NEC Changes For #14 Ampacity

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mbrooke said:
Which doc though?
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UL 489 specifies the trips.

Eaton TB01200003E.pdf has their trip curve. max-min for x1.25 is within UL 489 testing for UL 489 ambient of 40C. sadly, its done under one temp only, there really needs to be a UL test that has several ambients, perhaps three below and three above 40C, like 10/20/30/40/50/60/75

UL 489 Parameter
Calibration
100% of rating – hold
135% of rating - trip in one hour (<50A)
200% of rating - trip in 2 min. max. (<30A)

mbrooke said:
As an example, BS7671 which applies to the United Kingdom: 2.5mm2 (slightly larger then 2.08mm2 14 gauge) Twin and Earth (Euro equivalent to romex) is rated 27 amps when stapled to a wood stud having no insulation, 20amps when one side of the cable is resting against insulation and 13.5 amps with the cable completely covered in insulation. The conductor operating temp is assumed to be 70*C. If we were to compare these values to 14 gauge wire, we would roughly get 25 amps, 18.5 amps and 10.5 amps. Thus, the European codes require NM wire to be kept at current ratings lower then our NM wire when completely covered in insinuation and higher rating when not.
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so, lets say 20A on ~#14. in US thats 2400VA, in UK its 4800VA !!
so they can deliver 2x the power as we can using "same" wire.

i was saying at 2400VA in UK (which is what we can deliver in US) the amps in UK would be half and thus 1/4 the heat.
does UK have a 4kVA hairdryer? that might melt hair??
 
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FionaZuppa said:
UL 489 specifies the trips.

Eaton TB01200003E.pdf has their trip curve. max-min for x1.25 is within UL 489 testing for UL 489 ambient of 40C. sadly, its done under one temp only, there really needs to be a UL test that has several ambients, perhaps three below and three above 40C, like 10/20/30/40/50/60/75

UL 489 Parameter
Calibration
100% of rating – hold
135% of rating - trip in one hour (<50A)
200% of rating - trip in 2 min. max. (<30A)
Click to expand...


Which would mean at 134% (134% of 15=20.1) the breaker is not required to trip. In reality most trip before that, but holding at 125% is not unheard of.


so, lets say 20A on ~#14. in US thats 2400VA, in UK its 4800VA !!
so they can deliver 2x the power as we can using "same" wire.
Click to expand...

Correct


i was saying at 2400VA in UK (which is what we can deliver in US) the amps in UK would be half and thus 1/4 the heat.
does UK have a 4kVA hairdryer? that might melt hair??
Click to expand...


They do not install larger wires for the load, they still size wire like we do. They will either add more low draw items per circuit adding up to 4,800 watts or run one dedicated circuit to say a 4.5kw appliance like water heater, cooktop, AC, ect. In the UK a 4.5kw load (like a cooktop) could see 1.5mm2 (no insulation) 2.5mm2 (touching insulation) or 6mm2 (in dense insulation). Where cables are not in contact with thermal insulation they are allowed to dissipate a lot more heat then table 310.15. An example would be 3,800 watt load drawing 16 amps which can legally be wired in 1mm2 wire (a bit larger then 18 gauge) provided there is no thermal insulation around the wire. In the NEC the same scenario would require 2.08mmm2 (14 guage) wire, and if considered a continuous load (20amps) would require 3.31mm2 wire (12 gauge). So as you can see in NEC is automatically assuming something between touching and completely covered in insulation.
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mbrooke said:
FionaZuppa said:
Which would mean at 134% (134% of 15=20.1) the breaker is not required to trip. In reality most trip before that, but holding at 125% is not unheard of.
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i believe UL489 #'s are "at or less than time" tests, which would fall within the manufacturer's published trip curves? 135% would have to trip in under 1hr to meet UL489 spec ??
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mbrooke said:
FionaZuppa said:
Correct, but 134% is less then 135%, so a breaker could legally hold forever. In reality breakers trip well before that but usually over 100%.
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well, i would classify that as outside of the trip curve and thus faulty. perhaps the NEC should have a statement about it. the UL489 only shows that the trips are within the trip curve, but the trip curve itself defines the operational function of the device. a gray area perhaps, thus my suggestion that temp/mag technology is like from pyramid days and we have seen little advancement since.
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That is why manufacturers' data shows two curves, with the characteristics of any given test sample falling somewhere between the two curves.
The specification that a unit must carry 100% indefinitely, coupled with production tolerances, tells us that a typical sample will carry some higher current indefinitely took.
 
FionaZuppa said:
mbrooke said:
well, i would classify that as outside of the trip curve and thus faulty. perhaps the NEC should have a statement about it. the UL489 only shows that the trips are within the trip curve, but the trip curve itself defines the operational function of the device. a gray area perhaps, thus my suggestion that temp/mag technology is like from pyramid days and we have seen little advancement since.
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Electronics would give far superior tolerances (even argued better protection because GFP could be employed), but this adds another failure mechanism.
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GoldDigger said:
That is why manufacturers' data shows two curves, with the characteristics of any given test sample falling somewhere between the two curves.
The specification that a unit must carry 100% indefinitely, coupled with production tolerances, tells us that a typical sample will carry some higher current indefinitely took.
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Meaning like this....?

~RJ~
 
FionaZuppa said:
its a std trip graph. left side min, right side max. breaker should trip no less than min, no more than max. its crappy control if you ask me.
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For an experiment yes, but come real world its the worse/best case scenario at the published temperature. BTW, while this is an extreme example, it proves a point ambient temperature does have an effect:


http://goodsonengineering.com/wp-co...ker-Performance-in-Depressed-Temperatures.pdf


I know that its difficult for many to grasp that breakers can hold current over their listed handle rating but its just what comes with thermal magnetic breakers.
 
mbrooke said:
For an experiment yes, but come real world its the worse/best case scenario at the published temperature. BTW, while this is an extreme example, it proves a point ambient temperature does have an effect:


http://goodsonengineering.com/wp-co...ker-Performance-in-Depressed-Temperatures.pdf


I know that its difficult for many to grasp that breakers can hold current over their listed handle rating but its just what comes with thermal magnetic breakers.
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so two comments:
  • NEC should not allow breaker panels to be located outside directly exposed to outside ambient where any one ocpd is of the thermal/mag type
  • these ancient mag/thermal ocpd's need have a sunset date applied, lets say 1Jan2021
 
FionaZuppa said:
so two comments:
  • NEC should not allow breaker panels to be located outside directly exposed to outside ambient where any one ocpd is of the thermal/mag type
  • these ancient mag/thermal ocpd's need have a sunset date applied, lets say 1Jan2021
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I respectfully disagree. I think the technology while imperfect around the edges is ok.
 
changing ambient affects the safety factor of the ocpd. not so when i turn on my headlights in my car. if ambient affected healights so that when it was 105F outside and i turned on the lights and they blew out, thats bad, or if its 29F outside and when i turn them on they give a dismal glow, not good.
trip points are not well controlled, time to trip varies above rated #.

how is this good control?
 
Even electronic trips will have an uncertainty band. It will just be smaller.
Some would say that the temp dependence of the trip point is a good thing as it follows the temp rated ampacity of the loads and wiring.
 
FionaZuppa said:
changing ambient affects the safety factor of the ocpd. not so when i turn on my headlights in my car. if ambient affected healights so that when it was 105F outside and i turned on the lights and they blew out, thats bad, or if its 29F outside and when i turn them on they give a dismal glow, not good.
trip points are not well controlled, time to trip varies above rated #.

how is this good control?
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The thermo properties of headlamps are very different. The level of heat transerr, material, ect is different.
 
This discussion is questioning serious fundamentals for me....

I'm ok with the thermal / ampacity experiment , it makes sense , the details are irrefutable

But as applied to an OCPD , i don't get it. Why are they Thermal Magnetic, when the thermal part seems unreliable ?

Why are the magnetic qualities fixed in our resi mini breakers, when they can be adjusted to multiple applications?

Why are mag trips not an NRTL requirement ?

~RJ~
 
romex jockey said:
This discussion is questioning serious fundamentals for me....

I'm ok with the thermal / ampacity experiment , it makes sense , the details are irrefutable

But as applied to an OCPD , i don't get it. Why are they Thermal Magnetic, when the thermal part seems unreliable ?

Why are the magnetic qualities fixed in our resi mini breakers, when they can be adjusted to multiple applications?

Why are mag trips not an NRTL requirement ?

~RJ~
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I have those same questions, and I thank you for asking them. :)

Its interesting to note that where a short circuit is guaranteed to clear a breaker magnetically, the cable can be permitted to have a higher operating temperatures if my thinking is correct.
 
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