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Currently I have two wires running through the conduit: one hot (coming from box), and one hot switched (on/off according to light switch). I would like to convert it to an outlet switch combo (one outlet with a switch). So, I need to run one more wire, the neutral, to power the outlet.

The existing wires are old so I've removed them.

What wires should I use? THHN? What number (gauges), I'd say 12 is the suggested for outlets? Solid or stranded?

I mistakenly bought a 12/3 romex cable, which is too thick to run through the conduit. My understanding is that I can't strip the yellow plastic sheath that covers the wires, and just use the black, red and white wires, correct? Because I believe they don't have enough protection against damage. Correct?

What would be the right wire for this job?

The old wire had some textile/cotton on the outside, and it seems this is no longer used. What was this cable for, and why it seems no longer used?

Any help is appreciated!

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You want THHN wire. You will find stranded much easier to pull, but harder to terminate. Do not use backstabs with stranded!

Sizewise you must use #12 unless you know this is a 15A circuit. No option there. I just use #12 because the cost difference isn't so bad as it is with Romex.

You could've used the old wire to pull the new wire in. You can wrap the first 3-4 inches of the 3 wires together with tape - stagger them about 1" - and make the tape a bit lumpy so it's less likely to snag on things... at that point try pushing it through, if you fiddle enough you often get lucky. If that doesn't work, you can tie a string to a tissue and vacuum it through, and use the string to pull the wires through. Or get some proper "fishing tape".


Colorwise, use the correct colors since you can't remark wire in conduit.

The neutral must be white or gray, conventionally, white.

Hots can be black brown red orange yellow pink blue or violet. For simple 1-circuit pipe work, convention is black for always-hot and red for switched-hot.


Bat nailed it as to why you can't just shuck Romex. If the wire isn't marked THHN, it's not as tough as THHN. You can't use unmarked wire anyway.

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If the wires in the Romex have writing on them, stamped THHN, then you can strip the jacket and use them. However that's a lot of trouble and there's a chance you may nick the insulation in the process or otherwise damage the wires.

It would be easier and safer to buy THHN.

  • Thank you, would you suggest solid or stranded? – igorjrr Sep 5 '18 at 2:48
  • I'll say solid because it's simpler to connect securely to terminal screws. – batsplatsterson Sep 5 '18 at 3:24

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