Interuption rating

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Someone tried to explain the fault ratings listed on brealers and I dont recall the details.   Seems I had it in a seminar, might have fallen asleep.  I see differe3nt ones on different brands,,,, is this indicator limit to be able to be connected to large trannys with hi available fault?www.urkafarms.com
Reply:

Originally Posted by Sberry

Someone tried to explain the fault ratings listed on brealers and I dont recall the details.   Seems I had it in a seminar, might have fallen asleep.  I see differe3nt ones on different brands,,,, is this indicator limit to be able to be connected to large trannys with hi available fault?
Reply:I was on my way to church. In a hurry.  SqD has 10000, I see 22k on some GE.www.urkafarms.com
Reply:I was just wondering at what level they needed to change breaker rating at?  Wondering if is simply sized according to tranny and what factor is line voltage behind it?   I am having trouble with it due to lack of familiarity for sure.  It's not so much an issue with single phase small service and they have a relatively small fuse on the line side 9f the Trans.www.urkafarms.com
Reply:https://www.eaton.com/content/dam/ea...ing-rating.pdfhttps://electricalengineeringresourc...ontrol-panels/https://forums.mikeholt.com/threads/...imply.2565675/https://www.ecmweb.com/content/artic...eaker-markingsLast edited by danielplace; 10 Hours Ago at 05:18 PM.
Reply:Very good.  I am opening some of them now, the last one seems maybe I look at earlier,,,, by earlier maybe 10 years,, hawww.urkafarms.com
Reply:Very good Danial.  The 4 step talks about panel design but it is or especially step 2 and 3 I elude to in some of my babble about circuit fundamentals but tryt to figure ouit the ultimate laymans terms for this.   My thing is,,,, in the general discussion a guy saysd,,, all the breaker does is protect the building wire,,, and while its true it may,,,, careful choice of that word here,,, the breaker also may and often does provide the fault protection for the connected equipment.   A lay version is this,,,, 15 A power strip plugged in to 20A circuit.  The little reset is thermal, its not a magnetic breaker, the connected equipment must still rely on the circuit breaker for its internal fault protection.  The same basic principles apply to most basic equipment, say air comp or pressure washer.  The fact that it complies is the stamp so to speak, manufaturer doesnt have to have every unit inspected but the thing dont get UL or NEMA unless it does.    Basically allows mfg part to be load calc for thermal and then must be sized for shorts.  Lamp fixture a great example,,, got an edison base, can only screw 100 or 200 watts in, wont overheat the 16 wire, may be connected to a 20A circuit.   The second linc was the generic version I was looking for, I am going to read a bit thru some of the others, not that I would understand it but reading it is a start.Last edited by Sberry; 9 Hours Ago at 06:13 PM.www.urkafarms.com
Reply:Another reverse version is we basically size the circuit then we can choose components to meet the short circuit,,,, can be as simple as sizing the wire for controls,  or can design the circuit then tailor the breaker.   I want to read as to how this applies to higher fault currents.  Note the 3rd note in step 3,, if fault is provided by feeder circuit.Last edited by Sberry; 9 Hours Ago at 06:21 PM.www.urkafarms.com
Reply:I get blurry in a hurry readding that bussman back and forth.  As it might relate to an installer or circuit designer here,,, sort of diy like me is,,, air conditioning circuit.  Its why they reccomend following the suggested circuit and breaker size.  The smaller wire if long enough actually is a current limiting factor in the first half of the start cycle.   It also basically says,,,,, put too big a wire downstream and provide for such a violent fault due to bigger current carrying capacity and ruin the breaker,,, hawww.urkafarms.com
Reply:I really should remove the big fat wire the helper put to my chop saw, it just needs the current limiting effect of some smaller wire, in a sense the circuit so good that it just keeps sucking it up.   An engineer and or a true electrician would prolly splain it different and have more korrect explanation but thats "kinds what happens" to the circuit so to speak.  If I am not mistaken or have the capacity so explainso,,, fwiw, its why the smaller sized wire for a welder circuit is not a real bad thing.  say you got 50 ft of 10 and chop it with an axe,,, how much less damage than a 6?Last edited by Sberry; 8 Hours Ago at 06:54 PM.www.urkafarms.com
Reply:What makes it scary is,, I got a dimwit at church I try to splain he shouldnt get a shock from his steel work bench.  He is a smart guy, dam near a genius so he knows more than most people do and does know electric theory better than me for sure but cant grasp the podge of panels with the diy and missing link makes this whole place a seething neutral and missing short circuit.  Something to be said for gfci at the panel for sure but sheet,  Impossible to splain that there is a reason its not drawing more than 20A and that this connection needs to be rated in the hundreds,, all they can see is the 20 on the breaker.   I had half azz customers and even got to watch the parts house or splain it for I order, its ok to ask to sub but you got to ask,,,, I already sized all this shate and you deliver a different wire etc.www.urkafarms.com
Reply:I brezed thru the Holdt forum,,,, that was really good,,, as a fwiw how it could appl;y here is in some cases series rating, a common 2 pole connected with main lug panel is not following a main listed at 22K,,, or backfeeding a breaker as a main.  As they point out, not such a problem on a sub.www.urkafarms.com
Reply:Define tranny.Is your tranny a cross dresser, a surgically converted person, or something else?In breaker ratings, they are rated to match the supply power source.The FPE circuit breakers were most notorious, in short circuit situations breaker points would weld, making it impossible for them to break the circuit, meltdown, or fire resulted.The ability of a breaker to open in a short circuit situation is relative to the current available to inrush at short circuit. The power company might rate available fault current at 22000 amps. By NEC rules, your service overcurrent device must be rated above that.Individual circuit breakers already protected by a bigger device don't need ratings as high.It is a staggeringly complicated formula few electrical engineers could calculate. When an inspector demands, & latest code, you are supposed to post the number, call the power company. They give a number. Farther from sub station, lower the max short circuit available power.An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Reply:Something I was wondering and they eluded to, cant always book determine the actual but, there must be a general factor for rating it agasinst the tranny.  I can see the poco not wanting a heavy tranny idle rfor small loads but it might be a safety factor to some extent.  I mean I got 400 service and a 15K tranny.www.urkafarms.com
Reply:It is a staggeringly complicated formula few electrical engineers could calculate. When an inspector demands, & latest code, you are supposed to post the number, call the power company. They give a number. Farther from sub station, lower the max short circuit available power.
Reply:

Originally Posted by Sberry

Something I was wondering and they eluded to, cant always book determine the actual but, there must be a general factor for rating it agasinst the tranny.  I can see the poco not wanting a heavy tranny idle rfor small loads but it might be a safety factor to some extent.  I mean I got 400 service and a 15K tranny.