1 00:00:33,399 --> 00:00:37,479 What's up, everybody? Welcome to another episode of Let's Ask Paul, the 2 00:00:37,560 --> 00:00:43,159 podcast where you get to ask me Paul Abernathy anything you want about the National 3 00:00:43,240 --> 00:00:48,640 Electrical Code, all things electrically related, and if selected, I will respond 4 00:00:48,840 --> 00:00:53,200 in a podcast much like today, or I could respond in an email. 5 00:00:54,200 --> 00:00:57,479 All you gotta do is again, go to Paul abernatty dot com, submit 6 00:00:57,560 --> 00:01:00,799 your information, and we will define me either way get you an answer. 7 00:01:02,560 --> 00:01:06,719 Now. I get hundreds of these, so again bear with me. We'll 8 00:01:06,719 --> 00:01:08,959 get to them as quick as we can. But I love getting them, 9 00:01:10,000 --> 00:01:12,480 so I do appreciate you folks sitting in your questions. Just do me a 10 00:01:12,480 --> 00:01:17,680 favor. Make sure you specify the code cycle that your question is based around, 11 00:01:18,079 --> 00:01:22,359 and be as very detailed and descriptive as possible, because, as you 12 00:01:22,439 --> 00:01:23,879 know, with a lot of things, there can be certain variables, and 13 00:01:23,920 --> 00:01:26,959 we don't want to make sure that we get it wrong because of a variable 14 00:01:26,959 --> 00:01:30,519 that we leave out, so we want to want to make sure that we 15 00:01:30,599 --> 00:01:33,400 do it right. So please, by all means, if you're going to 16 00:01:33,439 --> 00:01:38,560 submit something to us, make sure that you submit the details involved. Okay, 17 00:01:38,920 --> 00:01:42,760 thanks again for following me, folks and listening again. You can listen 18 00:01:42,760 --> 00:01:48,719 to these podcasts on any of your favorite listening platforms, Apple Podcasts, Google 19 00:01:48,760 --> 00:01:53,959 Podcasts, Breakers, Spotify, Deezer, our Heart Radio. 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If you're on your desktop and you go there and 30 00:02:37,479 --> 00:02:39,120 you see a bar code, a QR code, you can just scan it 31 00:02:39,159 --> 00:02:42,919 with your phone. It'll ask you do you want to load it onto your 32 00:02:42,919 --> 00:02:46,199 homepage? Answer yes, We will not load any software into your phone. 33 00:02:46,240 --> 00:02:52,439 It is simply a link to our mobile web based app and on your phone 34 00:02:52,479 --> 00:02:55,240 it works just like an app, but we update it and that way it's 35 00:02:55,280 --> 00:03:00,319 always relevant and we're always adding new things, new calculators, new resources. 36 00:03:00,960 --> 00:03:05,159 There's a chat feature you can post pictures of an install and you're like, 37 00:03:05,199 --> 00:03:08,199 hey, what do you think about this? And it's only available for the 38 00:03:08,240 --> 00:03:14,080 members who have the mobile app, So again it's very nice, a very 39 00:03:14,159 --> 00:03:16,919 knit group there that have the mobile app. Always remember, folks, you 40 00:03:16,960 --> 00:03:20,280 got to register your app though, so once you get it, you got 41 00:03:20,280 --> 00:03:23,159 it. You'll see on there about your access. You got to create your 42 00:03:23,159 --> 00:03:25,800 account on the app, so people are from forgetting to do that. But 43 00:03:25,919 --> 00:03:29,360 once you get the app, you got to register your app. So the 44 00:03:29,360 --> 00:03:31,759 instructions are right there in the app. You just click the icon. It 45 00:03:31,800 --> 00:03:37,759 talks about the registration and getting your account for the mobile app. Once you're 46 00:03:37,759 --> 00:03:39,159 set up, then you're good to go. Okay, So don't let it 47 00:03:39,199 --> 00:03:46,360 confuse you, all right. So ongoing episodes, we've did quite a few 48 00:03:46,360 --> 00:03:50,879 episodes we've been doing based on this question that was submitted to me. We 49 00:03:51,039 --> 00:03:54,800 answered about parallels, series circuits, we did combinations, we did OHMS law, 50 00:03:57,000 --> 00:04:00,159 we've done all of that. We talked about how to formulate the horsepower. 51 00:04:00,680 --> 00:04:05,560 We have different episodes that are available. They'll be titled correctly so they'd 52 00:04:05,560 --> 00:04:10,439 be easy for you to differentiate those over in whatever platform you want to listen 53 00:04:10,479 --> 00:04:15,720 to us on. Again, we're on Spreaker, a Deezer Apple podcast, 54 00:04:15,759 --> 00:04:19,639 Google podcast. I like to listen on Spotify personally, but you do whatever 55 00:04:19,680 --> 00:04:25,319 you do. And so this episode, we're going to be focusing and it's 56 00:04:25,360 --> 00:04:28,959 not gonna be a long one, but we're gonna be focusing on transformer sizing. 57 00:04:30,000 --> 00:04:36,000 And again, this is gonna be difficult to do kind of in a 58 00:04:36,040 --> 00:04:40,959 podcast, but we're going to do our best to do it and try to 59 00:04:41,000 --> 00:04:45,399 convey it what we're talking about here. Okay, So sizing a transformer. 60 00:04:45,439 --> 00:04:47,040 So we're gonna do a single phase transformer and they're gonna do a three phase 61 00:04:47,040 --> 00:04:51,319 transformer, and kind of give you some basic synopsis of how this would work, 62 00:04:51,680 --> 00:04:56,319 okay, so that you get kind of an understanding on what you may 63 00:04:56,399 --> 00:05:00,920 or may not do. Now, we'll also talk about kind of how to 64 00:05:00,040 --> 00:05:04,920 calculate the primary and secondary amps, because that is probably more in line with 65 00:05:04,959 --> 00:05:09,560 what you would get on an exam for those that are preparing for an exam. 66 00:05:09,920 --> 00:05:12,959 But I also want to start out with a more practical application of when 67 00:05:13,000 --> 00:05:17,120 you have specific loads in how you would size your transformer. So this is 68 00:05:17,439 --> 00:05:21,000 again a very practical, high level version. We're not getting into a bunch 69 00:05:21,000 --> 00:05:28,040 of extra nuanced variables. This is the basic information. And of course we 70 00:05:28,120 --> 00:05:30,759 have a video series it's available that goes deeper into transformers than this, but 71 00:05:30,800 --> 00:05:33,560 I want to kind of give you that. So I also will tell you 72 00:05:33,600 --> 00:05:39,600 that if you do have the Uglies Book, this is the versions that is 73 00:05:40,000 --> 00:05:43,040 in the Uglies Book. So I want to give credit where credit's due. 74 00:05:43,040 --> 00:05:46,000 I didn't want to reinvent the wheel. The Ugliest Book is an amazing resource 75 00:05:46,040 --> 00:05:51,720 if you've got it, but again it's not translated into easy listening. So 76 00:05:51,800 --> 00:05:57,040 that's what the episode today is trying to convey. All Right, So the 77 00:05:57,079 --> 00:06:01,399 first thing sizing a transformer a single phase transformer. So let's say we size 78 00:06:01,480 --> 00:06:05,600 a four hundred and eighty volt primary and it's going to be a two forty 79 00:06:05,639 --> 00:06:11,480 one to twenty volt secondary transformer. Okay, so for eighty primary two forty 80 00:06:11,519 --> 00:06:18,639 one twenty secondary single phase transformer. For the following single phase incandescent. I 81 00:06:18,639 --> 00:06:24,160 mean, I don't know if anybody uses incandescent anymore. But anyway, incandescent 82 00:06:24,720 --> 00:06:32,519 lighting loads consisting of forty eight recessed luminaires, each rated two ampiers. Okay, 83 00:06:33,519 --> 00:06:36,720 oh, each rated two ampiers and it's one hundred and twenty volts. 84 00:06:38,079 --> 00:06:44,480 Each fixture or luminair has one hundred and fifty watt lamp. Okay. Now, 85 00:06:45,839 --> 00:06:49,959 these luminaires can be evenly balanced on the transformer. It's a single phase 86 00:06:50,000 --> 00:06:54,879 transformer. But you know what, we do not use the lamp wattage here, 87 00:06:55,240 --> 00:06:58,720 because that's the first thing I want to convey. We're trying to calculate 88 00:06:58,800 --> 00:07:00,839 and we're trying to get the VA value. We're not going to be using 89 00:07:00,879 --> 00:07:05,040 the wattage. Okay. First thing we want to make it clear. Now, 90 00:07:05,079 --> 00:07:10,560 what we got in the question is that each one of these are two 91 00:07:10,720 --> 00:07:15,160 ampiers each, okay, and here's forty eight of them. Okay. So 92 00:07:15,279 --> 00:07:17,199 what we want to do is we want to find out what the VA is 93 00:07:17,360 --> 00:07:20,160 for each one of these based on the amps, based on the vaults. 94 00:07:20,319 --> 00:07:25,040 Okay. That's why it's so important for you to understand Ohm's law, right, 95 00:07:25,439 --> 00:07:28,839 And hopefully you went back and listened to that podcast I did on Ohlms 96 00:07:28,920 --> 00:07:32,839 law, because this is straightforward, If every one of these luminais are two 97 00:07:32,920 --> 00:07:39,279 ampiers times one hundred and twenty volts, okay, so again two times one 98 00:07:39,439 --> 00:07:45,040 twenty and that is two hundred and forty vault ampiers or va. And how 99 00:07:45,079 --> 00:07:47,519 many did we have. We had forty eight of these things, okay, 100 00:07:48,319 --> 00:07:56,639 So two forty times forty eight that equals eleven five hundred and twenty va. 101 00:07:56,800 --> 00:08:03,199 So that is what our lighting contribution is on this transformer. Okay, this 102 00:08:03,319 --> 00:08:09,319 single phase transformer the secondary pay. So in that scenario, we now want 103 00:08:09,319 --> 00:08:15,199 to get that into kVA. Well, obviously we know eleven five hundred and 104 00:08:15,240 --> 00:08:20,120 twenty is va. That in order to do to get this into kVA, 105 00:08:20,319 --> 00:08:22,279 we just simply divide that by thousand, okay, So I'm gonna divide that 106 00:08:22,279 --> 00:08:28,720 by thousand, and that as eleven point five to two kVA. So when 107 00:08:28,759 --> 00:08:33,960 you go looking at single phase transformers and I need to find one that is 108 00:08:35,000 --> 00:08:39,320 at least eleven point five to two kVA, well, chances are the one 109 00:08:39,360 --> 00:08:41,879 the next one you're going to find larger than that is going to be a 110 00:08:41,000 --> 00:08:48,960 fifteen kVA transformer. Okay, So that's what you would have. So keeping 111 00:08:48,159 --> 00:08:52,720 keeping that in mind, that's exactly how you would do it. Now, 112 00:08:52,879 --> 00:08:58,240 it should go without saying that when you actually physically do this in the panel, 113 00:08:58,399 --> 00:09:01,840 the distribution or balance it making sure you're evenly balancing on each phase of 114 00:09:01,840 --> 00:09:05,080 this transformer. Because it is to forty volt one twenty, so you have 115 00:09:05,120 --> 00:09:09,279 two legs that are one twenty, so you want to balance them out. 116 00:09:09,480 --> 00:09:13,440 So that means that in this case we had forty eight luminaires, I'm going 117 00:09:13,519 --> 00:09:16,240 to put twenty four on Leg A and it's single phase, so we'll just 118 00:09:16,279 --> 00:09:20,559 say Leg A and we'll do twenty four on Leg B. So again we're 119 00:09:20,559 --> 00:09:26,600 going to evenly distribute these loads on the between the different phases, and of 120 00:09:26,639 --> 00:09:30,399 course then that means the neutral is going to see what the imbalance, which 121 00:09:30,399 --> 00:09:33,639 in this case is nothing right for these these are going to be balanced out 122 00:09:33,840 --> 00:09:39,279 for this single phase transformer. Now, one thing to remember that kVA, 123 00:09:39,759 --> 00:09:43,720 whatever the primary is, is also the secondary. So I mean, if 124 00:09:43,720 --> 00:09:46,559 it's fifteen kvas, which you choose, and it's fifteen kVA across the board, 125 00:09:46,840 --> 00:09:50,879 okay, whether it's primary secondary, it's a fifteen kVA transformer, it 126 00:09:52,000 --> 00:09:54,799 just so happens that the load we're dealing with is going to be placed on 127 00:09:54,840 --> 00:09:58,200 the secondary. But we calculate it out at the fifteen kVA and that's the 128 00:09:58,240 --> 00:10:03,679 transformer mi of them that we would need. Okay. Now moving on to 129 00:10:03,759 --> 00:10:07,919 this equation where it would be a three phase transformer, then we're going to 130 00:10:09,000 --> 00:10:13,679 incorporate some three phase loads here, So sizing this transformer for these loads, 131 00:10:13,679 --> 00:10:16,440 and again remember these loads are on the secondary. That's the whole point is 132 00:10:16,440 --> 00:10:20,840 we're picking up these loads, that is taking it from like in our single 133 00:10:20,840 --> 00:10:24,480 phase four eighty volts, we're dropping it down because we need one to twenty 134 00:10:24,559 --> 00:10:28,480 volt loads to handle or lighting loads that we had. So in the three 135 00:10:28,519 --> 00:10:33,879 phase, if you had a primary of four hunder and eighty volts and you 136 00:10:33,960 --> 00:10:39,159 had a secondary of two hundred and forty volts. Again, three phase transformer, 137 00:10:39,240 --> 00:10:46,039 which is again a polyphase transformer, it says to supply one three phase 138 00:10:46,240 --> 00:10:50,200 twenty five kVA process heater. Okay, so it's going to be using all 139 00:10:50,200 --> 00:10:54,840 the legs in a three phase, but then it has a one single phase 140 00:10:54,440 --> 00:11:00,720 five kW unit heater. Now it's not going to be something that you can 141 00:11:00,879 --> 00:11:05,120 balance that five kW amongst the other phases because it's only using one phase. 142 00:11:05,840 --> 00:11:09,639 So there's no way you're going to be balanced to be able to balance out 143 00:11:09,639 --> 00:11:13,720 this transformer. So what do we typically do with that? Since that five 144 00:11:13,840 --> 00:11:18,960 kW is only going to be on one phase, it adds loads directly, 145 00:11:18,480 --> 00:11:22,360 and if you were to do it that way, you run the risk of 146 00:11:22,480 --> 00:11:28,480 undersizing your transformer. So it is very common practice to even though it's only 147 00:11:28,559 --> 00:11:31,600 five kW on the one leg or the one phase, you really want to 148 00:11:31,600 --> 00:11:37,879 do it times three, so it's like the five kW on each phase in 149 00:11:37,960 --> 00:11:41,399 order to balance it out. Okay, that's very common practice. Whether you 150 00:11:41,440 --> 00:11:43,320 do this or not, that's just a very common practice. So it'd be 151 00:11:43,399 --> 00:11:48,240 five kW times three would be fifteen, and then you have the original twenty 152 00:11:48,320 --> 00:11:54,559 five kVA which is for the three phase right, so it'd be twenty five 153 00:11:54,639 --> 00:11:58,840 plus fifteen, which comes up to be a total of forty kVA. And 154 00:12:00,000 --> 00:12:03,840 of course, at that point, if you go look at your transformer three 155 00:12:03,879 --> 00:12:09,519 phase transformers, probably the next side that meets it or exceeds that forty kVA 156 00:12:09,720 --> 00:12:16,200 would be a forty five kVA transformer. That makes sense, Okay, that's 157 00:12:16,200 --> 00:12:20,200 probably what you're going to do. Pretty much in the field, that type 158 00:12:20,200 --> 00:12:24,799 of thing we don't want to run the risk of undersizing our transformer, okay, 159 00:12:24,559 --> 00:12:30,039 all right. So the next thing is, okay, so what if 160 00:12:30,080 --> 00:12:35,639 we know the transformers kVA and remember it's fifty kVA whether it's primary or secondary. 161 00:12:35,759 --> 00:12:37,759 That you know the old saying wats in wat's out. Watts is watts 162 00:12:37,759 --> 00:12:45,320 whether it's primary secondary, watts equates to what also the va. Okay, 163 00:12:45,879 --> 00:12:50,720 So if it's kVA, it'd be the same as killowatts. If it's VA, 164 00:12:50,879 --> 00:12:52,960 is the same as watts, So they're synonymous here, okay. So 165 00:12:54,039 --> 00:12:56,679 let's kind of work this out. So what if we have a transformer now, 166 00:12:56,360 --> 00:13:01,039 and we want to work out the amps on primary side, and we 167 00:13:01,080 --> 00:13:05,440 want to work out the amps on the secondary side. Okay. So let's 168 00:13:05,440 --> 00:13:11,799 say we have a four to eighty two forty volt single phase fifty CAVA transformer 169 00:13:11,919 --> 00:13:16,679 with a total Z impedance of two percent, which is marked on the side 170 00:13:16,720 --> 00:13:22,720 of the transformer, okay, and that's what's being installed. It's not a 171 00:13:22,799 --> 00:13:26,679 very efficient transformer, but it's two percent impedance, okay, which is the 172 00:13:26,759 --> 00:13:31,120 Z all right, And so it's being installed. So we need to calculate 173 00:13:31,159 --> 00:13:39,519 the primary and secondary amps and we can even calculate the short circuit current at 174 00:13:39,519 --> 00:13:43,240 this transformer. Yes, we can, all right, so let's do it. 175 00:13:43,279 --> 00:13:48,039 So what's the formula? So to find the total current on the primary 176 00:13:48,080 --> 00:13:50,919 which is the I for current in P. That's usually what you have, 177 00:13:50,960 --> 00:13:54,360 an I and then a little P that's the primary current. The formula is 178 00:13:54,480 --> 00:13:58,600 Cavea times one thousand, and we really don't need to do that if you 179 00:13:58,600 --> 00:14:01,960 already know that it's fifty kVA. You know the K is one thousand, 180 00:14:01,960 --> 00:14:07,240 so you know it's fifty thousand. But anyway, to stay consistent, we'll 181 00:14:07,240 --> 00:14:11,240 do kVA, which is fifty times a thousand, and if you've heard me 182 00:14:11,279 --> 00:14:15,240 tell you before, in this formula, the top portion is the numerator, 183 00:14:15,279 --> 00:14:18,480 the bottom portion is the denominator. Only reason I'm doing it this way is 184 00:14:18,559 --> 00:14:22,799 to pink this mental picture. It's kind of like a fraction. You know 185 00:14:22,840 --> 00:14:24,399 what goes on the top and you know what goes on the bottom, right, 186 00:14:24,480 --> 00:14:28,519 So that's kind of why I do this. So the top part is 187 00:14:28,559 --> 00:14:33,799 going to be fifty thousand, and then the bottom part is the E primary, 188 00:14:33,840 --> 00:14:37,360 which E is the voltage and P being the primary voltage. So this 189 00:14:37,399 --> 00:14:43,120 would be four under and eighty volts, right, that's the primary, So 190 00:14:43,720 --> 00:14:48,279 fifty thousand at that point you're saying, okay, that's the primary voltage. 191 00:14:48,320 --> 00:14:54,000 But what we're going to do is we're do fifty thousand divided by or numerator 192 00:14:54,039 --> 00:15:00,039 divided into the denominator, which is for eighty. Because the voltage for the 193 00:15:00,000 --> 00:15:03,799 the primary is four eighty, so that would be fifty thousand divided by four 194 00:15:03,879 --> 00:15:07,879 eighty and that is gonna give me one hundred and four point one six. 195 00:15:09,200 --> 00:15:11,840 And you know we can drop anything that is under point five, so we're 196 00:15:11,919 --> 00:15:16,799 dropping it. So that as one hundred and four amp years on the primary 197 00:15:16,879 --> 00:15:22,679 side for this transformer at that impedance at two percent impedance. Okay, that's 198 00:15:22,720 --> 00:15:26,200 what we've got. Now the impedance really doesn't come into play yet. That's 199 00:15:26,240 --> 00:15:31,080 only gonna be when we do the short circuit. But anyway, just throw 200 00:15:31,120 --> 00:15:33,279 it in there so you understand that's what that transformer is based on. Now 201 00:15:33,320 --> 00:15:39,399 doing the secondary, remember the numerator, the top part doesn't change, the 202 00:15:39,519 --> 00:15:43,480 KVEA doesn't change. It's the same whether it's primary secondary. Don't get lost 203 00:15:43,480 --> 00:15:48,000 in that. So it's still fifty thousand. The only difference here is the 204 00:15:48,240 --> 00:15:56,320 secondary voltage is two forty, right, So we're gonna do fifty thousand, 205 00:15:56,799 --> 00:16:02,360 okay, and we're gonna do fifty thousand and divided by two forty, and 206 00:16:02,399 --> 00:16:04,360 that gives me two hundred and eight point three. Drop the point three, 207 00:16:04,480 --> 00:16:08,879 so it's two hundred and eight for the secondary. So this transformer, this 208 00:16:08,960 --> 00:16:17,720 fifty kVA transformer, has a primary amperage rating of one oh four in a 209 00:16:17,879 --> 00:16:22,600 secondary amperage rating of two zero eight. Okay. Now we want to know 210 00:16:23,279 --> 00:16:30,120 what is the short circuit current rating that we're dealing with here, Okay. 211 00:16:30,360 --> 00:16:33,120 So in order to do that formula, you simply and again we're using the 212 00:16:33,159 --> 00:16:37,519 secondary because that's where our loads is. That's where we're going to be dealing 213 00:16:37,559 --> 00:16:40,320 with, you know, with with with everything that's going to be connected on 214 00:16:40,399 --> 00:16:44,159 the load side of it, okay, or the secondary side. So the 215 00:16:44,200 --> 00:16:48,879 short circuit ampires for that secondary, and that's referred to as the is s 216 00:16:48,039 --> 00:16:55,639 C. Okay, is the in the formula is the current from the secondary 217 00:16:55,679 --> 00:17:02,200 divided by the impedance that's given to us in the equation in this case was 218 00:17:02,240 --> 00:17:06,559 two percent. So how do you remember what we always do with percentages? 219 00:17:06,599 --> 00:17:08,680 We want to get it down to decimals. Start at the right and move 220 00:17:08,680 --> 00:17:14,000 two spaces to the left, so two percent becomes start from the right, 221 00:17:14,079 --> 00:17:17,240 move it two spaces to the left, it becomes point zero two. Correct. 222 00:17:18,200 --> 00:17:22,559 So now it's a simple equation to find the short circuit ampurating. Okay, 223 00:17:22,079 --> 00:17:27,000 right here at the secondary is two toh eight. Okay, that's the 224 00:17:27,039 --> 00:17:32,480 amps that was from the secondary. We already calculated that divided by point zero 225 00:17:32,519 --> 00:17:37,720 two and that is ten thy four hundred ampiers. And so that is what 226 00:17:37,759 --> 00:17:44,400 your short circuit ampiers are. Okay, right there at that secondary. All 227 00:17:44,480 --> 00:17:48,599 right, Now there is apps out there just to throw this out there. 228 00:17:48,720 --> 00:17:52,279 Cooper Bustsman has a great app that will really, you know, work all 229 00:17:52,319 --> 00:17:56,920 this math for you and all that as you continue down. But again, 230 00:17:56,200 --> 00:18:03,000 that is basically how we would do it for a single phase transformer. Okay, 231 00:18:03,920 --> 00:18:07,960 Now what about a three phase Okay, let's look at this differently with 232 00:18:07,000 --> 00:18:11,160 a three phase. Now, like always, since we're dealing with three phase, 233 00:18:11,200 --> 00:18:12,839 we're gonna be bringing in the square root of three, which is one 234 00:18:12,839 --> 00:18:17,240 point seventy three to two. But I'm gonna remind you if you want to 235 00:18:17,359 --> 00:18:23,839 use simply one point seventy three in your equations. You are perfectly okay to 236 00:18:23,920 --> 00:18:27,440 do that. It's gonna work out the same, and it's not gonna be 237 00:18:27,559 --> 00:18:30,680 enough variable when you start doing the roundings that it's gonna make a difference. 238 00:18:32,039 --> 00:18:36,799 But you do you, and I'm gonna use one point seven to three today. 239 00:18:36,839 --> 00:18:40,200 But remember square root of three is actually one point seven three two. 240 00:18:40,240 --> 00:18:41,720 You want to use the whole value. That is perfectly fine to you. 241 00:18:41,839 --> 00:18:45,240 It's not gonna make a difference in the equation. And if you don't believe 242 00:18:45,279 --> 00:18:48,960 me, work it out, you'll see it's not gonna make a difference, 243 00:18:48,319 --> 00:18:51,599 bait, once you do all your rounding and everything you're supposed to do. 244 00:18:52,119 --> 00:18:53,480 All right, So let me give you the next the next one here, 245 00:18:53,559 --> 00:18:57,799 So we need to size and find out what the primary and secondary amverage current 246 00:18:57,960 --> 00:19:04,480 is for a three phase transformer. So it's a four eighty two oh eight 247 00:19:04,599 --> 00:19:11,519 vote three phase transformer. It's one hundred kVA transformer, and its impedance is 248 00:19:11,599 --> 00:19:17,240 one percent, okay, and it's being installed. So if this is the 249 00:19:17,319 --> 00:19:19,519 kind of question that you get on an exam, it's basically just wanting you 250 00:19:19,559 --> 00:19:26,240 to determine what the primary amps and what the The secondary amps are pretty easy 251 00:19:26,240 --> 00:19:30,400 and straightforward. It's simply the same as it was before for the single phase. 252 00:19:30,880 --> 00:19:36,039 The only difference is in the denominator portion the bottom. You're going to 253 00:19:36,079 --> 00:19:38,559 be adding the one point seven three or one point seventy three to two if 254 00:19:38,599 --> 00:19:42,039 you desire, in order to come up with the lower portion. Okay, 255 00:19:42,519 --> 00:19:47,240 So let's kind of work this one out. So I think we all know 256 00:19:47,920 --> 00:19:52,519 that one hundred kVA. Think of the k as a thousand, So this 257 00:19:52,599 --> 00:19:56,119 is one hundred thousand va, and that goes in the top portion, which 258 00:19:56,160 --> 00:20:03,319 is the numerator, and then the bottom portion was for eighty okay, for 259 00:20:03,519 --> 00:20:10,559 eighty times one point seventy three two, and that would give you up four 260 00:20:10,599 --> 00:20:15,400 eighty times that Goness calculator for eighty times one point seventy three two. If 261 00:20:15,400 --> 00:20:18,920 that's what you're using, that's going to give you eight thirty one point three 262 00:20:19,079 --> 00:20:22,160 six. You're more than happy to drop the point three six and use one. 263 00:20:22,480 --> 00:20:26,519 I just use eight thirty one. It's going to be fine. If 264 00:20:26,519 --> 00:20:29,799 you want to use the whole amount, that's fine. Two. I'll do 265 00:20:29,880 --> 00:20:34,279 both if you want. Now, if I do this same thing for eighty 266 00:20:34,319 --> 00:20:42,119 times one point seventy three. You'll see that the value is eight thirty point 267 00:20:42,160 --> 00:20:47,799 four, okay, which again you wouldn't round up, so you'd be using 268 00:20:47,799 --> 00:20:48,799 eight thirty. At the end of the day, you're going to see that 269 00:20:48,839 --> 00:20:52,880 it's not going to make a big difference in the load. I'll show you, 270 00:20:52,359 --> 00:20:55,960 all right, So let's use the first one. Well, we did 271 00:20:55,960 --> 00:21:00,880 the whole amount of the four eighty times. It is one point sevent three 272 00:21:00,920 --> 00:21:06,680 two. So again four eighty times one point seven three two was eight thirty 273 00:21:06,720 --> 00:21:11,319 one thirty six. So we're gonna do one hundred thousand, okay, divided 274 00:21:11,359 --> 00:21:15,640 by eight thirty one point thirty six, and that gives me one hundred and 275 00:21:15,720 --> 00:21:18,200 twenty point two eight. We dropped the point two eight, so it's one 276 00:21:18,279 --> 00:21:25,079 hundred and twenty ampiers. That is the primary current. Okay. Now, 277 00:21:25,119 --> 00:21:30,640 just to show you it's no different, I'll do the four eighty times one 278 00:21:30,640 --> 00:21:33,759 point seven three instead, and that's eight thirty point four. So I'll do 279 00:21:33,839 --> 00:21:41,079 one hundred thousand divided by eight thirty point four, and as one hundred and 280 00:21:41,079 --> 00:21:45,279 twenty point four, we dropped the point four, it's still one twenty okay, 281 00:21:45,440 --> 00:21:49,119 So just wanted to make it clear For all you purists out there that 282 00:21:49,319 --> 00:21:53,519 say it makes a difference, it's not going to make a difference. Okay, 283 00:21:55,279 --> 00:22:00,839 but you do you personally. I'm doing this because I'm following the way 284 00:22:00,880 --> 00:22:07,279 that you're the the what is this the the ugliest book goes. But I'm 285 00:22:07,319 --> 00:22:11,319 just trying to as I'm throwing these tidbits out there. Uh, it's not 286 00:22:11,359 --> 00:22:12,400 gonna make a difference. If you want to use one point seventy two, 287 00:22:12,400 --> 00:22:15,799 and again I try to kid students into that mode. That's what you're gonna 288 00:22:15,839 --> 00:22:22,200 be using. The other thing that we do is people know that without having 289 00:22:22,279 --> 00:22:26,839 to think about it. They know when they're doing transformers, if it is 290 00:22:26,119 --> 00:22:30,680 for eighty, then you're gonna use eight thirty one. If it's a two 291 00:22:30,680 --> 00:22:34,839 to eight, you're gonna be using three sixty. So that typically people already 292 00:22:36,000 --> 00:22:40,200 know that and then they kind of gravitate towards that. So anyway, you 293 00:22:40,920 --> 00:22:45,400 get the gist of what we're doing here. Okay, so one twenty primary 294 00:22:45,720 --> 00:22:51,240 for this one hundred kVA transformer with one percent impedance. So now let's do 295 00:22:51,279 --> 00:22:55,400 the secondary, same thing, one hundred thousand on the top. Remember that 296 00:22:55,440 --> 00:23:00,319 doesn't change primary to secondary. That you know, watts or watts va volt 297 00:23:00,400 --> 00:23:06,480 dampiers is the vault dampiers. Okay, it doesn't change. So we're going 298 00:23:06,519 --> 00:23:11,880 to do one hundred thousand, and in this case it's three sixty because that 299 00:23:12,039 --> 00:23:18,480 is two eight times one point seven three two is three sixty point twenty five 300 00:23:18,559 --> 00:23:21,480 six. So you could drop the point twenty five six and just use three 301 00:23:21,559 --> 00:23:25,960 sixty. But also for you others that want to know what it is at 302 00:23:26,079 --> 00:23:29,480 just one point seven three, then you can do the times one point seven 303 00:23:29,559 --> 00:23:32,880 three and that is three fifty nine point eight, which you would round to 304 00:23:32,920 --> 00:23:36,359 three sixty. So in that one, it's just three sixty. Okay, 305 00:23:36,519 --> 00:23:41,759 use three sixty, all right, So one hundred thousand divided by three sixty, 306 00:23:42,519 --> 00:23:48,480 which is the two eight square rooted of three uh, and that is 307 00:23:48,759 --> 00:23:52,279 two hundred and seventy seven point seven, which is going to round okay, 308 00:23:52,319 --> 00:23:56,599 point five and greater amps. We're going to round to two seventy eight. 309 00:23:56,599 --> 00:24:02,440 So I have a primary of one twenty and a secondary of two seventy eight. 310 00:24:02,839 --> 00:24:07,559 Now, in order to find the short circuit ampur rating at that secondary, 311 00:24:08,079 --> 00:24:12,759 we use the same formula we did before. The only difference here is 312 00:24:12,799 --> 00:24:17,720 now it's one percent versus in the last one it was two percent, so 313 00:24:17,880 --> 00:24:22,720 one percent would be Take that one, move two decimal spots to the left 314 00:24:22,880 --> 00:24:26,680 at a decimal and you got point zero one. That is one percent. 315 00:24:26,400 --> 00:24:33,079 So it's two seventy eight, which is the secondary current divided by a zero 316 00:24:33,119 --> 00:24:37,559 point zero one, and that gives me twenty seven eight hundred ampiers and that 317 00:24:37,799 --> 00:24:44,359 is the short circuit ampiers at that secondary Now again, if you want to 318 00:24:44,400 --> 00:24:49,240 get further down secondary terminals and you want to get on down, then you 319 00:24:49,240 --> 00:24:53,680 know there is a method that is in the ugliest, but it's also an 320 00:24:53,680 --> 00:24:59,319 app you can get which is called the Cooper Bustman app, and it's a 321 00:24:59,359 --> 00:25:02,200 great app to have on your phone. Shout out the Cooper Busman. They 322 00:25:02,240 --> 00:25:06,680 do a great job, so they're always at your fingertips. When you would 323 00:25:06,680 --> 00:25:08,359 want to do one of these kind of calculations and have it, maybe you're 324 00:25:08,400 --> 00:25:12,119 doing available fault current calculations, or you got to do labeling or whatever. 325 00:25:12,720 --> 00:25:17,279 Usually the utility will give you that information to the service or even the value 326 00:25:17,279 --> 00:25:21,240 at the transformer. Then you can calculate that out from the transformer to your 327 00:25:21,240 --> 00:25:25,440 service. YadA YadA, YadA. But anyway, that's a good start for 328 00:25:25,519 --> 00:25:30,839 you to be able to figure all this out and give you a good start, 329 00:25:30,680 --> 00:25:33,119 and it also allows you to get the numbers that you can use to 330 00:25:33,200 --> 00:25:38,680 plug into your your cooper busman things like that based on whatever transformers that's sitting 331 00:25:38,680 --> 00:25:41,720 there, based on the stuff that's from the name plate, the impedance, 332 00:25:41,799 --> 00:25:47,079 the KBA, the three phase, the voltage, all those type of things. 333 00:25:47,680 --> 00:25:51,359 You can be savvy enough to calculate this stuff out. Okay, so 334 00:25:51,440 --> 00:25:56,519 that's kind of all we really wanted to talk about in this episode, and 335 00:25:56,599 --> 00:26:00,640 so it's kind of basics of transformer sizing. I tend to only see that 336 00:26:00,839 --> 00:26:06,319 on exams. The basic examples that I gave you, don't overthink it. 337 00:26:06,440 --> 00:26:11,680 Now. Using these values, obviously are now going to have to size your 338 00:26:11,799 --> 00:26:15,279 protection for your transformer. So you're going to need to go to four fifty 339 00:26:15,880 --> 00:26:22,039 and you're gonna be learning to size the primary protection of the transformer and possibly 340 00:26:22,079 --> 00:26:26,039 needing secondary protection or you have casions where the primary will provide the protection to 341 00:26:26,119 --> 00:26:32,039 the transformer both primary and secondary protection. And then of course you're sizing your 342 00:26:32,039 --> 00:26:37,000 conductors and all this kind of stuff. That's for a totally different episode. 343 00:26:37,200 --> 00:26:41,359 Hopefully you've watched my videos on Transformer calculations. We have a whole series of 344 00:26:41,359 --> 00:26:48,319 that available over on fast tracks Tube. That's our video platform, and again 345 00:26:48,440 --> 00:26:51,160 yes it's not free. Sorry, you've got to pay for it, but 346 00:26:51,200 --> 00:26:55,279 again that helps us do what we do, and you know what, you 347 00:26:55,319 --> 00:27:00,240 should be wanting to pay for good education, So we try to give you 348 00:27:00,279 --> 00:27:03,519 the best we can, and that's why we put together that video platform and 349 00:27:03,599 --> 00:27:07,640 it's growing every day. New videos are being added all the time, and 350 00:27:07,759 --> 00:27:12,440 over the years, that's going to be our repository for really just great videos, 351 00:27:12,920 --> 00:27:17,039 and eventually all of our podcasts will be moved to there as well, 352 00:27:17,119 --> 00:27:21,039 so it's gonna be a one stop shop and it's gonna be awesome. All 353 00:27:21,119 --> 00:27:23,000 right, folks, Hopefully you got something out of that, and again just 354 00:27:23,079 --> 00:27:27,559 simply talking single phase and three phase transformers. Until next time, stay safe, 355 00:27:27,559 --> 00:27:30,799 God bless, and remember you can listen to all of our podcasts or 356 00:27:30,839 --> 00:27:37,119 even submit your own request over at Paul Abernathy dot com and be sure to 357 00:27:37,119 --> 00:27:40,960 get our mobile app at our website, or you can even go to n 358 00:27:41,039 --> 00:27:45,720 ec chat dot com and get it directly from there as well. Till next 359 00:27:45,759 --> 00:28:15,759 time folks stay safe, God bless both both fast, nothing b