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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.

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"code" meaning the NEC? –  Steven Nov 16 '12 at 20:53
    
Yes the NEC Code. –  Robert Nov 16 '12 at 22:18
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2 Answers

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 ( ;-) there are legitimate reasons to over size conductors) Table 210-21(b)(3) [outdated version used, sorry] thus indicates receptacles on such circuit cannot be rated over 15 amp.

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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 '12 at 23:26
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Use a 15A socket due to the 15A breaker. It's not waste to oversize copper for long runs. –  Fiasco Labs Nov 17 '12 at 2:36
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Back when copper was cheaper, oversizing romex from 14 to 12 was common in upscale jobs. –  shirlock homes Nov 17 '12 at 10:13
    
+1 @ bcworkz. The device must be no larger than the circuit interupt device. –  shirlock homes Nov 17 '12 at 10:15
    
Re: oversized conductors. Fair points. I was just being silly, no offense intended towards legitimate oversizing. –  bcworkz Nov 17 '12 at 23:43
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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.

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+1 for quoting the relevant passages. –  ArgentoSapiens Nov 19 '12 at 13:57
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