Conductor Ampacity Correction and Adjustment, NEC 2014 - 310.15. (42min:03sec)

conductor ampacity let me stretch on this and you really should stop the DVD go get yourself a glass iced tea cup coffee no take a break you know take a little nap come back I'm going to try the best I can with our guys here to try to not make it any more difficult than it probably is ready for this conductor and passing let me make a couple discussions before we get too far in it number one the impassive a conductor is defined and according with article 100 and here's what it says it's the maximum current in amperes a conductor can carry continuously under the condition of use without exceeding its temperature rating condition of use okay here we go so this is three gauge wire th H n - tube which is 90 degrees C I would go to Table three ten fifteen be sixteen and it would say ninety degrees C that wire is great 115 amps and that table is based on three current-carrying conductors and that table ampacity is based on 86 degrees Fahrenheit so this top part by itself is identifying per table three ten fifteen V sixteen that a three gauge wire is rated 115 amps and it can carry one hundred and fifteen amps continuously however three 10.15 B the second example right here this B a three 10.15 B example there are conditions where you would correct the temperature and you might even adjust the temperature and let's assume that I had a wire rate at 90 degrees C I go to the table rated 115 amps I have to correct it for temperature I have to adjust it for conductive bundling and now I have an 80 amp wire so the impassive a conductor its ability to carry current continuously under the condition of use go back to the graphic three wires in a Raceway 86 degrees Fahrenheit its 159 wire okay five wires in a Raceway at an MP temperature 115 degrees Fahrenheit well then that's going to be an ATM wire and that's all that we're talking about let's take a look at this table right here this is Table three ten fifteen be sixteen whenever we're working conductors we will be using the 90 degrees C and pass 'ti for the purpose of this class and our books because that's the wire that we're using in solar solar guys use a lot of our HHH they use a lot of our hw2 they also use USC - - - a lot of underground single conductors B USC - 2 X h HW - - is also a wiring method so we'll get back to that so here's an example and here's the rule you see if you have wires on a roof or you bundle conductors well then we had to adjust the IMP acity right well but this part might be adjusted because it's in the roof of let's say but the side it's not in the roof well that Adam pasty is different because I don't have to let's say correct it because of temperature so you have one M pastor here on the roof and then you have a different end passively they say that's not on the roof well let's assume that the in passing in the roof is going to be 17 point 4 amps because of some type of Correction but let's say the ampacity that's not in the roof it's 30 amps well now we have a wire that has two different and passes and here's what the rule says where more than one ampacity applies to a single conductor length the lower ampacity will be used for the entire circuit so in this example here if I have a 17 point 4 amp wire on the roof and then it turns into a 30 amp wire because it's not on the Sun on the side I have to use the 17.4 amp wire as the basis that's the basic rule now there's an exception to the rule that exception says that you can actually use the higher end passing because it's an exception to the lower impassive so if this wire here is rated 55 amps but after you adjusted it or you corrected it it was rated only 31 amps you could have the entire circuit rated 55 amps if you comply with the exception the exception says this this lower ampacity cannot be longer than 10 feet and it can't be more than 10 I'm sorry it cannot be longer than 10 feet is the exception and also it cannot be longer than 10% of the length of the high ramp acity so the higher ampacity is 55 feet okay so if you want this lower and pasty to be forgotten you can't have it more than 10 feet long but it can't be more than 10% of the 55 feet so it could not be more than 5.5 feet since this is 5 foot well then it's less than the 10% of the length of the hiring faculty then I can ignore that lower opacity what what that's looking to do is saying look you run a circuit and you're just making a small stub like an AC compressor on the roof and you know 90% of the wire is inside the building at a higher ampacity you've got just a small section up on the roof at the lower rep acity don't worry about the lowering pass as long as the lauren passes i'm 110 percent of the length of the entire circuit of the higher in facet ii and it's on 1 to 10 feet long so that's a pretty handy little rule there so let's go on a little further basic rule if we go to the table is that the table is based upon 86 degrees Fahrenheit no more than three conductors that are current carrying if the temperature goes above the 86 degrees Fahrenheit or it's below 78 degrees then the ampacity that's listed on the table will be changed if you start bundling conductors now you have a problem because you have heat that can't be dissipated then you have to decrease the conductor and pasty because of the abundant effects all I'm trying to do right now is to get you to understand something conductor has an impassive it's based upon the insulation rating under the condition of use when we go to the table 3 10 15 B 16 that table gives us the condition that the table is based on it's based on 86 degrees Fahrenheit and it's based upon three current-carrying conductors anytime you do something different than the table well then that and pasty is no longer the same value so we have to correct it for temperature you'll see why in a minute and then we have to correct it also for conductor bundling let's take a look at our simple little graphic right here this graphic shows four conductors in a Raceway and the ambient temperature let's just say for right now make it easy it's a hundred and fifty degrees Fahrenheit without getting into all the details yet if I was going to find out the adjust the ampacity under the condition of use is I go to the table at the ninety degrees C for ten gauge wire because thwn - - and then go back here thwn - to t8 WH - is on this column ninety degrees C ten gauge wire a rate 40 amp so that's what it is under what not more than three conductors and you can't see the temperature of 86 degrees Fahrenheit okay so now I make the adjustment I take 40 amps at 90 degrees C I correct it because of the temperature 150 degrees Fahrenheit I adjust it because of four conductors in a Raceway like whoa wait a minute now where'd you get your where'd you get your point 58 where'd you get your point eight we're going to get to that I'm just saying that if those were the numbers then you're going to see that the numbers your value of ampacity is going to go down alright so going back to the calculation that means that the ampacity under the condition of this use is eighteen point 56 amps all I'm saying is that's the calculation and this would be like something you're doing a test hey I got four ten gauge wires with this insulation and on a roof of 150 degrees Fahrenheit what is the ambassador conductor of 40 amps times 0.5 a times point a comes out to beö was at number eighteen point five six that would be the answer then we have to see how that works in the context of the rules but that's the basic requirement to get started okay now this is contained in three ten fifteen B which was added I think in the 2011 code which i think is kind of Han but it's still kind of tricky to understand it says ampacity correction by the way if you want to make a note to yourself correction means for temperature and pass the adjustment adjust it means for conductor bundling a passive correction and adjustment factors applied to the conductor and pasty based on the temperature rating of the conductor insulation in a cordial table 3 10 15 B sixteen ninety degrees C wire means that you used ninety degrees C ampacity whatever you're going to be making any adjustment any correction or and pass the adjustment okay and pass a temperature correction let's talk about that there is a specific table that says if I tell you what the temperature is in Fahrenheit is centigrade if it's going to be different than 86 degrees Fahrenheit depending upon the conductor insulation then you would have different correction factors so let's just work an example that we are in a freezer it is less than 50 degrees C well then the correction is going to be times 0.1 1.15 which means the ampacity of 109 wire is a hundred and fifteen amp wire on the neck condition Ryan I'm going to do my best to save everybody the headache that I had we're using this table we are not using this table that I had to draw draw a giant black X through because I screwed it up so many times okay so tell me do you have a smaller table tiny table is what we use big table that's nice and easy to read and jumps off the page I don't use it well what are you in this table what's a big table for the big table then we don't you are yeah when you look at the ampacity table yoga tree 10.15 be 16 you know that's based on 86 degrees like right talking about some of the other ampacity tables are based on 104 whatever it is 104 degrees else for type Z conductors and type pfh and TFE and nickel coated and also all the whatever all it is all the medium voltage stuff all the stuff whatever three likes nobody what you're saying is Mike in the scope of the work that I do I know that table does not apply to me right now I say don't apply to somebody else right but because I don't apply it I don't want to make a mistake and going through the wrong correction factor especially for taking a test right I can see that all right let's go back here so table 3 10 15 b2 a gives us the correction factor for temperature when it's not 86 degrees Fahrenheit let's look at example here if it's 86 degrees Fahrenheit and I had 12-gauge wire if I go to Table three 1015 B 16 12-gauge wire is rated 30 amps at 9 degrees C okay I don't I because eighty six threes Fahrenheit I don't correct it so it's what it's 30 amp wire so if I asked you a question what is the empathy of 12 th HN and an ambient temperature 86 degrees Fahrenheit and three conductors in a Raceway you better answer 30 amps you better not say 20 because that's not the Ambassador if I change the question say at an ambient temperature of 50 degrees C well 50 degrees I'm sorry 50 degrees Fahrenheit if I give you 50 degrees Fahrenheit well that's colder than 86 degrees Fahrenheit which means that the ampacity is going to be adjusted for the use right foot the impasse is according to the condition of use to condition to use that it's colder the impasse is going to be greater let's go to this graphic here at 50 degrees Fahrenheit we have a correction factor 1.15 there is right there that means the amp acity is 34.5 amps so if I say what is the impasse vo 12 th HN three conductors in a Raceway at an ambient temperature 50 degrees Fahrenheit you'd better say thirty four point five amps I might change it say okay what about if I have three twelve gauge wires th H and three conductors I gave three conduction Raceway and the ambient temperature is on the roof and it's going to be a hundred and fifty degrees Fahrenheit take a look at the graphic well I'd have to go to this tape one I have to go all the way down to 150 degrees Fahrenheit and that would give me a multiplier point 58 which means I take the ampacity at 90 degrees C which is 30 amperes it should be a 30 what an a rather and that should be 30 amps times point 58 and that's going to give me seventeen point four amp wire so if I ask you what is the amp acity of twelve th hm three conductors and Raceway at ambient temperature of a hundred and fifty degrees Fahrenheit you need to say 17.4 m/s that's how we work with now you don't get into wire sizing we never get into the side you can't say something while you can put a smaller wire no all I'm saying is this is the wire and all the examples I've been using is I'm giving you the wire and I'm telling you this is the insulation I'm giving you the condition of use and I'm asking you for the ampacity don't misunderstand what I'm doing here I'm not saying how do you size a wire to a circuit that we cover back in 210 for branch circles we cover back in to 15 for feet if we get that in to 30 for services we use that to find a size conductor and then we go to 3 10 15 B to find out well what's the empaths Li under the condition of use so don't misunderstand them let's move on now to ampacity adjustment which is the bundle adjustment where for more current-carrying conductors power conductors are in a race where cable are bundled for length longer than 24 inches the impassive each conductor must be reduced per table 3 10 15 B 3a all right they're saying is this you get three wires in a Raceway no one pass the adjustment now you start getting four more guess what happens you have the surface area which is the only way you can get the heat out of that mass you have a lot less surface area relative to the mass and so therefore because of that we have to adjust the ampacity per table 3 10 15 B 3 a this has to do with how many conductors I probably should change this I need to make another this is the number of current-carrying conductors oh okay it's a number of conductors with a note number one I really don't want to go there but I'm gonna let ride take me in a second Thanks not yet but I'm gonna go we're gonna get to when we get ready to go to it number of conductors and then we'll get details later on if there's four to six conductors then the multiple I'm sorry then the adjustment is 80% then if it's seven the nine is 70% and and what have you so there's a note Ryan you know Timmy it's so easy you know the number of wires generating heat it shouldn't be a complicated thing and if you get four wires generating Heat they can't dissipate the heat you got the adjustment factor please write to me it's gonna be that easy go ahead and try it but I don't want you give me any kind of technical code stuff that don't allow on Eric answer this thing here I want you to answer that thing go ahead all right so the number of conductors I made a couple of changes because the question is okay I've got three three I'm sorry to fold boats black red white black red white okay but I'm only going to use three of those circuit conductors the other ones are spare there for future okay so how many conductors is that well that's eight but I'm only going to use some of them so which ones do I count and it got weird so what they did is is they said listen those spare conductors you count them they're not carrying current right now the assumption is they're going to tomorrow so does that mean you're going to go back in when you hook up that one wire you're going to recalculate the whole circuit of the entire length and repol all the wires no you're going to count it right now assuming that you're going to hook it up eventually so that's why it's not number of current-carrying conductors but says the number of conductors yeah I don't it's subtle and then it also gives the other note that it doesn't include conductors that can't be energized at the same time so the question is if I've got a set of 3-way switches I've got the two travelers that go between them if I turn one switch on you know one's always energized if I turn it off the other ones energized but they're never energized at the same time so I don't have to count them both because they're a fact right no matter what you do they're not both going to be on at the same time so you're only gonna count one of them all righty perfect all right let's take a look at an example right here there we go I have some source circuit conductors and let's assume I ran 12 gauge wire and it contains I guess I need to change eisah rod are you saying I need to change all my graphics in 310 and not call them current-carrying conductors here well I think it's do you think what I I think it's a useful tool to understand you don't count the equipment ground we're going to figure that out we're going to talk about it if you just say the number Y ere's well there's a green wire I got so we're gonna go with current-carrying because that I'm gonna condone seems to be what it needs to be for the purposes of despair conductors right but for what we're going to be working is we're going to use talk about current-carrying alright here we go if the raceway contains four current-carrying conductors let me go back to table 4 current-carrying conductors it's an 80% adjustment when that adjustment factor is 0.8 or 80% I go - 12 th WN - - 12 th T oh is it th n oh here th WM sir th w - 2 12 is going to be 30 amps th w maybe was th w I'm not sure if this a th w no the tables missing it that's 30 amps and then I adjust it by 80% and that's 24 m bar that's what it is my saying gave work or not I'm just saying that's the impact understand something we'll do these exercise we're not saying that wire is gonna work we just simply think that's the M passing the wire I mean this is just a calculation it's not a code resizing now there's a note here that says that the impasse the adjustment not temperature but the opacity adjustment for bundling does not apply in a Raceway having a length not exceeding 24 inches nipple the heat of the conductor bundling there's enough mass outside that's going to take care of the heat inside the Raceway it doesn't become a problem at all now let's talk about having raceways or wiring methods rather that's exposed to sunlight on the rooftop temperature values contained in table 3 10 15 B 3 C are added to the average outdoor ambient temperature now there's an exception that what we're going to talk about does not apply to X h HW - okay we're going to talk about it if it's not x h HW - - if it is i want to do the example both ways here we go this table says and by the way in your codebook there's an error in the code book because the code book should say above 1/2 inch to 3 & a half inches and there's a typo error in your code book it just says above 1/2 inch so just be aware of that mistake in your codebook so if you have a Raceway on top of a roof or a cable on top of a roof which means basically any wiring math or any race where cable depending upon the height above the roof determines how much I'm gonna focus on Fahrenheit how much additional temperature you add to the ambient temperature I'll remember this 86 degrees Fahrenheit you go to the tape when it gives you an M pass it let's just make it easy let's say those 100 amp wire on the table at 86 degrees Fahrenheit well if you put the wire on top of the roof well the roof says we have to add the the temperature that has been shown to be an adder because it's up on the roof so that is it been done and they come up with these values inside here let's assume you put it's a PV system you're putting it up on the roof and you're pretty much going to be like within let's say you're within an inch of the roof okay let me see I have an example here here we go let's go with this stamp right here and the raceway is 3/4 inches above the roof well if it with 3/4 inches above the roof I'm going to add 40 degrees to the to the ambient temperature let's say the ambient temperature is ninety degrees Fahrenheit Mike what do you get ambient temperature well there's an information to know about an Astra standard they come up with the ambient temperature it's real simple the copper guys have been look at this table here the copper guys did this table and because they did this table if you add temperature to ambient temperature then that means your temperature correction factor is going to be more severe which means you're going to have to have more copper okay that's just the way it works out so now if you go to copper dot-org and probably under electrical and under building you'll see that there's a PDF that you can download right on copper org that gives you all the ambient temperatures throughout all the major cities throughout the entire United States so if you go and you go to table pretty much it goes between about 87 till about 94 degrees surprisingly is it's not much higher than 94 and it really isn't much lower you can say well wait a minute I don't know no ambient temperature isn't like look at the temperature but no no no it isn't what the temperature is at this instant it isn't what the temperature is in the worst possible time it ever happened there are formulas that are done that are used to create what is considered an ambient temperature and there's time well we don't know the calculation of what's involved inside here so we have that's why the information on note refers us to ASHRAE and that has then of course the easiest way to get that document for free because ASHRAE is going to be this expensive document just go to copy that org get the information give you the number so I'm using 90 degrees Fahrenheit as the average as the ambient temperature but since this raceways within three quarters of an inch it has solar exposure I have to add temperature to that and the multiplying adding at a 3/4 of an inch is going to be 40 degrees Fahrenheit plus the roof temperature of 90 ambient temperature add the 40 and 90 or so come on three where's it at is it not only just about all yours here it's 130 go to the table it says it's point 76 so therefore 8-gauge thwn - 2 is rated 55 amps but under this condition of use it's rated forty one point eight amps again this is a multiple-choice question on an exam this is not high you size a wire to that pv system or that erika no no no this is just simply if i have this wire on the disk condition this is the ampacity of this conduct of this conductor yes right you mentioned briefly that you wanted to do an example of that using x hhw conductors yeah if we had if those were x hhw - 2 then your ampacity would be 53 so it would have lost two amps instead of 14 oh because because then you know just 90 we don't add the adder right so if we look at a temperature that's not an option yeah you can't have the rooftop nonsense or the rooftop rule haha sorry about that those of us that are in the electrical trade we don't like this temperature adder at all we know there's been wires been run on roofs for by like a hundred and something years and we've never seen any wire on a roof that somehow got so hot that it melted the conductors and there's a failure and that's what we need to add the same but scientists it scientifically on a moment if you do the actual things the temperature is hotter the roof than it would have not been so I mean you can't argue about the science even though we don't like it alright I'm done with that let's talk about what is current carrying conductor x' if you have a neutral and you have a phase conductor well they both draw the same current right current goes out current goes back so both those conductors would be considered current carrying if you have a balanced 120 240 or 120 208 to neutral is not considered a current carrying conductor regardless of the balancing it's just not if you have a wise system and you're using two hots in a neutral of a three-phase system well now it's a little different story because see if you carry a hundred amps on line two in 100 amps on line three and you have a neutral and you're not going to be using see three faces if we had 100 100 and hundred that would be zero if this was a hundred and a hundred that would be zero but if this is a hundred a hundred this then does not counsel it becomes 100 amps I'm going to try to kind of show you how this works out if you have a hundred amps going out on one phase and then you have a hundred amps on the other face because the way alternate current works it kind of it goes out that way hundred amps and it goes this 100 amps so therefore what happens in neutral no current at all if it's a Y system you have 100 amps going out in that direction then 120 degrees you have on our names going in that direction and if I had another hand in the center I can't do it I'd have a hundreds going in that direction and then you have 100 amps going at 180 120 degrees out of that two of the phase conductors going the other direction and the voice imagine this you're pulling in one direction 100 pounds and then you go 120 degrees away that you pull 100 pounds what would happen will you'd be moving this direction 100 pounds right you'd be moving up but if you put a hundred pounds opposite of that what happens nobody moves it's neutral there's no neutral current wrong but take two phases look at this graphic here take two phases in the neutral conductor now you have a current going 100 amps in this direction 120 degrees that direction neutral current will go in that direction one on ramp and mathematically can prove it there's a forming right here let's take a look at it we're not going to get it to that but it's real simple neutral current on two phases of a Y system is the line well it's a line squared plus the line squared minus the line times the other line squared well 100 squared plus 1 squared minus 100 times 100 which is a hundred squared comes out to be the square root up and it ends up being 100 amps so mathematically works out and because two phases of a three-phase system with the neutral is a current-carrying conductor because it carries current so you have to use lies in Ron you made a real comment about that above this graphic here is that when we talk about conductors what really talking about current conductors that are generating Heat and the equipment grounding conductor doesn't generate heat so there'd be no reason to count that no matter how we work it all out all right let me just do a quick little review here if I can and passive conductors 3 10 15 B tells us that when you have multiple M passes on a conductor length you will always use the lowest ampacity but why would you have different end passes at one part of it could be on the roof party could be bundling I mean part of it is outside the Raceway some of it inside the Ray it doesn't really matter why you have different m passes but you will use the lower and passive for the entire circuit but is that 3 10.15 a 2 exception it that says okay if you have a short section of conductor that you had to adjust for whatever reason we don't care why you made the adjustment but you change the ampacity but it's not more than 10 feet long and it doesn't exceed 10 percent of the length of the higher ampacity you know what don't worry about that little section at the end there go with the higher ampacity now and pass C is article 1 hundred under the condition of use continuous loading so you can always run continuously on a conductor that's never a problem but the ampacity is based upon the condition of use you elevate the ambient temperature then the ampacity at ninety degree C in the table can't be that ampacity because it was based on 86 degrees Fahrenheit you dropped the ambient temperature well that M Pass is no longer valid because it's not 86 degrees Fahrenheit it was based on three conductors on that table three 10 15 B 16 you have more than three conductors that's going to be generating heat and we talked about that in general well then you'd have to apply the adjustment factors three ten fifteen B three a depending upon the conductor bundling now the conductor bundling rule doesn't apply to a nipple because the heat can be able to be dissipated but if it's a nipple and it's an elevated ambient temperature you still have to correct the temperature because the ambient temperature is still the ambient temperature you might have a condition very common for solar installations where you would have up solar exposure so you have to then add the adder on top of the rooftop exposure so you have correction factors you might be bundling a lot of these source circuit conductors together well then you're going to have to adjust up some passes of all these conductors that are bundling and then you make the adjustment after all of that that gives you the ampacity conductor now we've already covered two 40.4 and it said this conductors must be protected at the ramp acity we've now learned there's a lot of reasons why the impasse t will not be the ampacity in the table but whatever you do when you get done with it two-forty that for says conductors must be protected in accordance with the ramp acity but then 244 be seized if the ampacity doesn't correspond at a standard size and you can use the next standard size as long as that circuit is not supplying receptacles because you have no way to control receptacle loads so after we do all these calculations we going to have to do one more thing your basic rule conductor sizing I think it's 210 I guess that's 19 a1 tells us your sizing conductor at 125 percent of the continuous load is that right Brian and then in feeders it's 2 15.3 a take a look at that how do you sighs if you without at 300k to 15.2 oh yeah a 1 a 1 says you sized to conduct 125 percent of the continuous load okay so now I take mine continues load at 125 percent I add the non continuous load now what's the maximum non continuous loads you can put it on a 20 amp circuit 20 amps so if I have a 20 amp could non continuous load what sighs why do I need while I need 20 F wire so that you need 20 F wire you size it based upon the terminals you have to go to Table three ten fifteen complying with 110 that 14 c1 rules betting upon whether it's over hundred amps 100 amps you size the wire same well I take one hundred twenty five percent of the continuous load I take the non continues load add that together go to the terminal ratings as per once and 14 it says I need to have a three gage wired I'm like yeah but how many wires are you running in that race way what's the ambient temperature oh I'm on the roof oh I have four conductors you correct it and you adjust it now you got to find out well what size breakage you had well I had a hunter amp breaker and I had a hunter ramp wire but now I had to adjust and correct the wire that wire is only rated 88 amps okay even though that the wire size that you selected is fine for mass four terminals for those other rules because of the adjustment in the correction required and you adjust at the ampacity based upon the 90 degrees see that wire cannot be protected according with two 40.4 so we're slowly starting to put together the pieces and I apologize it is complicated but this is what your job is you're the professional this is not something we can just dismiss the somebody else you can say well Eric and Victor the engineers are supposed to do that I don't think so I mean yes they're supposed to do that but when I was electrician I could tell you one thing I calculated voltage drop of every single circuit I calculate the conductor size in the protection when I got a set of blueprints because I wanted to pry some practice and practice and practice I wanted to make sure you know what we're working together as a team same thing with the inspector we're coming out to make sure that when we leave that job we help the engineer the inspector helped the contractor the contractor worked with the owner we all are working together to make sure it's safe so please don't take all this stuff it's like dismissive we need leaders we got a bunch of people watching this videotape streaming live and you guys are really are motivated you're the leaders you're watching this DVD I want to help you all of us guess what Ron Jackson's going to be gone I'm going to be gone Victor all of us are going to be gone someday we need you guys to take the information that we're trying to consolidate we're trying to give we're trying to pass on to the next generation we want you to make sure you make the installation safe do you know what I think it should be reasonable that you should be able to figure out how to size the wire in a breaker to a circuit you have ambient temperatures yep temperature bundling and factors inside here yep terminals consideration you have continuous load you have insulation ready I understand it's not easy well that's okay it's not supposed to be easy I mean this is a very complicated industry and we just need to make sure that we take the time and that we do it let's go to dwelling unit feeder and service conductor sizing now this only applies to dwelling units feeder and service conductor sizing and here's what the code rule says that when it's feeder and service conductor sizing you're going to comply with 3 10 15 b 7 one through four so let's take a look at it one service conductor supplying the entire load of a dwelling unit 120 240 volt system can have an impasse the size at 83% of the service rating so if you take a look at this example here the service conductors supply the entire load to the service and these okay we're going stop right there and it's saying you size the service conductors to 83% of the rating of the overcurrent device so this is a 200 amp device that I need 166 amp wire table 3 10 16 B 16 will tell us that's the two gates to hotwire rated 175 we're good to go there that's your B 1 B 1 says that the 83% rule cannot be used conductors apply more than one dwelling unit C this is a one-family dwelling this is a one I can't say one family dwelling yeah it's a one-family dwelling right it sells beans your family rolling so it's a one-family dwelling this rule can only applies to a one-family dwelling right the feeder right out of the service so I'll put the heading in here this should be what one-family dwelling go back over here the service conductor 83% would apply to a dwelling unit but it does not apply to duplex now b72 talks about the feeder carrying the entire load supplied by the service 200 amp device 83% is going to be that same 166 if you have a duplex you can't use the 83% rule for the service because it's not a one-family dwelling but you can use this 83% rule for the individual dwelling unit feeders and the reason being is that the diversity of a dwelling unit really let me tell you something I've done I've done both the calculation to the service of my house is probably 300 amps the actual load to my house probably does not more draw than more than 50 amps ok so that's just the way it's going to be in probably worst case scenario maybe I could draw 60 maybe 70 amperes so when you go to 220 calculate those numbers are like so far off the chart that it's ridiculous now the 310 guys they've done something utilities a priori inside they're saying hey let's let's cut the size of these conductors let's try to keep it cost-effective in there and I guess state that 83% rule which is a change in the 2014 code because I guess that was the percentage that they used to generate those tables originally now Ryan does 83 percent is that limited to 400 amps I didn't really look at that or is that just 83 percent and so therefore if I have a 1200 amp service were dwelling in it now I can size of service conductors and feeder conductors 83% because before we had a table that table was up to four hundred amperes so how's that looking now yeah four hundred amps it says okay 120 240 up to four hundred amperes you get your over current device you get you 83 percent if it carries the entire load we're good to go yeah and I wanted to mention also your you said the eighty-three percent was the original thing and and and your so almost right it's kind of like some room right now is the other wrong you're right now was the only reason I knew you were on right I remember there was something I'm reading the proposal it was it was initially the math was done based off of 84 percent but when they made this change that this was in 1956 by the way right and then when they made this change they said no we want it to be 83 percent and the only reason I'm even bringing this up is they said 83 percent is used to maintain consistency with the sizes in the 2011 table 3 10.15 b7 so I guess the reason I'm saying this and I just realized it if you're like me and you like a nice little table that says what size wire for what size breaker we cut that baby out of your 2011 code book and just glue it on this page because I think that's what I'm gonna do oh yeah yeah see yeah I'm gonna you know I'm gonna do I'm gonna tape it over the big X team listen make your code book your code book I don't have access to you I'm sexy if I go in my cookbook here I know I'm gonna have some pages somewhere in here that I actually did that right hop to find it real quick oh here's right here here right some pages right take that baby right inside there so that way I don't sit there and try to why would you do the math every single time go to the 2011 code get the table snag it yep great print it out tape it bum going in there and by the way if you take a look at this graphic it does not apply when you have a 120 208 single phase feeder to a dwelling unit and we talked about that previously because if you have 200 amps on line one and 200 amps on line two the neutral is not zero but the neutral becomes current-carrying so this only applies to 120 240 volt single-phase feeders and sir conductors carrying the entire load supplied by the service now you got to be careful in the Ryan you're gonna have to help me here because either they move a couple rules here you ready for this I got a service I'm bringing my 83% I got a 200 amps I'm getting whatever that comes out to be in wire sighs was it like a 2 watt or something like that for a 200 amp service I think it comes out to be so I put my 200 amp to auto conductor coming into the overcurrent device but now I'm going into a panel outside a meter main panel and I'm picking up the AC and the pool pump on a couple things now I'm going to go Brian Brian I'm gonna go through my feet through lugs you're with me and I want to go to the feeder lugs and I'm going to go hit my panel inside I have a two hundred panel inside but I don't want to be running 200 amp wire inside but since I have a 200 amp overcurrent device and it says I can only use the 83% when it carries the entire load supplied by the service but I'm not taking the entire load supplied by the service but it doesn't make any sense because I'd have to run three odd wire to the inside panel inside is there a rule that says however the feeder conductors never have to be large in the size of the surface conductors and where is that yeah that's in b7 the rule that we're reading parenthetical 3 which says in no case shell a feeder for an individual dwelling unit be required to have an ampacity greater than that specified in b7 1 or 2 which is what we just talked about right okay all right so even though it has secured the entire load supplied by the service to be the 83% the thing is this your size the server is 83% go to baby 2011 code get that table stick that out there okay and that's the sighs why are you sighs - the feeder whether or not it carries the entire load supplied by the service so just be aware that I don't want you thinking you bring in 2 OTT 4 200 amp service and then have to bring in 3 ought to the feeders because it doesn't have to be larger than that

Channel: MikeHoltNEC

Views: 237,947

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Id: OLIHEiiY_Rs

Length: 42min 3sec (2523 seconds)

Published: Wed Feb 05 2014