# 240.4(B) Overcurrent Devices Rated 800 Amps or Less



## BBQ (Nov 16, 2010)

owl said:


> 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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## owl (Oct 31, 2012)

OK, thanks. That seems to contradict this section in my textbook:









Ignore the highlighting.


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## BBQ (Nov 16, 2010)

owl said:


> OK, thanks. That seems to contradict this section in my textbook:
> 
> View attachment 32031
> 
> ...


I would feel better about commenting on the book if you showed more of it. 

As far as the highlighting, you should see my code book, it is full off my highlighting.


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## BBQ (Nov 16, 2010)

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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## SteveBayshore (Apr 7, 2013)

Colored highlighting, what a great idea. I've been using a black magic marker to mark the stuff that I didn't agree with.


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## brian john (Mar 11, 2007)

SteveBayshore said:


> Colored highlighting, what a great idea. I've been using a black magic marker to mark the stuff that I didn't agree with.


:laughing::laughing::laughing::laughing::laughing:


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## BBQ (Nov 16, 2010)

SteveBayshore said:


> Colored highlighting, what a great idea. I've been using a black magic marker to mark the stuff that I didn't agree with.


All that is left showing is the title. :laughing:


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## Ultrafault (Dec 16, 2012)

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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