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I am trying to add an unswitched receptacle in my basement by tapping into a wall switch. There are 2 other switches that control the basement lights also. The wires into this particular switch are black white and red + ground. What wires do I run to the receptacle?

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  • Can you clarify how many cables/wires are available in this switch box? My answer below assumes there is one cable, with red/white/black (plus ground). But if you have multiple conductors of any wire in this box that might change the answer. Post details (and ideally picture) please. – Shimon Rura Oct 26 '17 at 20:22
  • Can you post photos of the inside of the box in question? – ThreePhaseEel Oct 26 '17 at 22:00
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How is this switch wired? Is it a 3-way switch or a simple on/off switch? (It's a 3-way switch if it is one of two switches that can toggle your lights on/off. It's a simple on/off switch if there are no other switches that control the same lights.)

If it's a 3-way switch, then its two positions toggle a "common" conductor among two "traveler" conductors. Usually white is wired to common (one side of the switch) and black and red will be different travelers.

In that 3-way configuration, the box containing the circuit does not have a neutral available. The neutral will be available at the light or at the other switch box. This means you cannot run a new outlet from the wires in this box - you need a neutral wire.

If it's a simple on/off switch with 3 black/white/red wires, then it's possible that you have a neutral (which will not be connected to the switch because all the switch needs to do is connect/disconnect a hot conductor). Typically that will mean your white neutral wire is unused (should be capped with a wire nut) and the switch will connect black to red when turned on. If that's the case, then you can run a new outlet by connecting to the white neutral wire and the black (always hot, not switched) wire. You could also run another switched fixture from this outlet using white and red (switched hot) wires.

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You can't use ground for anything, it is not allowed to carry current at all, and will create a very dangerous situation if it does. So not counting grounds, what you need there is two wires:

  • Always-hot
  • Neutral

It will vary a lot depending on how the 3-way switch loop was wired. The junction box might contain

  • 2 messengers and switched-hot or
  • 2 messengers, switched-hot and always-hot or
  • always-hot, neutral, and 2 messengers

Hope you're lucky. If the supply to the lighting circuit comes into that box, you're all set -- however if that were the case, you probably would not be asking here.

Colors will be useless, as they'll be random and confusing, like this. If you really want to spend the time to understand the circuit, do as I advise here, after buying some black, red and purple tape. (or yellow, it comes in 5-packs with other useful colors).

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  • I was going to say that there aren't enough wires for it to have 2 messengers and switched hot, but actually the question is ambiguous as to whether there are just 3 conductors, or whether there might be more than 3 conductors but in only 3 distinct colors. I'll ask for clarification. – Shimon Rura Oct 26 '17 at 20:20

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