NEC Changes For #14 Ampacity

[mbrooke]

I'm not getting the relationship now Mr MBrooke

and i was soOOoo blissful before this thread too....

~RJ~

It goes like this. When a fault at the furthest point relies on thermal trip, there is a delay in heating the bimetal before unlatching takes place which in turn also heats the conductor. If the fault sputters or "arcs" it limits the current acutall increasing the time for the bi-metal to open. So it is necessary to factor in a certain margin of short circuit heating into the wire. However, that value can be substantially reduced on magnetic trip because it is near instantaneous and in turn the wire carries less fault current.

 

[FionaZuppa]

The thermo properties of headlamps are very different. The level of heat transfer, material, etc is different.

i am not looking at any of the properties of the device. the device (ocpd, headlamp, whatever) has to perform a funtion and has to do it well in all circumstances. -25F in Alaska to +115F where i am, i turn on the lamps and voila, i light my way, no issues.

these therm/mag ocpd's, well they dont exactly do what they are supposed to do all of the time. if my bc is 20A max then my ocpd should limit that to 20A max. i know we need the C & D trip curves for motors/inductive loads, but that can be programmed.

so maybe my next test is to do a prolonged 18A #14 NM test in a glass sandwich. if a 15A ocpd wont trip at 18A then is this a hazard? maybe even back to 20A because as in my house the panel is outside, just had 29F the other night, certainly 29F is not even close to UL489. this scenario could pose a fire hazard?

 

[mbrooke]

i am not looking at any of the properties of the device. the device (ocpd, headlamp, whatever) has to perform a funtion and has to do it well in all circumstances. -25F in Alaska to +115F where i am, i turn on the lamps and voila, i light my way, no issues.

Correct, for headlamps. Breakers as they are today are different. Manufactures give a temp tolerance and it is up to the installer to make sure the breaker is within that.

these therm/mag ocpd's, well they dont exactly do what they are supposed to do all of the time. if my bc is 20A max then my ocpd should limit that to 20A max. i know we need the C & D trip curves for motors/inductive loads, but that can be programmed.

But, just for thought, how important is it that a breaker trip at 20.01 amps in 5 seconds vs 24 amps in 5 minutes? Is such a high degree of accuracy needed in residential power systems? Would such high accuracy achieve anything else besides the elimination of 240.4 (d) in some applications?

so maybe my next test is to do a prolonged 18A #14 NM test in a glass sandwich.

I think this is a worthwhile endeavor. We have a worse case and a best case, seeing where the most common application resides is key.

FWIW regarding this I have a theory. Crunching the numbers the 90*C column in the NEC is in fact based on open air with a target temperature of roughly 120-130*F at 86*F. The restrictions like 75/60*C, 240.4 (D), 125% continuous loading are to take into account fiberglass insulation.

This is just a theory, but numbers are nudging me. Further, the clipped direct values at 90*C for 3 current carrying conductors in the IEC are about 5%-10% within the 90*C column of 310.15.

if a 15A ocpd wont trip at 18A then is this a hazard?

I would think only if it overheats the wire.

maybe even back to 20A because as in my house the panel is outside, just had 29F the other night, certainly 29F is not even close to UL489. this scenario could pose a fire hazard?

I am going to be honest. I despise panels being outside. The NFPA actually did a test on aging breakers and found that the vast majority which failed to trip were in exterior panels. UL did a residential research aging project and those breakers that failed to trip appeared to be pulled from exterior panels. Opening the breakers revealed insect infestation and corrosion. This is off topic, but unless breakers change in design I truly believe resi breakers should not be installed outdoors.

 

[FionaZuppa]

I am going to be honest. I despise panels being outside. The NFPA actually did a test on aging breakers and found that the vast majority which failed to trip were in exterior panels. UL did a residential research aging project and those breakers that failed to trip appeared to be pulled from exterior panels. Opening the breakers revealed insect infestation and corrosion. This is off topic, but unless breakers change in design I truly believe resi breakers should not be installed outdoors.

with such test data available why hasnt NEC made a rule for residential, "has to be located on a interior wall" where they include their definition of "interior", etc. this coming winter/summer i will stick a TC in my panel to see how cold/hot it can get.

 

[mbrooke]

with such test data available why hasnt NEC made a rule for residential, "has to be located on a interior wall" where they include their definition of "interior", etc. this coming winter/summer i will stick a TC in my panel to see how cold/hot it can get.

No idea.


(Probably because its not a rule that would bring in more profit) :lol:

 

[romex jockey]

Being i hail from Northern New England, i can honestly say we're a challenge to anything weather proof /resistant.

~RJ~

 

[mbrooke]

Being i hail from Northern New England, i can honestly say we're a challenge to anything weather proof /resistant.

~RJ~

Arent most panels in NE inside?

 

[user 100]

why hasnt NEC made a rule for residential, "has to be located on a interior wall"

Because it isn't needed- while it's true that exterior panelboards and cbs can be more susceptible to damage, thats not a given and the fact is is that we have many millions of them that will never have any issues/perform any differently than an interior clone.

Often when doing a panel swap it simply isn't practical to relocate a panel indoors and it is almost always more costly to the customer to do so.

I'm certain (and hopeful) that such an NEC requirement would never see the light of day- imo, it needs to be left up to the customer or the ahj.

 

[mbrooke]

Because it isn't needed- while it's true that exterior panelboards and cbs can be more susceptible to damage, thats not a given and the fact is is that we have many millions of them that will never have any issues/perform any differently than an interior clone.

Often when doing a panel swap it simply isn't practical to relocate a panel indoors and it is almost always more costly to the customer to do so.

I'm certain (and hopeful) that such an NEC requirement would never see the light of day- imo, it needs to be left up to the customer or the ahj.

I partly disagree, testing has shown higher failure rates. Corrosion aside, bugs can also get in through the weep holes and build nests/lay eggs inside the breaker. There is also the performance of breakers in very cold weather (say 0*F), but further testing would be needed to say for sure.

 

[mbrooke]

Page 31 shows the breakers from an outdoor enclosure:


http://ewh.ieee.org/cmte/pses/ffat/support/RESAReport.pdf

The other four circuit breakers, which were all made by manufacturer B, were
examined by UL. A visual inspection of the opened molded cases identified
extensive corrosion on many of the operating mechanism and spring parts.
Remnants of insect infestation were also noticeable.

BTW, from cracking open breakers in my garage the ones made by manufacture "B" appear to be GE.

 

[FionaZuppa]

Because it isn't needed- while it's true that exterior panelboards and cbs can be more susceptible to damage, thats not a given and the fact is is that we have many millions of them that will never have any issues/perform any differently than an interior clone.

Often when doing a panel swap it simply isn't practical to relocate a panel indoors and it is almost always more costly to the customer to do so.

I'm certain (and hopeful) that such an NEC requirement would never see the light of day- imo, it needs to be left up to the customer or the ahj.

why not start with new construction / new installs?

UL489 is 40C, a therm/mag 15A ocpd might hold 18A if ambient is 29F, that could be bad on say a bc that is to some outlets that never get used and theres a fault there.

no reported issues....... not yet. the NEC is abut potential issues, not just the ones that have already happened. i like this approach, within reason and with data.

 

[user 100]

why not start with new construction / new installs?

UL489 is 40C, a therm/mag 15A ocpd might hold 18A if ambient is 29F, that could be bad on say a bc that is to some outlets that never get used and theres a fault there.

no reported issues....... not yet. the NEC is abut potential issues, not just the ones that have already happened. i like this approach, within reason and with data.

I understand where you and mbrooke are coming from, but the majority of ext installs will never cause any problems- guys, down in the south, you may drive for miles and the only set up you will encounter at a residence is an outdoor panel. And probably 98% of those panels continue to hum along year after year uneventfully, and their breakers trip reliably, through sweltering summer humidity and under the load of window ac's and under the strain of electric space heaters in the winter.

The fig 14 photo shown in mbrooke's link (cool link btw), is reflective of a bad/poorly maintained install and under the circumstances shown, it would be likely that there would be damage to breakers, bussing, conductors/insulation, terminals etc- much like the ​interior panel with those few missing knockouts that becomes a toilet/house for heat seeking rodents or a palace for roaches.

Should we also ban mh disconnects also because they have a few extra spaces (which is a huge convenience for future additions) that make sp cbs/ bcs in an ext panel possible?

Remember that the NEC already has requirements for ext panels/installs that when followed effectively eliminate/reduce many of the concerns (moisture, insects, corrosion) associated with ext panelboards.

I still believe that this is more of customer/ahj issue.

 

[mbrooke]

I understand where you and mbrooke are coming from, but the majority of ext installs will never cause any problems- guys, down in the south, you may drive for miles and the only set up you will encounter at a residence is an outdoor panel. And probably 98% of those panels continue to hum along year after year uneventfully, and their breakers trip reliably, through sweltering summer humidity and under the load of window ac's and under the strain of electric space heaters in the winter.

True, but of residential fires that happen, how many of them are from faulty breakers? We dont have an exact number, however in the case of those breakers pictured had a short circuit occurred while in service a fire may have ensued.

The fig 14 photo shown in mbrooke's link (cool link btw), is reflective of a bad/poorly maintained install and under the circumstances shown, it would be likely that there would be damage to breakers, bussing, conductors/insulation, terminals etc- much like the ​interior panel with those few missing knockouts that becomes a toilet/house for heat seeking rodents or a palace for roaches.

True, but critters can still get in under the right conditions more so then an indoor panel. The rapid temperature swings can accelerate breaker's aging internally over decades.

Should we also ban mh disconnects also because they have a few extra spaces (which is a huge convenience for future additions) that make sp cbs/ bcs in an ext panel possible?

Remember that the NEC already has requirements for ext panels/installs that when followed effectively eliminate/reduce many of the concerns (moisture, insects, corrosion) associated with ext panelboards.

Reduce, but not not eliminate in its entirety. Breakers still see temp and humidity swings. Breaker internals can still get morning dew/condensation. No tests are done which grantee breakers exposed to such will have the same failure rate as those within conditioned environments.

I still believe that this is more of customer/ahj issue.

This is not to say I disagree with you, in fact I think you are correct. I do not believe the NEC need ban all outdoor panels, instead have manufactures tweak their products to better handle these conditions. Adding a fine metal or plastic screen to the arc chute opening would restrict bug infiltration while better metal alloys would inhibit corrosion. We have the technology to make a near fail safe breaker.

 

[FionaZuppa]

panels outside in south, those breakers would likely trip sooner than expected when ambients are above UL489 spec of 40C. but now i ask this Q, UL489 also gives max temp rise from 40C, which might be exceeded with small amps when ambient is 115F. so i guess i need to tape a TC to a test OCPD and in dead of summer put 10-75% load on the ocpd and see where the temp is.

 

[mbrooke]

panels outside in south, those breakers would likely trip sooner than expected when ambients are above UL489 spec of 40C. but now i ask this Q, UL489 also gives max temp rise from 40C, which might be exceeded with small amps when ambient is 115F. so i guess i need to tape a TC to a test OCPD and in dead of summer put 10-75% load on the ocpd and see where the temp is.

Maybe, but Id first test a batch of breakers from different manufactures at the same temp because each one will vary slightly in trip threshold.

 

[FionaZuppa]

Maybe, but Id first test a batch of breakers from different manufactures at the same temp because each one will vary slightly in trip threshold.

not really testing the ocpd, will try to get past the ocpd rating when ambient is hot, and will be testing the temp of the ocpd to see if it exceeds UL489, and at the same time perhaps run those amps through NM in glass sandwich.

you see any issue doing such test by using the low-v high amps of the MOT secondary?

 

[mbrooke]

not really testing the ocpd, will try to get past the ocpd rating when ambient is hot, and will be testing the temp of the ocpd to see if it exceeds UL489, and at the same time perhaps run those amps through NM in glass sandwich.

you see any issue doing such test by using the low-v high amps of the MOT secondary?

Low V will not effect the breaker, but let me think if this test needs revising.

You are still doing the fiberglass tests?

 

[mbrooke]

I came across a paper which mentions the outer jacket on NM being rated 75*C:

Around 1950, synthetic spun rayon was being permitted to replace the cotton thread in the jacket braid. Then in the early 1960’s, thermoplastic began replacing the braided jacket altogether, and by about 1970, most all NM cable had a PVC outer jacket, even though a braid was still permitted until 1984. Also in 1984, NM-B cable was developed and required to have 90°C rated individual conductors, and a 75°C outer jacket (see Fig. 4).

http://www.dli.mn.gov/CCLD/PDF/eli_bulletin_history.pdf

 

[FionaZuppa]

Low V will not effect the breaker, but let me think if this test needs revising.

You are still doing the fiberglass tests?

yes, we can use the same glass sandwich to do several tests. next up will just be NM in glass sandwich, i just need to figure best way to connect the TC

 

[mbrooke]

yes, we can use the same glass sandwich to do several tests. next up will just be NM in glass sandwich, i just need to figure best way to connect the TC

Sounds like a plan. Also, if you need any gut (innards) pics of common thermal magnetic breakers for your study I will post them. :thumbsup: