3 Romex cables into box for two switches?

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Old 09-13-14, 11:15 AM
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3 Romex cables into box for two switches?

Hey All, new member and first post.

I am changing out the old dimmer switches on a two-switch box and made the dumb mistake of not noting how the old wiring was connecting those switches.

There are three Romex cables going into this box for two switches. I am not sure how to wire these switches. I have wired the switch on the left with one set of Romex and wired the other with the second set...leaving a set of unused Romex.

What happens is the switch on the left works great with the one of the right not. I have switched out the Romex for the right switch and it does not make a difference. My limited experience leads me to believe that the circuit is in need of all three to be used somehow to complete the circuit and I'm sure that it's a simple pigtail but not sure how to go about this and obviously don't want to play guessing games. One of the Romex is labeled 'A.'

I have attached a photo which hopefully will shed some light on my predicament. Any insight for this novice is very much appreciated.

Madtown Brian

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Old 09-13-14, 11:26 AM
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Welcome to the forums! How were they wired originally? Oops. You will need to determine which of these cables carries power using an analog meter. Once you determine that, we may be able to help you get the dimmers installed. If they are electronic dimmers, DO NOT connect them to any wires until you determine the correct positioning. You can blow out the circuitry if improperly connected. One cable appears to have a single black wire capped. Is that correct? Shadows in the photo make it difficult to see.
 
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Old 09-13-14, 11:29 AM
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Welcome to the forums.

You have three cables there. With a voltage tester or a voltmeter you need to determine which cables have power on them.

If the left hand switch is working..... don't change the wiring.

If the right hand switch is the only one not working I would splice the two whites together and cap with a wire nut. Now connect both of the blacks to the right switch. Try with a switch before installing the dimmer.
 
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Old 09-13-14, 11:42 AM
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Wiring

Basically the left switch is working. (the photo is of the new switches which are simple rockers, not dimmers.)

What's left are two Romex where one is completely capped (I know the ground doesn't need it, but hey, did it anyway).

The remaining Romex is connected to the switch on the right and does not work.

I have also tried swapping out these unused Romex with the same result. So perhaps I will try PJMax's advice about splicing white's together and then hooking up the two blacks to the switch. I just thought that the switch would need one black and one white.

Would I pigtail the grounds then to wire the ground to the right switch?
 
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Old 09-13-14, 11:46 AM
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I don't want to complicate matters, but.... Are you sure switch on left (above picture) works?
It turns light on and off as wired in picture?
Post back.
 
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Old 09-13-14, 11:49 AM
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Brian, I think the one on the left is on a switch loop, and may very well work as indicated. The switch on the right may require energy, thus the third cable. We'll see in a few minutes
 
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Old 09-13-14, 11:51 AM
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I think you're right and PJ's right Chandler. Normally you would test this, but it's obvious.
 
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Old 09-13-14, 11:53 AM
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Yes, the switch on the left currently works.

So to summarize, I will splice two whites together and connect switch with remaining black wires.

I assume I should splice and pigtail the ground and connect that as well?
 
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Old 09-13-14, 12:00 PM
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Yes, we don't mention grounds, but they are always spliced and connected through continuously.
 
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Old 09-13-14, 12:49 PM
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Sorry for the delay, I had to wait for the smoke to clear and the fire department to leave.

Just kidding – all is now working! Thanks for the great guidance.

Somewhere in my self-learning I thought I always needed a white and a black to a source and never considered using two black wires.

Much appreciated.

- Brian
 
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Old 09-13-14, 12:56 PM
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Basically all you are doing with a switch is breaking the current in the black wire, since the neutrals are tied together. Glad you got it fixed !
 
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