NEC Changes For #14 Ampacity

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been in my oven at 300F (149C) for past 30min. the wire insulation still hard as can be. sure, it has to be softer, but hard to tell using my fingernail test.
the int paper and outer sheath show no signs of deformation, paper feels hot, outer sheath seems a tad more flexible.

will bake it to the 90min mark.

and just wanted to point out, temp alone doesnt mean too much. its energy that matters. a thin wire that is hot may not have enough energy to get a big piece of wood into that combustion zone, while a big wire that is giving up lots of heat energy at a lower temp than that thin wire could be bad for that piece of wood.
 
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ok, now we have something, at 53min @300F the outer sheath is soft and has begun to stick to the tinfoil it is laying on. no signs of burning though. int paper doesnt seem to have any issue at all, insulation on wire still seems rather stiff.

since i dont really know much about the "whys" in Romex (NM) engineering, wondering is the outer sheath is designed to show signs of a heat issue before the inner wires face a problem. perhaps turning blackish color before the internal wire insulation gets into that breakdown area? anyone know?
 
Grand Q's FZ

I'm compelled to ask how the nrtl's asses ? there should be some data we can place side by sided to your findings ...~RJ~
 
romex jockey said:
Grand Q's FZ

I'm compelled to ask how the nrtl's asses ? there should be some data we can place side by sided to your findings ...~RJ~
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dunno, what lab(s) has tested any of this before and have the osha cert? certainly my garage doesnt fit the bill, but the data i am providing is pretty darn accurate as far as i can tell. whatever discrepancies start to show up simply means we need a lab like Argonne (or university) to do formal testing.

as of now my i am leaning towards overly conservative on ampacity #'s, how much so is still TBD because i need to understand the rationale, wire temps do not seem to be an issue for the wire itself, however, wire temps and how they affect their surroundings might be more significant, etc. if you read back early in this thread there were two arguments for ampacity, 1) amp limits because the temps could damage the wire insulation, and 2) amp limits because the heat from the wire may cause damage to surroundings and cause a fire. with romex style the heat flux out of the cable is not that high when we look at unit density in that 15-25A range.
 
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more data for you. baked @300F for 90min.
the outer sheath got a tad like a rubber-band, it started to stick to the aluminum foil, and the color of wire insulation and sheath went from "white" to "light-almond", really the only way i can describe the color change. the internal paper didnt seem to be affected at all. i tried to slice off some of the wire insulation with a knife (butter knife w/ some not very sharp serrations), but it wasnt soft enough for the knife to grab into.

we would expect any properly installed wire that has good working ocpd to never allow enough amps to get the wire to 300F, and a odd fault that allowed persistent high enough amps to get the wire to 300F i do not think the wire would fail. i suspect if we went days in the oven we would see good discoloration but i dont think that would cause a failure, and arc'ing across the conductors due to compromise in insulation is a low probability, but only formal testing can confirm that.

 
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and sure, the insulation on the wire started to cool before i tried to knife it, but before i started the video i did try to peel it right when it came out of the oven, wasnt very soft. again, just some crude testing looking for obvious failures, none found, now getting ready to cook (with amps) the romex in a R10 rigid foam sandwich.
 
HRTL, Holt Recognized Testing Lab........:)

HRTL, Holt Recognized Testing Lab........:)

FionaZuppa said:
dunno, what lab(s) has tested any of this before and have the osha cert? certainly my garage doesnt fit the bill, but the data i am providing is pretty darn accurate as far as i can tell. whatever discrepancies start to show up simply means we need a lab like Argonne (or university) to do formal testing.

.
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Methinks i may have something for you hereFZ

hope it helps........

~RJ~
 
FionaZuppa said:
and sure, the insulation on the wire started to cool before i tried to knife it, but before i started the video i did try to peel it right when it came out of the oven, wasnt very soft. again, just some crude testing looking for obvious failures, none found, now getting ready to cook (with amps) the romex in a R10 rigid foam sandwich.
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So what's the dif between 'oven' and 'amps' doing the heating here FZ? All i can think of is 'external' / 'internal' .......?


~RJ~
 
romex jockey said:
So what's the dif between 'oven' and 'amps' doing the heating here FZ? All i can think of is 'external' / 'internal' .......?


~RJ~
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amps = not cooking it in my gas oven
does anyone have the actual UL 2556 doc? if not i can accept donations to buy it, only $716. :eek:
 
mbrooke said:
Unfortunately thats how they make $$$$, making standards, copyrighting them and then selling them.
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someone must have it, can share some of its verbiage?? we're not here to profit from it, using it for educational purposes, etc. but i dont think that is the UL # on the SIMpull wire i have. let me check, the romex i have is labeled E18679
 
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FionaZuppa said:
more data for you. baked @300F for 90min.
the outer sheath got a tad like a rubber-band, it started to stick to the aluminum foil, and the color of wire insulation and sheath went from "white" to "light-almond", really the only way i can describe the color change. the internal paper didnt seem to be affected at all. i tried to slice off some of the wire insulation with a knife (butter knife w/ some not very sharp serrations), but it wasnt soft enough for the knife to grab into.

we would expect any properly installed wire that has good working ocpd to never allow enough amps to get the wire to 300F, and a odd fault that allowed persistent high enough amps to get the wire to 300F i do not think the wire would fail. i suspect if we went days in the oven we would see good discoloration but i dont think that would cause a failure, and arc'ing across the conductors due to compromise in insulation is a low probability, but only formal testing can confirm that.

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The test was worth it, but it will take a lot longer for the wire to degrade. One major event indicating breakdown is "plasticizer migration" (worth researching).

There are a few free UL reports that did testing on NM wire as part of over driven staples, I will find them and post them.
 
FionaZuppa said:
someone must have it, can share some of its verbiage?? we're not here to profit from it, using it for educational purposes, etc. but i dont think that is the UL # on the SIMpull wire i have. let me check
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Hopefully one of the members reading this thread has it and can check in. Believe me, I am not to flattered about so much information being withheld when used for educational purposes.
 
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FionaZuppa said:
so, did the insulated wire open air tests. last one right at the top of the 60C column. as before, the probe just sat there until equilibrium was there for about ~10min or so.

note: in this pic the wire is about 1.25" above the table.
ambient air 60F
13.46A 70.7F (21.5C)
26.0A 84.7F (29.3C)
48.15A 137.3F (58.2C), basically feels warm to the touch.

that stated, ambient was different, but the relationship looks like 10F, so i might hypothesize normalization back to 70F ambient as:
13.46A 80.7F (27.05C)
26.0A 94.7F (34.44C)
48.15A 147.3F (64C), basically feels warm to the touch. 3.2x (2.57x more than 125% of rated ocpd) more than NEC's prescribed max amps with temp hitting ~60C. there is no way this temp has potential to start any fires, unless you bring me an example or scenario that you think might.

DSC02721.jpg
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For open air, this test proves 240.4(D) has no place in 310.15 B 17 (not 16).

The only thing that comes to mind is sunlight, but other then that open air conductors can take more then what the NEC specifies in both tables 16 and 17.

To ask, you mention "feels warm to the touch", what temperature are you referencing? 137*F is painfully warm.
 
mbrooke said:
The test was worth it, but it will take a lot longer for the wire to degrade. One major event indicating breakdown is "plasticizer migration" (worth researching).

There are a few free UL reports that did testing on NM wire as part of over driven staples, I will find them and post them.
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ok, but in the study of forceful destruction i can see why letting it cook for days or weeks is a good educational exercise, but how does this play into the ampacity #'s as we know them today (nec2012)? i mean, i can watch romex turn to dust just by leaving it exposed to sunlight during the summer, the UV will destroy it in no time, but this is not very beneficial in developing ampacity #'s. the NEC is about rules and #'s that make sense for proper installation and use with some safety tolerance for faults. i suspect once a wire gets itself into that zone outside of proper installation and use, perhaps by a fault for whatever reason, the ampacity table likely no longer has relevance because the fault, it it were to do damage or create a fire, would do that regardless of ampacity #'s.

i kinda went on tanget with this free air and baking test. those are odd conditions that are likely to not be prevented by way of ampacity #. my sandwich test is to see if a "nec worse case scenario"can produce any crazy temps of the wire, and from there we can evaluate if those temps will be harmful to the surroundings.

somewhere out there was a post about a store ceiling catching fire, it was stated that the 240v "romex" line had migrated into the insulation bay in the ceiling and basically covered itself with the blown-in insulation, and thats where the visual damage was, and some had concluded that due to the coverage of the insulation the temps rose too high causing the fire. but oddly, no forensics to see if the wire itself may have been faulty at that location, i could not see why the temps on the wire, even under the loose insulation, would climb so high that it would cause fire. ocpd was not faulty. and sure, the temps may have gone up to start the fire, but perhaps not because it was under loose insulation.

so, it is quite impossible to account for all the odd situations that may cause an issue, its just not possible, but what we can do (nec) is write rules and #'s that make sense given proper installation and use. 20A ocpd on #14 romex (either change ampacity #'s or allow the 75C column), seems ok to me (maybe apply voltage drop rule to limit run size, whatever), but we'll see what the sandwich test show for temps, i am not expecting a "oh geez" moment.
 
FionaZuppa said:
<snip>

and just wanted to point out, temp alone doesnt mean too much. its energy that matters. a thin wire that is hot may not have enough energy to get a big piece of wood into that combustion zone, while a big wire that is giving up lots of heat energy at a lower temp than that thin wire could be bad for that piece of wood.
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Important point.

In addition to that, the temperatures that matter are comfortably higher than anything you've measured so far. The first mentions of pyrolysis I found in Googlespace were about temperatures over 100 C, although there's a conservative standard based on freak-worst-case analysis that says to keep wooden building materials near a stove below 170 Fahrenheit.
 
mbrooke said:
Found the one from UL, starting at page 41 where a controlled degradation test is done by subjecting the wire to high temperatures:


https://www.nfpa.org/Assets/files/AboutTheCodes/70/Investigation_Damage_Degradation_NMCables.pdf
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an interesting article. i read the whole thing. the degradation of breakdown voltage due to aging is interesting. but nothing in here that i can see that would be a good metric for the existing ampacity #'s. it gave me a better understanding as to how NM wire degrades over time with temp as a factor. in summary, the colder the NM can stay the slower the degradation rate.
 
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