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One of my guest bedrooms in 1977 home has no ceiling fixture/wiring. I want to add wiring for a ceiling fan.

I know I have 20amp circuit breakers and I know I will have to splice to an existing wire in the attic in a junction box.

In the attic, however, all the existing wires are either round brown/black or flat white.

I'm pretty sure the white wire is 14/2 romex. What would the round brown wires be? (Inside the jacket are just a black, white and ground wire)

From my research, I should only splice like wires together, but its my understanding that with 20 amp circuits, I should be using the yellow 12/2 romex wire. But I am afraid to splice it to the white or black cables in the attic if they aren't the same gauge.

Is there a way I can verify the gauge rating of the cables and just use the same gauge wire to the new fan? Or should I be more concerned that I am potentially using 14/2 wire on a 20 amp circuit?

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    A picture will go a long way toward helping people ID your existing wiring (seriously, these people can tell a lot from a decent pic!). Bear in mind, though, that color-coded NM-B jackets only showed up around 2001. Heck, my entire garage is wired in white jacketed NM-B, and I know some is #12 and some is #14, and I wired it in 1995. The color of the jacket is really only a helpful tip, not an iron-clad guarantee - especially if it's older wiring.
    – FreeMan
    Sep 20 at 16:25
  • Most cables should have labels/marks on the outside saying the gauge, look where it is easy to see cables(at panel usually easy). 20 amp circuits will have 12 gauge if done to code. Size gauges are available but need power off so you can place end of wire into gauge.
    – crip659
    Sep 20 at 16:38
  • If that brown is really yellow then it is 12AWG Sep 20 at 16:47
  • Just going to throw this out there - if you can see the actual wire conductor, 12g is about the thickness of a nickel, and 14g is about the thickness of a dime. Can make it easier to ID the wire if you don't have anything else to compare the size.
    – JPhi1618
    Sep 20 at 16:47
  • I really thought I took a picture of the wire while I was up in the attic but couldn't find any on my phone when I created this post. I might be able to get a picture of the brown cable at another fan that I installed earlier. So if it turns out to be a 14 gauge wire should I splice another 14 gauge wire for my new fan, or splice a 12 gauge to it? (considering im on a 20 amp breaker)
    – Josue
    Sep 20 at 18:24
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To reliably determine the gauge of the copper wire inside your brown unmarked jacketed cable from 1977, use a wire gauge that comes with wire strippers like this one:

enter image description here

You'll need access to the copper core, which means you need to get into a junction box or other outlet box that the cable leads to, and disconnect the black or white wire at a nut or screw.

Then first close the stripper and then feed the copper wire core (without insulation) through the stripping hole. If it clearly doesn't fit the wire is larger, if it rubs through it has the gauge of the hole, and if there's wiggle room... well it's under gauge.

It's good to straighten the wire if it's bent or crooked from the screw or cap; it's even better to cut off the exposed part of and re-strip a fresh end since bending and straightening can weaken the core.

If you are on a 20amp breaker all wiring must be AWG12 (or bigger gauge). The breaker protects the wire from overheating and starting a fire. If part of the wiring is AWG14 you have to downsize the breaker to 15amp.

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  • Doh, thanks that is a great idea to identify it. So if it turns out to be a 14 gauge wire should I splice another 14 gauge wire for my new fan, or splice a 12 gauge to it? (considering im on a 20 amp breaker)
    – Josue
    Sep 20 at 18:28
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    If you are on a 20amp breaker all wiring must be AWG12 (or better). The breaker protects the wire from overheating and starting a fire. Remember to upvote answers you liked.
    – P2000
    Sep 20 at 18:30
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    @Josue, if there is any 14ga wire in the circuit, you need to replace it with 12ga, or drop the breaker down to 15A. You can mix the gauge of wire for extensions or repairs (best practice would be to use the same gauge to avoid confusion), but the breaker has to be sized for the lowest size of wire.
    – JPhi1618
    Sep 20 at 18:31
  • Although 2 14ga can technically carry the current of 1 12ga, this is an extremely bad fire hazard. If one of those wires disconnect, you just burned your house down.
    – Nelson
    Sep 21 at 3:24
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To answer one of your questions, using the "same size" wire as you already find on a circuit is not the rule. It's a clue.

  • There may be #12 wire on a 15A circuit simply because the installer had available a piece of #12 the right length for the job. Nothing wrong with that, but you don't have to match it, you can use #14 wire.
  • OTOH there may be #14 wire on a 20A circuit. That's wrong, you ought to fix it by changing to a 15A breaker and assessing what loads you have on it. If you don't fix it, you certainly should not extend the circuit with more #14 wire.

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