Circuit breaker ratings
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Don The fusing current for 18 AWG wire is 83 amps.? This is the point where the copper wire is hot enough to melt.? I found this info here:?? This is just over 2 times the must trip current rating of a 20 amp circuit breaker.?? For the skinny on circuit breakers, see:? According to the above link, a 20 amp circuit breaker must support a 20 amp current but must trip at 200% of rated current within two minutes.?? Since you brought up the electric code in Britton, just what is it that you like about it? Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Friday, July 12, 2024 at 08:16:16 PM CDT, don Root <drootofallevil@...> wrote:
Jim ?yes mostly ?? I guess you are responding to? ?Same sort of goes for radios of old. ?I blame the NEC++ ?for allowing a? 0.35 amp radio to be *protected* by the 15 amp house fuse ? ? Quibbling ?¡. ¡°to the outlet³§¡± I support the good practice to ??¡°add a fuse to a consumer radio¡± but going back to NEC code you need to fuse every time you reduce wire size/rating unless upstream protects it too. ?But plug-in stuff has been immune from the NEC ideas, but they still get ULs blessing somehow .? A wired in transformer must be fused, but a plug transformer ..your handy powerstat doesn¡¯t . I say it is all in the business politics of who sits on the board/ committee etc. but I should not start that here.? Seems to me fusing in Britain is more sensible.. in that way ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Friday, July 12, 2024 3:30 AM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? Don Whatever is used as a circuit protection device, it is there to protect the hidden wiring from the distribution panel where the fuse or circuit breaker is located to the outlet, it is not used to protect the load.? It is good practice to add a fuse to a consumer radio when it is in for repair but few appliances have such protection.?? ? I believe that our vacuum cleaner has a thermal circuit breaker.? Not sure about the microwave oven or the fridge but they are both close to the 15 amp rating of outlets protected by 15 amp circuit breakers.? I live in Hot Springs, Arkansas.? The local electric code does not allow for anything smaller then 12 AWG wire so the smallest circuit breaker allowed is 20 amps. Regards. Jim ?? -- don??? va3drl |
¿ªÔÆÌåÓýJim, ?interesting, and I get the jist, ?but I wonder what the point is. Anyhow, as I read stuff, #18 copper will melt [1000 C nom] at 83 amps yes ,but that happens in 10s , not 2 minutes. ?That would be the same heat/temp [ I^2 *t ] ?= about ??25A for 2 min. I don¡¯t know when insulation turns to carbon, but I¡¯m getting worried now. Maybe I goofed-up? And I have lost my point now too.? My past understanding was that grounding conductors were based on fusing temps, but conductors with insulation were somehow based on the insulation. I have no Idea what it can take short term. ? ? RE????? According to the above link, a 20 amp circuit breaker must support a 20 amp current but must trip at 200% of rated current within two minutes.?? Ya ,that is a most common criteria, and seems rather High. It seems that this was instigated back in fuse only days, and fuses that got too hot would get tired [flip on a big string of tungsten lamps] and fail.? Thermal elements of breakers also heat up in normal current service so in that condition it wont take so much to trip them, so the 200% is a practical number ? ? Re ?code in Britton? ?¡????????? ?fuses in plugs ? ? ? ? ? ? ? ¡¡.»å´Ç²Ô ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Saturday, July 13, 2024 12:57 AM To: [email protected] Subject: [HallicraftersRadios] Circuit breaker ratings ? Don The fusing current for 18 AWG wire is 83 amps.? This is the point where the copper wire is hot enough to melt.? I found this info here:?? This is just over 2 times the must trip current rating of a 20 amp circuit breaker.?? ? For the skinny on circuit breakers, see:? According to the above link, a 20 amp circuit breaker must support a 20 amp current but must trip at 200% of rated current within two minutes.?? ? Since you brought up the electric code in Britton, just what is it that you like about it? Jim ? ?
? -- don??? va3drl |
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Don There are typical specs for a particular class of circuit breaker and then there are worst case general specs for all circuit breakers.?? AFAIK, there are two types of circuit breaker, thermal and magnetic.? The thermal types take some time for the heated sensor to trip the circuit breaker mechanism.? This is desirable to reduce nuisance tripping.? Not so with the magnetic circuit breaker.? There is no thermal delay but a time delay is still possible.?? Heinemann circuit breakers, for example, are magnetic but the pole piece is a iron slug sealed in a brass tube with a spring and a viscus fluid.? As the current through the circuit breaker reaches the rated current, the iron slug will move against the spring in a time determined by the fluid.? ?The breaker will not trip at 100% of the rated current.? At 120% of rated current or above, the breaker will trip.? Any current through the circuit breaker that is well above the rated current will cause the circuit breaker to trip immediately even though the iron pole piece is not in the desired position. You will have to check the timing curves for a particular circuit breaker to determine how fast a breaker will trip at a certain percentage of overload.? I would think that at 4X rated current, any good circuit breaker would trip immediately. As for fused plugs in the U.S. they are available, see? Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Saturday, July 13, 2024 at 11:46:38 AM CDT, don Root <drootofallevil@...> wrote:
Jim, ?interesting, and I get the jist, ?but I wonder what the point is. Anyhow, as I read stuff, #18 copper will melt [1000 C nom] at 83 amps yes ,but that happens in 10s , not 2 minutes. ?That would be the same heat/temp [ I^2 *t ] ?= about ??25A for 2 min. I don¡¯t know when insulation turns to carbon, but I¡¯m getting worried now. Maybe I goofed-up? And I have lost my point now too.? My past understanding was that grounding conductors were based on fusing temps, but conductors with insulation were somehow based on the insulation. I have no Idea what it can take short term. ? ? RE????? According to the above link, a 20 amp circuit breaker must support a 20 amp current but must trip at 200% of rated current within two minutes.?? Ya ,that is a most common criteria, and seems rather High. It seems that this was instigated back in fuse only days, and fuses that got too hot would get tired [flip on a big string of tungsten lamps] and fail.? Thermal elements of breakers also heat up in normal current service so in that condition it wont take so much to trip them, so the 200% is a practical number ? ? Re ?code in Britton? ?¡????????? ?fuses in plugs ? ? ? ? ? ? ? ¡¡.»å´Ç²Ô ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Saturday, July 13, 2024 12:57 AM To: [email protected] Subject: [HallicraftersRadios] Circuit breaker ratings ? Don The fusing current for 18 AWG wire is 83 amps.? This is the point where the copper wire is hot enough to melt.? I found this info here:?? This is just over 2 times the must trip current rating of a 20 amp circuit breaker.?? ? For the skinny on circuit breakers, see:? According to the above link, a 20 amp circuit breaker must support a 20 amp current but must trip at 200% of rated current within two minutes.?? ? Since you brought up the electric code in Britton, just what is it that you like about it? Jim ? ?
? -- don??? va3drl |
¿ªÔÆÌåÓýJim, ??going back some years, MOST situations outside of equipment had thermo-magnetic trips to protect from overloads as well as short circuits. But yes? Some large breakers were magnetic, with a ¡°dashpot¡± to try to replicate thermal I^2*t ? Things have changed over the years , probably a chip would do a good job.. if we could only trust them, but your trusty 1960 washing machine? might tire out slowly? but the new ones just say error 888 .. buy a new board for only 1000 bucks , and it does that the night before the wedding or some long vacation. ???Sorry for the diversion to a rant. Oh yes back to a 35 mA or 55mA into a transformer radio being left ?at the mercy of a nominal 15A breaker ..? if the filter cap shorts, everything in the line of fire fries too until something burns open or all burns down.. maybe right to the foundation?? ..more ranting , I got up too early. and found me on the wrong side of the bed! ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Saturday, July 13, 2024 1:45 PM To: [email protected] Subject: Re: [HallicraftersRadios] Circuit breaker ratings ? Don There are typical specs for a particular class of circuit breaker and then there are worst case general specs for all circuit breakers.?? ? AFAIK, there are two types of circuit breaker, thermal and magnetic.? The thermal types take some time for the heated sensor to trip the circuit breaker mechanism.? This is desirable to reduce nuisance tripping.? Not so with the magnetic circuit breaker.? There is no thermal delay but a time delay is still possible.?? ? Heinemann circuit breakers, for example, are magnetic but the pole piece is a iron slug sealed in a brass tube with a spring and a viscus fluid.? As the current through the circuit breaker reaches the rated current, the iron slug will move against the spring in a time determined by the fluid.? ?The breaker will not trip at 100% of the rated current.? At 120% of rated current or above, the breaker will trip.? Any current through the circuit breaker that is well above the rated current will cause the circuit breaker to trip immediately even though the iron pole piece is not in the desired position. ? You will have to check the timing curves for a particular circuit breaker to determine how fast a breaker will trip at a certain percentage of overload.? I would think that at 4X rated current, any good circuit breaker would trip immediately. ? As for fused plugs in the U.S. they are available, see? Regards, Jim -- don??? va3drl |
Jim Whartenby
don Root