I have a switch controlling two lights in hallway. I purchased the Lutron C-L DimmerScL-153PH-WH. I have 3 black wires and 1 copper wire coming out of wall. The old switch was not connected to the copper wire. The 3 black were connected to the switch with just an on/off toggle. How do I connect my new dimmer to the 3 black coming out of wall?

  • 1
    You probably should've marked things. The extra black probably feeds something downstream. You'll need to determine which black feeds the light circuit and which is the source hot.
    – isherwood
    Jan 10, 2017 at 15:38
  • 3
    Are there two switches that control the lights (3-way)?
    – Tester101
    Jan 10, 2017 at 15:59
  • Are any of the wires connected to the same terminal?
    – Jason
    Jan 10, 2017 at 16:28

1 Answer 1


Are there some white wires in the back of the box? If so, surely the blacks are:

  • One black (and partner neutral) which comes from power source. It will be hot all the time, even when separated from the others.

  • One black (and partner white) going to other things such as receptacles, light switches and the like, things intended to be always-hot.

  • One black (and its partner white) going to the lamp - the one controlled by the switch. If you wire power source to this, the lamp will be on all the time.

The normal connection is to a) hook up all grounds. b) attach the black/hot going to the lamp, to one of the switch terminals. c) tie the power-source and the "other stuff" hot to each other. d) Tie those two to the other terminal on the switch.

How to tie 2 wires to one terminal

  • I assumed that there were no neutrals in the box based on the wording of the question. Could have been mistaken, though.
    – isherwood
    Jan 10, 2017 at 22:02
  • 1
    I don't see how that could work, codewise. People often neglect the mush in the back of the box. Jan 10, 2017 at 22:51

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