enter image description hereenter image description hereI'm installing a new dedicated 20 amp circuit for an existing bathroom (new fixture). NEC recommends 12 AWG wiring. But ALL the wires (regardless of amperage) in the main service panel are a much heavier gauge (I'd say in the neighborhood of 6 or 8 AWG). In comparison, my 12 AWG looks pretty small when wired to the 20 amp breaker. Should I be using a different (lower) gauge in the main service panel (to match the others) and then change to 12 AWG in a junction box?

The two photos (one, a closeup) shows the difference.

  • Post a picture of this service panel (open.) – Ecnerwal Jun 25 '17 at 13:08
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    What size is written on the sheath of those other cables? Reason I ask is that insulation diameter has nothing to do with wire diameter. Also do those cables do anything weird? E.g. If 11 of them all ran up the same raceway together for more than 24", they would have to bump up 4 sizes. – Harper Jun 25 '17 at 15:29
  • I hadn't considered that; thanks! I think you're dead on about the run. My circuit is hardly even 30', so I think I'm ok from one of the other responses. Thanks so much! – Dave De Seguirant Jun 25 '17 at 17:35

Code requires a minimum 12 AWG wire for a 20-amp breaker. You are fine with #12 wire. I have wired quite a few homes where the owners wanted 10-gauge wiring. 10-gauge can carry more current but is not needed unless it is a very long run: over 100 feet. Just to give an idea, #12 is rated for 40 amps with THHN but residential is limited to 20 amps for safety.

  • Great! Yeah; mine's a very short (~30'), so I should be ok. It just caused me to question myself when I saw those other diameters. I appreciate your answer! – Dave De Seguirant Jun 25 '17 at 17:37

What you are seeing is actually the insulation not the size of the conductor. To determine that you would have to read the writing on the wire itself or remove a wire and check it with a wire gauge.

That wire is definitely not #6 or #8 believe me. The insulation thickness has deceived you.

TW or THW type insulation from older wire was thicker than modern day THHN/THWN.

Your installation is just fine.

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