


~ Pete ~

 
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04-15-18, 10:47 AM   #13  
Do I need to connect both wires to one of the wires in the box, or do I connect one to each? Are both wires from the dimmer required?

 
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04-15-18, 11:45 AM   #14  
Do I need to connect both wires to one of the wires in the box, or do I connect one to each?
One to each.

Are both wires from the dimmer required?
How else could electric flow through the dimmer? The dimmer is basically joining power in to power out so electric can flow.


I can explain it to you, but I can't understand it for you.

 
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