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As part of finishing my attic (insulation, drywall, etc.), I'm going to add receptacles and recessed ceiling fixtures. Currently, there are two 12/3 cables up there that are capped off, run by a previous electrician. These run down to the main panel to two 20A breakers labelled "Attic spare 1" and "Attic spare 2". If memory serves (I'm not home at the moment), each one is connected to a single-pole breaker, so I'm assuming the red wire is capped off in the box. I'll check this when I get home.

Regardless, my question is the following: for each 12/3 cable in the attic, should I extend it via a junction box using 12/2 cable? In other words, 12/3 going in (red wire capped off) and then 12/2 coming out? I have no need for split-wire receptacles or 3-way switches, so does it make more sense to just run 12/2 from the junction boxes? Or is there some reason that I should continue to use 12/3 throughout the room, to all the receptacles and fixtures? I don't have any 12/3 or 12/2 on hand so I want to know which I should plan to buy. Thanks.

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You can run 12-2 from the box to the other locations. If a double breaker one with a single handle or handle tied is installed you could use the red wire for a 2nd 120V circuit using the same ground and neutral. This is legal and called a multiwire branch circuit. This could provide up to 4 circuits if both "spares are 12-3. Capping the red is a fine way to do it if you only need the 2 circuits and want to run 12-2.

  • Thanks! I just checked and each cable is in fact connected to two single-pole breakers at the panel. Am I right in thinking that it's better to swap out those single pole breakers for double-pole, or at least to gang each pair of breakers together using an approved device? – johnnyb1970 Jun 30 '16 at 18:34
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    Yes they should have a handle tie or be a double pole to be legal. – Ed Beal Jun 30 '16 at 18:43

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