NEC Changes For #14 Ampacity

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FionaZuppa

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got the ~30lb variac today, and yep, it has that MIC smell like harbor freight ;)
next to arrive is the mot.
almost there.
 

mbrooke

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got the ~30lb variac today, and yep, it has that MIC smell like harbor freight ;)
next to arrive is the mot.
almost there.

Awesome. Just make sure the MOT is from one of those larger ovens, like an over the range. The smaller compact models may be to small.
 

mbrooke

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Excellent! :D


Thats what caught my eye, it seems these tables are being revisited again more and more. Considering cable has gone from rubber to PVC is enough by itself imo to reconsider the thermal limits of wire, especially when these tables were written 80 plus years ago. Personally, I think this may have been a driver in the CEC to get the ampacities changed.
 

romex jockey

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So it appears the older criterior is being challenged from .8 to .9 , in step with the IEC

The obvious bureaucratic opposition , who all have .1 to loose being>>>

There appears to be only one USER interest on Panel 6

~RJ~
 

mbrooke

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So it appears the older criterior is being challenged from .8 to .9 , in step with the IEC

The obvious bureaucratic opposition , who all have .1 to loose being>>>



~RJ~

There is this, even NEMA took notice 10 years ago:

https://www.nema.org/Standards/ComplimentaryDocuments/nec-iec60364.pdf


If one takes a look at the end (page 84 on the paper itself, not the viewer) they went as far as trying to apply IEC wiring tables and EFLI to US installations. Its noted in the paper that NEC wiring tables are more conservative overall:

However, the graph in Annex E of this report shows that the NEC
ampacities are consistently more conservative than those of
Chapter 5 in IEC 60364.
 

FionaZuppa

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Part Time Electrician (semi retired, old) - EE retired.
There is this, even NEMA took notice 10 years ago:

https://www.nema.org/Standards/ComplimentaryDocuments/nec-iec60364.pdf


If one takes a look at the end (page 84 on the paper itself, not the viewer) they went as far as trying to apply IEC wiring tables and EFLI to US installations. Its noted in the paper that NEC wiring tables are more conservative overall:

this kinda went full circle. we are at the point where the #'s as-is are known to be overly conservative. trying to figure out how it got like that. NEC doesnt seem to do any real-world testing on their own, its a voting committee that reads proposals, looks at submitted test data, and then decides what should be ratified into the next version of NEC. if the current method is to use the N-M calc method then show me where the N-M #'s get adjusted to arrive at new conservative #'s. this is the piece i cant find.
 

mbrooke

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this kinda went full circle. we are at the point where the #'s as-is are known to be overly conservative.

:lol: In a way it did. When it comes to exposed conduit or wire run in walls without insulation without a doubt the NEC is highly conservative. In fact if one adjusts 2.08mm2 (14 gauge) to 2.5mm2 wire clipped direct, #14 would be legally allowed to carry 24 amps continuously at 70*C.

trying to figure out how it got like that. NEC doesnt seem to do any real-world testing on their own, its a voting committee that reads proposals, looks at submitted test data, and then decides what should be ratified into the next version of NEC.

Looks to be so. What also I am wondering (and I ask anyone reading if they can help) is what drove the NEC to go from 60*C insulation to 90*C insulation in MN wire.

if the current method is to use the N-M calc method then show me where the N-M #'s get adjusted to arrive at new conservative #'s. this is the piece i cant find.

To be honest at this point I think we may never know, especially considering that the tables when originally derived were based around old rubber insulation which is where (guessing) the safety factor may have come from. Rubber insulation is pure trash when compared to THHN-THWN2. This is not to say its not a valid question, but to be honest I just dont know.

Personally, I think table 310.14 needs to be revisited and studied in depth more then ever. With wire insulation becoming better, building thermal insulation evolving, green sustainability now a concern, coupled with the volatile prices of copper; re-evaluating wire ampacity is a smart idea.

I think the NEC should go for a table based on the wire's installed ability to dissipate heat, adjusted for bundling/ambient temps, then checked against voltage drop. This imo would result in the best utilization of copper.

I also think a few new wire gauges should be created for common use applications were the actual wire current capacity tends to be higher or lower then what the typical application calls for. An example is 30 amps. In the IEC there is a bridge between 4 and 6 mm2 wire. 4mm2 is rated 26 amps in contact with thermal insulation, yet 6mm2 at 34 amps. Thus a bridge exists. In the CEC, a 30amp electric heater would also see that same gap with #12 (3.31mm2) rated 25 amps and #10 (5.26mm2) rated 35 amps. Thus, in both cases creating a new wire gauge may be a feasible investment. Something like like 4.62mm2 would be just right, allowing copper saving for a very typical current carrying requirement. This also extends to what the link mentions. If the AWG system was put in the IEC (and visa versa) electricians would in theory have more wire gauges to choose from to best suite ampacity and voltage drop.


This, of course, is meaningless without testing. This where you come in :D:)
 

mbrooke

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Edit, I notice the conversion link is down in the linked Mike Holt thread. I will post mine here instead for reference.


AWG to mm2:
 

FionaZuppa

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This, of course, is meaningless without testing. This where you come in :D:)
i am not an authoritative provider of test data, but what i am doing can be easily repeated by someone like Dayton T Brown, Inc. hah, me being a skeptic of MIC harbor freight tools i had one of their torque wrenches tested by DTB many moons ago (thanks to my dad who was at L3 at the time), the wrench was within advertised tolerance spec.

anyways, the mot showed up today, i have already taken it apart, cleaned it up good, took some Z & L readings of the coil in air and in the iron, now its sitting until tomorrow with some fresh epoxy that takes some time to set. in the iron it has Z right around 4.7ohms, gonna get warm at 25amps, but we'll likely not get that high on the primary side, etc. i'll get a piece of stranded 0 or 000 (whatever fits best) along with some lugs. hopefully by next week it will be ready for testing.
 

mbrooke

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i am not an authoritative provider of test data, but what i am doing can be easily repeated by someone like Dayton T Brown, Inc. hah, me being a skeptic of MIC harbor freight tools i had one of their torque wrenches tested by DTB many moons ago (thanks to my dad who was at L3 at the time), the wrench was within advertised tolerance spec.

Not an official authority yes, but a true person discovers for themselves. What you are doing is far from trivial in my world.

anyways, the mot showed up today, i have already taken it apart, cleaned it up good, took some Z & L readings of the coil in air and in the iron, now its sitting until tomorrow with some fresh epoxy that takes some time to set. in the iron it has Z right around 4.7ohms, gonna get warm at 25amps, but we'll likely not get that high on the primary side, etc. i'll get a piece of stranded 0 or 000 (whatever fits best) along with some lugs. hopefully by next week it will be ready for testing.

Dont forget to play around with the secondary output. Try different sizes in different winding numbers to see what gets the best volts vs amps ratio.
 

FionaZuppa

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Part Time Electrician (semi retired, old) - EE retired.
Is anybody ever going to get around to burning up some wire?

senza fretta, a tempo debito

emoticon-eating-popcorn-mh900437984.jpg
 

FionaZuppa

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AZ
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Part Time Electrician (semi retired, old) - EE retired.
I'll take that bet; but I pick the ambient and air circulation :p

you guys have not been following this thread. the testing is based on the notion that NEC has to account for worse case scenario. there is no free air testing. for those not following this thread, i'll leave it to you to go read some of the earlier posts. in summary, its a test of NM in a insulating sandwich.

This may be a spoiler, but still question how conservative it really is:
http://www.weicowire.com/image/pdf/CurrentCapacityChart.pdf
unfortunately, many of these other tables are simple wire tests and are on-par with the NEC 75 & 90C column. this thread is specifically about NM being stuck in the 60C column and #14 being stuck on a 15A ocpd (w/o regard for the allowed exceptions, which can lead to another thread for debate).
 
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mbrooke

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you guys have not been following this thread. the testing is based on the notion that NEC has to account for worse case scenario. there is no free air testing. for those not following this thread, i'll leave it to you to go read some of the earlier posts. in summary, its a test of NM in a insulating sandwich.

IMO, I think you should also run 1 sample in open air, just to get an idea of where the ampacity tables stand. Do they lean toward open air or worse case?


unfortunately, many of these other tables are simple wire tests and are on-par with the NEC 75 & 90C column. this thread is specifically about NM being stuck in the 60C column and #14 being stuck on a 15A ocpd (w/o regard for the allowed exceptions, which can lead to another thread for debate).

I think that is a good (and simple) place to start for now.
 
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