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Discussion Starter · #1 ·
For reference:

"(B) Overcurrent Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) 
The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.
(2) 
The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) 
The next higher standard rating selected does not exceed 800 amperes."

To me, this sounds like you could use #14 for many kinds of 20A circuits in resi. Is this true? The ampacity for #14 is 25A @ 90 degrees C [310.15(B)16]. As such, my question is, why do we use #12 for 20A stuff that's not a multi receptacle circuit?
 

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To me, this sounds like you could use #14 for many kinds of 20A circuits in resi. Is this true? The ampacity for #14 is 25A @ 90 degrees C [310.15(B)16]. As such, my question is, why do we use #12 for 20A stuff that's not a multi receptacle circuit?
Not true, look at 240.4(D)
 

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Discussion Starter · #3 ·
OK, thanks. That seems to contradict this section in my textbook:



Ignore the highlighting.
 

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Keep in mind there are times when (D) does not apply, look at table 240.4(G) for a list of things it does not apply.
 

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Consider these points, paraphrased.

110.14(C) (1) Conductors smaller than 1awg or 100amps, ampacity must not exceed the 60deg column (15) unless the terminations are listed for 75 or 90 degrees. (Mostly academic at this point)

Remember you always derate at the wire rated temp and choose the lower of the options.

240.4(D)
14 awg shall be protected by no larger than 15 amp overcurrent device unless used in an application in table 240.4 (G) or allowed in either 240.4 (E) or (F) ooooooorrrrr 240.5 fixture wires.

334.80 The allowable ampacity of type nm wire shall not exceed the 60 degree column. Notice the peroid there are no qualifiers many say you don't have to do this if it does not come into contact with insulation. You would still start your derating from the 90degree column.
 
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