I have a hypothetical question:

If you have a 15 Amp breaker connected to a 20 Amp T type outlet with (20 Amp) 12 AWG wire, is it within code, below code, or above code, where code means the National Electrical Code.

This is due to a discussion I had with a colleague that insists it is not within code due to the 20 Amp T outlet. I view it as the outlet may be 20 Amp and any appliance you plug into it that draws more than the 15 Amp breaker will support will trip the breaker long before any overheating or electrical damage will occur.

Now I will agree that having a 15 Amp breaker and using 14 AWG wire with a 20 Amp T type outlet could potentially overheat the wiring, as the draw could be just over the 15 Amp breaker which they tend to trip around 16 Amps.

  • "code" meaning the NEC?
    – Steven
    Nov 16, 2012 at 20:53
  • Yes the NEC Code.
    – Robert
    Nov 16, 2012 at 22:18
  • 1
    I realize this post is ancient, but just a comment. A 15A breaker may never trip at 16A. Circuit breakers do NOT trip the instant current exceeds their rating, they trip on a curve, the more over the rating the faster the trip. I've seen perfectly good 20A breakers holding 25A for an hour or more. Dec 11, 2015 at 0:33
  • Many residential breakers are just cheap junk, not tripping for an hour at 25a is a good example though not too terrible. While there is some curve these aren't expensive delay breakers for industrial motor feeds. Also extended time right at the edge of tripping will cause long term wear and poor functioning.
    – Max Power
    Jul 4, 2022 at 8:33

3 Answers 3


The answer to this question can be found in article 210 of the National Electrical Code (NEC). Section 210.3 of this article, tells us that the circuit rating shall be determined by the overcurrent device rating.

NEC 2011
210.3 Rating. Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device. The rating for other than individual branch circuits shall be 15, 20, 30, 40, and 50 amperes. Where conductors of higher ampacity are used for any reason, the ampere rating or setting of the specified overcurrent device shall determine the circuit rating.

So if you have a 15A breaker, the circuit rating is 15 Amps. Section 210.21(B)(3), tells us to refer to table 210.21(B)(3) to determine the receptacle rating for circuits supplying two or more receptacles.

210.21(B)(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

Table 210.21(B)(3)

This tells us that if we have a 15A circuit breaker protecting a circuit with two or more receptacles, each receptacle on the circuit must be rated not over 15 amperes. It's also good to remember, that the NEC does not view a duplex receptacle as a single receptacle according to the definition of a receptacle.

Receptacle. A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke.

So if you're installing even a single duplex receptacle on the circuit, you'll need to follow 210.21(B)(3) and use a 15A receptacle.


Does not meet NEC because the circuit is rated 15 amp by breaker size [210-3], regardless how much copper you choose to waste on over sized conductors. ( ;-) there are legitimate reasons to over size conductors) Table 210-21(b)(3) [outdated version used, sorry] thus indicates receptacles on such circuit cannot be rated over 15 amp.

  • 1
    Wish you hadn't called it waste. Maybe it's a long run, and I plan to run a saw or pump.
    – Jay Bazuzi
    Nov 16, 2012 at 23:26
  • 1
    Use a 15A socket due to the 15A breaker. It's not waste to oversize copper for long runs. Nov 17, 2012 at 2:36
  • 1
    Back when copper was cheaper, oversizing romex from 14 to 12 was common in upscale jobs. Nov 17, 2012 at 10:13
  • +1 @ bcworkz. The device must be no larger than the circuit interupt device. Nov 17, 2012 at 10:15
  • Re: oversized conductors. Fair points. I was just being silly, no offense intended towards legitimate oversizing.
    – bcworkz
    Nov 17, 2012 at 23:43

The 20 amp receptacle poses no risk on a 15 amp run..... Capacity is determined by amperage at the breaker .... So if you draw 16 amps the fuse will trip either way.. Circuit protection is then not compromised......

  • Welcome to Stack Exchange, but this is incorrect, and violates code. Dec 11, 2015 at 1:35
  • The breaker should trip, but that leaves it as a single point of failure and assumes it works perfectly and is perfectly calibrated to trip at the correct current. It may cause excessive heating if right on the threshold of tripping, but not quite there. May 20, 2021 at 18:21
  • @GabrielStaples@GabrielStaples: The 15-vs-20 amp plug distinction seems less than ideal for plug-in devices whose power consumption would depend upon use--especially devices that are designed to convey power to other devices. If one sometimes needs an extension cord to power a 15A device from a 15A circuit, and sometimes needs to power a 20A device from a 20A circuit, having to use different cords for the two purposes seems a bit wasteful. Attempting to power a 20 amp device while the cord is plugged into a 15A breaker would likely trip the breaker, but that's no worse than...
    – supercat
    Jul 3, 2022 at 22:18
  • ...the common situation of trying to power two 12A devices from a 15A breaker, which the 15-vs-20-amp plug distinction does nothing to counter. If there had been a standard small-load plug in addition to the up-to-15A plug, then it would make sense to have light-duty extension leads with three small-load outputs, and normal-duty leads with one large and two small, but discourage attempts to power two or three 12A devices simultaneously with a light-duty cable.
    – supercat
    Jul 3, 2022 at 22:25

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