NEC Changes For #14 Ampacity

FionaZuppa

Senior Member
Location
AZ
update:
so, after the last semi-failed experiment i had to take a break from testing, working on a few other things that is consuming my time. i am planning to do more testing, and at the same time i am re-thinking data acquisition, looking at USB data logger for grabbing temps, like NI USB-TC01 or something from DATAQ.
 

mbrooke

Senior Member
Location
United States
update:
so, after the last semi-failed experiment i had to take a break from testing, working on a few other things that is consuming my time. i am planning to do more testing, and at the same time i am re-thinking data acquisition, looking at USB data logger for grabbing temps, like NI USB-TC01 or something from DATAQ.
Awesome! :D Go you, sounds like a plan :thumbsup:
 

Greg1707

Senior Member
Location
Alexandria, VA
Occupation
Business owner Electrical contractor
summary of this thread

summary of this thread

Can some one please summarize the content of this thread so that I do not have to read over six hundred posts?
Thank you in advance.
 

FionaZuppa

Senior Member
Location
AZ
1. If you hook 14AWG romex to up electricity it gets hot.
2. It can handle more current than the NEC tables in 310.15 allow for.
and,
3. CEC changed #14 to 20A
4. why does nec have blatant 15A max OCD for all #14
5. is #14 romex ok on 20A OCD for specific types of wiring
6. how did nec get to where it is now on ampacity, supporting evidence, etc

there is data out there from various testing.
 

mivey

Senior Member
Because it works.

Can we move on now?
I don't think this is going to change anything, but some of the thoughts about the physical reactions are interesting. The human interplay can be entertaining as well if you read back far enough (from a sitting-on-the-bench-at-the-mall-watching-people perspective anyway).
 

mbrooke

Senior Member
Location
United States
Then I'm thinking some of your observations are similar to mine. :)
What am I missing :blink::?

Yes me and Fiona are the top commenters in this thread, but that is because I am guiding Fiona in conducting his experiments regarding CCC. I cant think of a better way to find the actual ampacity of wire then real world tests. Also, if his tests are revealing in any way, such data can be used in a code proposal. Sure Mr. Zappa is not a certified NRTL, however his findings can spark discussion none the less. As well as a learning tutorial for future engineers.
 

mivey

Senior Member
What am I missing :blink::?
That different people view threads from different perspectives. Ten people will probably notice much more than ten different things about a thread. Some things they notice will be the same. The longer the thread, the more to note. Just different perspectives, not much more than that.

I have found some interesting things and some entertaining things so I keep reading even though it is a long thread. Don't mind me. Carry on.
 

mbrooke

Senior Member
Location
United States
That different people view threads from different perspectives. Ten people will probably notice much more than ten different things about a thread. Some things they notice will be the same. The longer the thread, the more to note. Just different perspectives, not much more than that.

I have found some interesting things and some entertaining things so I keep reading even though it is a long thread. Don't mind me. Carry on.
Thanks for the clarification. :) I know, Im commenting on everything in this thread :lol::ashamed1:

However lots of perspectives thus far, all valid concerns/observations/perspectives. Half the stuff I would not even have thought of.

Im really curious what Mr. Zappa obtains for conductor temps in common situations such as a fiberglass sandwich or fiberglass insulated wood stud sandwich.


After crunching numbers and sifting through data best I can (though I am very humble), I have come up with a theory (which I will use as base reference) that the 90*C column is based on an operating temperature rise of 44 to 55*F at full load, 3 conductors at 86*F. If true this alone would justify restricting NM to the 60*C column as adding thermal insulation would significantly increase temperature rise when measured after thermal normalization (equilibrium) resulting in actual temperatures well over 140*F.

However, there is one fact which challenges my theory. If we restrict NM for these reasons, then why do we de-rate starting from the 90*C column? And, alike, also challenging 240.4 (D); surely a conduit with 9 CCC #14 conductors each running at 15 amps will run hotter then only 3 conductors carrying 15 amps under identical conditions.

Mr. Zappa's testing will give actual numbers to prove or disprove our theories as well as providing a solid reference to work with.
 

FionaZuppa

Senior Member
Location
AZ
derate #14 or #12 for what reasons? regardless of wire type (NM, etc) these wire sizes have a blatant ocd restriction. why does NEC even have verbiage about "NM" to 60C column if #14 ocd cant be bigger than 15A and #12 ocd cant be bigger than 20A?

almost all residential wiring to motors use NM most/all of the way, so why does NEC allow 15<ocd for motors? sure, the running amps should be less than 15 on #14, but nonetheless the ocd (per NEC verbiage) defines the bc ampacity, not the wire. from my view, the NEC as-is has some conflicting exceptions.
 

mbrooke

Senior Member
Location
United States
derate #14 or #12 for what reasons?

More then 3 conductors in a raceway as seen in table 310.15 (B)(3)(a) (see pic).



regardless of wire type (NM, etc) these wire sizes have a blatant ocd restriction. why does NEC even have verbiage about "NM" to 60C column if #14 ocd cant be bigger than 15A and #12 ocd cant be bigger than 20A?
I do agree with you, and you have evidence through testing backing this up regarding two wire NM in open air can tolerate a LOT more then 20amps.

The 60*C verbiage is in place because larger NM sizes are not bound to 240.4(D), and 240.4D exists because THHN in conduit is not restricted to 60*C.


almost all residential wiring to motors use NM most/all of the way, so why does NEC allow 15<ocd for motors? sure, the running amps should be less than 15 on #14, but nonetheless the ocd (per NEC verbiage) defines the bc ampacity, not the wire. from my view, the NEC as-is has some conflicting exceptions.

The wire will never see continuous current past the listed minimum circuit ampacity which, is nothing more then the motor max current times a 125% safety factor. The key word is continuous, because the wire never sees more then the MCA except under short circuit condition, which will then pull hundreds if not thousands of amps. Hundreds of amps will trip a breaker at most within a few seconds. Thus, the breaker is only intended to provide short circuit and ground fault protection, not overload protection. Overloads via excessive motor loading (such as dirty condenser, plugged capillary or bad bearings) will be cleared via motor overloads integral to the unit which basically do the job of a 15 amp breaker.
 

FionaZuppa

Senior Member
Location
AZ
ah, my bad on the derating rant.

as for motors, if the ocd is 20A on #14 then the bc is a 20A bc, there could be a small value "short" that takes the wire to say 19A w/o ocd tripping ???
 
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