NEC Changes For #14 Ampacity

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romex jockey

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This bears consideration......

This bears consideration......

Mr Jockey, I found this gem :D:thumbsup::

You most certainly did Mr MBrooke....


http://paceforensic.com/pdfs/newsletter/KeepingPace-37.pdf

In this newsletter first issued in 1986, I pointed out the differences between American
circuit breakers and European circuit breakers. The European circuit breakers were much
more sensitive to arcing currents, and much more likely to trip quickly enough to prevent
an arcing fire. I began a lengthy campaign to get American circuit breakers improved. In
1993, the circuit breaker industry agreed to make common circuit breakers more sensitive,
with a magnetic trip averaging 10X. Some of them had been as high as 40X.

Zoots alors!
the ENTIRE ocpd industry conceded to lower mag trips in unison?

where were all the trade rag op-eds? the full page brkr manufacturer ads? the mobius strip logic threads here?

http://paceforensic.com/pdfs/newsletter/KeepingPace-15.pdf


Mr. John Halferty was Chairman of the circuit breaker manufacturer’s task force which was
formed to study my recommendation that American circuit breakers be redesigned to have
a lower magnetic trip level (be more sensitive to arcing)

There was a 'circuit breaker manufacturers task force' ????

AND, they determined lower mag trips equated to less arcing?


My Q here is simple...........Does it????


~RJ~
 

mbrooke

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You most certainly did Mr MBrooke....


http://paceforensic.com/pdfs/newsletter/KeepingPace-37.pdf



Zoots alors!
the ENTIRE ocpd industry conceded to lower mag trips in unison?

where were all the trade rag op-eds? the full page brkr manufacturer ads? the mobius strip logic threads here?

http://paceforensic.com/pdfs/newsletter/KeepingPace-15.pdf




There was a 'circuit breaker manufacturers task force' ????

AND, they determined lower mag trips equated to less arcing?


My Q here is simple...........Does it????


~RJ~


Well, if you call sparks flying from a short circuit arcing then yes, mag rip cuts the power a lot faster. The question is, however, does this equal to fire in the real world? The author makes the leap with over driven staples, and thats where the AFCI theory takes hold.
 

mbrooke

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Anyway, knitting the thread back together. I have a theory (though I could be wrong since its half- baked in progress).


Short circuit current was brought up in this thread as possibly having played a role in Ampacity tables.

So far several things have or can been established:

1. breaker magnetic trip points have gone down for reasons still not well known.

2. 240.4 D limits the over current protection on small conductors that otherwise have higher current ratings.

3. Small conductors can see the highest short circuit currents per circular mil of copper relative to larger conductors.

4. The NEC does not require that a short circuit trip a breaker magnetically, as such would still be considered code complaint.

5. Small conductors are typically stapled across wood studs and must survive short circuits without setting studs on fire.

6. In IEC based codes where magnetic trip is essentially required, smaller conductors are be permitted for the same current rating.


Thus under the NEC, cases exist where a short circuit will heat its conductor along with the bi-metal strip. In those cases the bi metal's heating must be faster to trigger effect, that being unlatching the breaker before the copper becomes hot enough to damage. Therefore the statement can be made 'under all current conditions the bi-metal must have a combined heating characteristic and heat response characteristic which shall be faster then any conductor heating which could reach a threshold capable of thermal damage' I would however imagine (guess) its not linear despite being an inverse characteristic.

For example: 30 amps of over current initiating an unlatch in 900 cycles resulting in say a 15*C conductor rise may not exhibit the same conductor rise if the same bi-metal naturally cleared 160 amps in 9 cycles, as it could be higher then 15*C. Its just a guess, but in that case it would make sense why smaller conductors have a a lower OCPD rating vs current carrying capacity. It may also explain why OCPD manufactures decided to lower the magnetic trip values. 2,500 amps cleared via magnetic trip vs thermal trip makes a difference in any case.


Here is a paper on short circuit withstand and heating of conductors:

http://www.cooperindustries.com/con...ductor_Protection_Wire_Cable_Protection_2.pdf

Thus if the above is true, the wire must have a lower OCPD regardless of its ability to carry current 24/7 which would explain the one correlation to K factor.

..........................................................................................................



The above of course throws one thing under the buss: motor circuits.


I can legally have #14 on a 40 amp breaker. The magnetic trip value on average is 15x40= 600amps and can certainly be higher. In most runs a ground fault will rely on the bi-metal (over load protection), one that is designed around 40 ampere rated conductor.


Thus, how is this ok? Does higher current resulting in faster mi-metal heating which result in less of a temp rise? What is the relationship? As you can see in contradicts the above. Anyone know why that is? :?:dunce::?
 

ActionDave

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Anyway, knitting the thread back together. I have a theory (though I could be wrong since its half- baked in progress).


Short circuit current was brought up in this thread as possibly having played a role in Ampacity tables.

So far several things have or can been established:

1. breaker magnetic trip points have gone down for reasons still not well known.

2. 240.4 D limits the over current protection on small conductors that otherwise have higher current ratings.

3. Small conductors can see the highest short circuit currents per circular mil of copper relative to larger conductors.

4. The NEC does not require that a short circuit trip a breaker magnetically, as such would still be considered code complaint.

5. Small conductors are typically stapled across wood studs and must survive short circuits without setting studs on fire.

6. In IEC based codes where magnetic trip is essentially required, smaller conductors are be permitted for the same current rating.


Thus under the NEC, cases exist where a short circuit will heat its conductor along with the bi-metal strip. In those cases the bi metal's heating must be faster to trigger effect, that being unlatching the breaker before the copper becomes hot enough to damage. Therefore the statement can be made 'under all current conditions the bi-metal must have a combined heating characteristic and heat response characteristic which shall be faster then any conductor heating which could reach a threshold capable of thermal damage' I would however imagine (guess) its not linear despite being an inverse characteristic.

For example: 30 amps of over current initiating an unlatch in 900 cycles resulting in say a 15*C conductor rise may not exhibit the same conductor rise if the same bi-metal naturally cleared 160 amps in 9 cycles, as it could be higher then 15*C. Its just a guess, but in that case it would make sense why smaller conductors have a a lower OCPD rating vs current carrying capacity. It may also explain why OCPD manufactures decided to lower the magnetic trip values. 2,500 amps cleared via magnetic trip vs thermal trip makes a difference in any case.


Here is a paper on short circuit withstand and heating of conductors:

http://www.cooperindustries.com/con...ductor_Protection_Wire_Cable_Protection_2.pdf

Thus if the above is true, the wire must have a lower OCPD regardless of its ability to carry current 24/7 which would explain the one correlation to K factor.

..........................................................................................................



The above of course throws one thing under the buss: motor circuits.


I can legally have #14 on a 40 amp breaker. The magnetic trip value on average is 15x40= 600amps and can certainly be higher. In most runs a ground fault will rely on the bi-metal (over load protection), one that is designed around 40 ampere rated conductor.


Thus, how is this ok? Does higher current resulting in faster mi-metal heating which result in less of a temp rise? What is the relationship? As you can see in contradicts the above. Anyone know why that is? :?:dunce::?
You're either nuts or you need to get more sleep.
 

mbrooke

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Technician
You're either nuts or you need to get more sleep.


Im sure my lack of sleeping has heightened my thinking :cool: :lol: :p


But think about it?

At 50 amps it could take an hour for a 40amp breaker to trip. 50 amps on #14 for an hour will heat it considerably. Now what if it was 80 amps for 6 minutes? 125 amps for 2 seconds? How hot would the wire be then?

The thermal curve for a 40amp breaker is much higher then a 15 amp breaker. Not saying the NEC is wrong, Im Im curious how it works.
 

romex jockey

Senior Member
Location
Vermont
Occupation
electrician
it's a long mag trips story.....

it's a long mag trips story.....

Anyway, knitting the thread back together. I have a theory (though I could be wrong since its half- baked in progress).

Let's see where we can go with this then Mr MBrooke.....


The crux being as you've stated>>>>>

Thus, how is this ok? Does higher current resulting in faster mi-metal heating which result in less of a temp rise? What is the relationship? As you can see in contradicts the above. Anyone know why that is? :?:dunce::?

The normally wired motor CCC's you speak of do assume more current, thus more of a magnetic field.

However, it's usually considered to have nominal heat rise , which is why overload protection (430.32) is mandated.

Duty cycle is a concern, and we'll find these lesser conductors being compliant for welders in art 630 as well

The jist being two fold here......heat vs. time juxtaposed with heat vs. incendiary levels

<<<<<<<<<<<<<<*>>>>>>>>>>>>

Somehow , the industry latched onto the idea that 'arcing' constituted anything electrically incendiary.

The result was a number of 'arc detection patents' some 20 odd years ago. (the paper details 16 of them)

Oddly enough , this flurry of activity came about after ul itself established Glowing Connections as the chief incendiary culprit.....

<<<<<<<<<<<<<<<<<<<<*>>>>>>>>>>>>>>>

At the same time , we know various orgs solicited for lower mag trips , not only my last posts breaker manufacturer coalition, but also the Electronic Industries Association >>>

EIA had studied the issue of arcing fires and determined that some level of additional protection from effects of arcing faults would be beneficial. EIA attempted to improve protection by requiring that the instantaneous trip level of a circuit breaker be reduced to the 85 A level

within the same paper>>>

Hazardous arcing.For arcing at current levels of about 75 amperes and above, the AFCI will trip. Commercially available AFCIs will actually operate at some level below 75 amperes. The AFCI will operate faster than a fuse or circuit breaker under short-circuit overcurrent conditions up to about 125 amperes

Their wishes came to fruition, as seen here

So, piecing all this together, we've lower mag trips , but the problem of motors spiking out of their range. This is why i ask how proximal the serving xformer is to those afci complaint refers , OR conversely, how far from a GC.....

This sites gracious author opining in inescapable simplicity summing it up>>>>


Okay the way I see it, the paper is saying that loose connections, which Dr. Engel calls glowing connections are not a hazard but they becomes hazardous the moment a ground fault or short circuit develops. Is this paper implying if I used a 20A fuse or standard circuit breaker, the protection device will not clear the fault before a fire but an AFCI will?

Are you telling me that there is no fire hazard with loose connections and that it’s only a problem when the short circuit or ground fault occurs? For all of these years, I thought the loose connections caused the fire and the short circuit or ground fault caused the protection device to operate, but not before the fire.




Can U hear Clint Eastwood sayin'......'do ya feel lucky punk?' :)

~RJ~
 

mbrooke

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Technician
Let's see where we can go with this then Mr MBrooke.....


The crux being as you've stated>>>>>



The normally wired motor CCC's you speak of do assume more current, thus more of a magnetic field.

However, it's usually considered to have nominal heat rise , which is why overload protection (430.32) is mandated.


Thats true, but my question is what happens when the short circuit or ground fault is overload status to the breaker? Ie, it does not trip magnetically.



Duty cycle is a concern, and we'll find these lesser conductors being compliant for welders in art 630 as well

The jist being two fold here......heat vs. time juxtaposed with heat vs. incendiary levels

Ok, that makes more sense. But I still wonder how it works out in the real world. Does a 400 amp current heat the wire more or less then a 150 amp current on that same 40amp breaker? Yes tripping is faster, but is the wire cooler, warmer or the same?



........................<<<<<<<<<<<<<<*>>>>>>>>>>>>....................................................







Somehow , the industry latched onto the idea that 'arcing' constituted anything electrically incendiary.

The result was a number of 'arc detection patents' some 20 odd years ago. (the paper details 16 of them)

Oddly enough , this flurry of activity came about after ul itself established Glowing Connections as the chief incendiary culprit.....


Going off track back into AFCIs, however you are 100% correct. I can acknowledge that. The docs on the follwoing site: http://paceforensic.com/ regarding AFCIs re-label short circuits as arc faults. Yes its true that the incident energy is less via magnetic trip then thermal trip, but in any case it seems like the breaker still opens. However the author jumps to the conclusion this automatically results in fire without any evidence.

There is this by UL for the CPSC:

For arcs in electrical distribution
systems, the insulating medium is an air gap (for parting arcs), wire insulation, or any
other insulator used to separate the electrodes or line and neutral conductors. An arc will
not jump an air gap and sustain itself unless there is at least 350 V7 across the gap.
Therefore, in 120/240 Vac systems, it is difficult for arcing to cause ignition unless arc
tracking occurs, or the electrodes loosely contact each other causing a sustained arcing
fault.5


http://www.cpsc.gov//PageFiles/108737/AFCIFireTechnology.pdf


Basically a short circuit. Having a short clear at 3 cycles vs 40 cycles has never been proven to be behind 30,000 dwelling fires at that seems to be the theory that got the ball rolling on AFCIs.






<<<<<<<<<<<<<<<<<<<<*>>>>>>>>>>>>>>>

At the same time , we know various orgs solicited for lower mag trips , not only my last posts breaker manufacturer coalition, but also the Electronic Industries Association >>>



within the same paper>>>



Their wishes came to fruition, as seen here

So, piecing all this together, we've lower mag trips , but the problem of motors spiking out of their range. This is why i ask how proximal the serving xformer is to those afci complaint refers , OR conversely, how far from a GC.....

This sites gracious author opining in inescapable simplicity summing it up>>>>







Can U hear Clint Eastwood sayin'......'do ya feel lucky punk?' :)

~RJ~


When the theory came about that short circuits taking a bit longer to clear (and thus relabeled arc faults) were responsible for thousands of home fires many said lets just lower the magnetic trip threshold. And they did and I think it was a good idea in cases where high fault currents are present. However some wanted all short circuits to clear a breaker magnetically so they recommended 75amps. 75 amps was ok, but could nuisance trip AC units or some vacuums. So then they jumped on the electronics waveform analysis wagon and the modern AFCI was born.

The sad part being what was ignored, or could not be ignored... In testing all over driven staples and voltage break down involved the EGC, so a simple GFP/GFCI breaker could not only do the same, but do it better. One could still argue cords, but a built in fuse does the same. Both options were discarded DESPITE 30/50 ma GFP needed to be put into AFCIs because that was the only way to pass most of UL1699.

This is of course, as you know after someone decided to re-label short circuits as arc faults then claiming they were responsible for thousands of fires without any proof.


Kicker was in the process they openly validated almost every country on earth outside of North America already had AFCI protection with no major drop or correlation in fires since mass implementation.


See how it all comes together?
 

mbrooke

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Also, notice how in patents the inventor isnt allowed call short circuits as arcing directly, notice the quotes:



Other tests have demonstrated that “arc” short cir
cuit current flow also increases substantially instanta
neously, but to a maximum value as limited by the arc
resistance.This maximum value of “arc” short circuit
current flow has been found to vary, generally between
' about 150 amperes and 400 amperes. It has also been
found that “arc” short circuit current flow is further
characterized by being intermittent.


https://www.google.com/url?sa=t&rct...544Fkap15wL5LQ&bvm=bv.104317490,d.eXY&cad=rja
 

romex jockey

Senior Member
Location
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electrician
Good Q....

Good Q....

But I still wonder how it works out in the real world. Does a 400 amp current heat the wire more or less then a 150 amp current on that same 40amp breaker? Yes tripping is faster, but is the wire cooler, warmer or the same?

I'm sorry but, i'm unable to answer this Mr MBrooke. :(

All the variables do , however, come to mind.....

There is the CCC, as well as every joint, junction, device, and piece of equipment affected as well.

As to an OCPD's response , it really boils down to two basics, thermal and magnetic .

That's all there really is to alter , despite any nema/ul/cspc voodoo there may be

All the evidence posted (thx again) would point to the ocpd manufactures choosing the mag trip route as their blanket solution

~RJ~
 

mivey

Senior Member
FWIW, I believe I found mid/upper 100s to mid 200s on an older home we had. Seems like it was 400-600 on a newer home, maybe even 800+ at some points. Pretty anecdotal since I can't recall the exact figures. I could make some new measurements tomorrow for the fun of it if I don't forget.

I found one as low as 165 amps. Another at 188. A couple in the mid to upper 200's, the rest in the 300/400/500/600+ amp ranges. So we might could stretch that to say 10-20% of the circuits might not trip magnetically. Just one sample location though.
 

mivey

Senior Member
What ever it was it was enough to get manufactuers to change without CMP or UL mandates. Whether they were escaping liability, made a discovering in its best interest or just arbitrary reason is unknown.



No idea, however that is something I always wonder about. If UL does not require a magnetic trip, why is it even added to breakers in the first place when in theory its removal can save cost? Perhaps the question is, are the UL standards outdated?
Perhaps to get closer to conductor fusing levels?

Crunching some numbers real quick I get around 170-190 amps for #14 cu and 235-300 amps for #12 cu, which is closer to the 10-15x under discussion.
 

mbrooke

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I found one as low as 165 amps. Another at 188. A couple in the mid to upper 200's, the rest in the 300/400/500/600+ amp ranges. So we might could stretch that to say 10-20% of the circuits might not trip magnetically. Just one sample location though.

And toss a 100 foot length from breaker to furthest point and the deal is sealed.


Thats my point, it varies based on factors, but those factors are not a rarity by any means.
 

user 100

Senior Member
Location
texas
And toss a 100 foot length from breaker to furthest point and the deal is sealed.


Thats my point, it varies based on factors, but those factors are not a rarity by any means.

Yet we don't have a lot fires due to an ocpd not tripping on a long branch circuit. I get what your saying (and that was some good info/links you posted btw), but we have literally millions of long bcs (many of those #14 nm) protected by standard breakers that trip reliably everyday on those long runs before any conflagration results.
 

mivey

Senior Member
And toss a 100 foot length from breaker to furthest point and the deal is sealed.
:? What 100 foot? Those were measurements to the furthest points. The furthest point yielded 165 amps. The shortest run was a dedicated receptacle and was in the high 600's.
 

mbrooke

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:? What 100 foot? Those were measurements to the furthest points. The furthest point yielded 165 amps. The shortest run was a dedicated receptacle and was in the high 600's.

My bad :ashamed1: I thought you meant the service. :ashamed1:
 

mbrooke

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Technician
Yet we don't have a lot fires due to an ocpd not tripping on a long branch circuit. I get what your saying (and that was some good info/links you posted btw), but we have literally millions of long bcs (many of those #14 nm) protected by standard breakers that trip reliably everyday on those long runs before any conflagration results.



Exactly my point. Short circuits clear fine on thermal trip, yet the industry re-labeled these these shorts circuits as "arc faults" or "high current arcing" claiming to be behind thousands of fires each year with the scientific reasoning being they take more then a few cycles to clear.
 

romex jockey

Senior Member
Location
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Occupation
electrician
watch that staple.....

watch that staple.....

UL study

A resistance of 161 mΩ from a 14 AWG NM cable is equivalent to 50 feet (assuming a maximum
operating temperature of 90°C; at 25°C this length of cable would measure 128 mΩ for copper conductor
cable).2
If longer runs are needed for a particular application, the wire gauge can be made larger to
maintain an impedance of 128 mΩ or lower (again, measured during installation at 25°C). An evaluation
of the energy released during one half-cycle when the circuit breaker magnetic trip level and home run
resistance are both properly matched shows that there is a 2% probability of ignition of the NM cable if
arcing were to occur.

~RJ~
 
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