You can do all kinds of things that makes sense but I would think, code is code.Yep, 20A breaker needs 12 gauge wire as per code.
But here is a theoretical question that makes sense in my mind. Let's say you have a few outlets on a 20A breaker and all are wired with 12 gauge wire. Assume you want to add a doorbell, and you tap power off of the last outlet in that 20A circuit. So you have to run wire from that last outlet to the 12 or 16 volt doorbell transformer. So beyond the outlet, the only possible draw of power will be the dinky little doorbell. So why wouldn't a gauge smaller than 12 be allowed between that last outlet and the doorbell transformer since it doesn't seem possible that anything beyond that last outlet will be drawing a lot of amps? I would think it would be okay to just use 14 guage between the outlet and the doorbell transformer. But I assume the answer is no. Just curious if anyone has any insight. Thanks.
And what would prevent someone from seeing that 14g in the future & connecting a heavier load? Then someone else realizes the 20a breaker shuts off power to that device & puts in an even heavier loadYou can do all kinds of things that makes sense but I would think, code is code.
That's not to exclude the possibility that in 20 years you are changing out that door bell for a laser sentry gun that draws 16 amps.
To be fair, a dead short would overheat any wire if power were not cut by the OCPD.Or what if you picked up a dead short at the transformer or someplace in the #14 wire? Nice fried wires.
Which devices? Most do not.. The OCPD should be sized for the lowest rated component of the circuit. If you used all #12 wire, but connected a receptacle inline with the branch wiring that was rated for max. 15A pass-through, the circuit would have to be protected by a 15A OCPD.Daniel Holzman said:The devices have their own protection.
Any 20A outlet you buy now should look like this:
Yes, they are.
Yes, but not all.. If it were rated for 15A pass-through, it should not be on a 20A breaker.
There is no need to buy a 20a outlet unless you have a 20a plugAny 20A outlet you buy now should look like this:
Notice has the neutral slot has the additional little slot coming off of it at 90 degrees. A 15A outlet won't have that perpendicular slot coming off the neutral slot. But the fail proof method to see the amperage of the outlet is to read the back and/or side; it will always say.
No, but the temp. rise above ambient will be (20/15)^2 times what it would be if the wire carried 15A.Yes, they are.
And just to be clear, while it is a violation to use 14ga wire on a 20A circuit in most cases, the 14ga wire will not burst into flames or all the insulation melt off if the current goes to 20A.
Not really. Remember, the listed ampacity for 14ga THHN (which is really what NM-B is) is 25A. It's the NEC that mandates, for most applications, the OCPD be limited to 15A.No, but the temp. rise above ambient will be (20/15)^2 times what it would be if the wire carried 15A.
I guess the insulation will just get brittle faster.
OK, so the temp rise at 25A is ~(25/15)^2 = 2.8x what the rise would be at 15A. I hope it's less than 90C, for a 30C ambient.Not really. Remember, the listed ampacity for 14ga THHN (which is really what NM-B is) is 25A. It's the NEC that mandates, for most applications, the OCPD be limited to 15A.