Understanding System Voltages, NEC 2020, (46min:29sec)

[Music] hi i'm mike holt with michael.com and i really appreciate you taking the time to to watch the videos that i'm producing i do want to just take a moment to give a shout out to god he's blessed me and i really want to say a prayer for everybody's watching this and those that are struggling with so many different levels and i and i pray that it just gives you some strength now i'm going to go one more time when the system votes three days in a row but brian before i get there did you want to say something to uh to our oh yeah mike we have uh we've got a ton of schools that have been watching and just a few of them have messaged me and i told him yesterday and the day before i give them a shout out if they gave me a message so we've got shaw tech watching we've got suncoast schools in florida watching we've got uh three or four different classes from porter and chester i've had guys say hey great class we've got people on from power design again i don't think i'm forgetting anybody that emailed me but uh just been getting a lot of messages from people they are really having a good time and just saying how much they appreciate you taking the time to talk about stuff that a lot of us have just wondered about for a long time and it's good to have somebody just kind of step us through it so just really appreciate that mike well you know what i i think it's so cool you know when i'm in a seminar i'm being paid right and i have an agenda and i've been told what to do and i have to do that in a given time when i'm producing live stream videos and i'm producing dvds again as a project this is unique this is something that i'm able just things i've been able wanting to tell people that it's in my head but i just don't have the ability to do that and i do want to thank dan eric sorry i've been saying your name wrong all these years uh dan called me last night because i wasn't happy last night i left the recording i jumped on my bike i rode for an hour out there and i i was just frustrated because i just didn't like the way it went last night and he said mike he says you're doing great so dan thanks for that and i appreciate that dan you're an amazing father and an amazing son and you're amazing guy and you help us so much with our products so thanks for being on our team ready to go now quickly okay transformers just conceptually it's called mutual induction you have a wire going around a coil and when you carry current through that conductor it's going to create an electromagnetic field that magnetic field in a primary is going to cut the secondary conductors this is all covered in our theory book and that magnetic field on the primary cuts of secondary conductors is magnetic field traveling through a conductor the relative motion between the two will cause electrons to flow on the secondary side short version so get the theory book to understand more of what i'm saying okay now there's a turns ratio the number of terms of the primary relative to the number of the terms of the secondary is how we're able to get the different voltages to step it up to step it down an example right here is showing you to say just using relationships here let's say there were 20 terms in the primary and the voltage of the primary is 480. well that means that each individual winding turn is going to be 24 volts in other words that's the effect of that section and then on the secondary let's just say there were five turns so the ratio is going to be what four to one ratio but each winding is still going to be 24 volts on the secondary because they're really pretty close to each other okay so now if you have five turns on the secondary 24 volts and you're going to get 120. again it's not that big of a deal but there is a relation between the primary and the secondary voltage and it's that ratio that gives us the different voltages to step it up or to step it down quick go real fast single phase 120 240 volt three wire system okay you bring a line one a line two i don't see my neutral here okay we're just bringing a single phase to the transformer okay okay that's a primary whatever the voltage is we don't care uh 120 240 on the secondary we take the midpoint of that one winding and then we we bond that that means that we're going to ground that winding right there and then we connect it to a grounding electrode and line one line to a and a neutral three wire a single phase one winding here's an example what it would look like primary it's basically it looks like this you know just one white one face okay well then the seconder is what 120 line this half of the way 120 half of the way well then the whole way is going to be 240 right so 120 240 single phase you take the secondary winding which is a separate drive system and we're going to bond it to the case and then we're going to take both the case and that excel terminal and we're going to ground it to the earth either at the point of the separatory system or the first disconnecting means afterwards but wherever you do the system bonding jumper that is where you have to do the grounding electroconductor or wherever you do the grounding electric conductor that's where you have to do the system binary jumper but it can be either one of those two locations in a transformer here all right looking at the example here what happens is a fault a ground fault which means defined by article 100 which gives us the definition electrons leave the transformer go to line one over current protection of ice to get to the enclosure there's a ground fault ground fault current is going to the source fault current ground fall current is not going to the earth you can just watch the path here current goes to the enclosure goes to the equipment grounding conductor from the equipment grounding conductor because it's on the supply side of this secondary disconnect that's a supply side bonding jumper and then the sub i'm sorry yeah supply side bonding jumper and then we have the system bonding jumper and then of course the whole thing is going to be grounded so now we're grounding the secondary we're providing a system bonding jumper to provide the effective ground fall current paths for that fall current to get back to the source and what does it do to the overcurrent device probably opens it up in about .03 seconds depending upon the type of overcurrent protection device that you have guess what fulcrum is not going to ground guys so forget about always ground rush you guys are driving okay now let's just look at it again well electrons leave the one phase of the winding of the transport goes to the overcurrent device there's a ground fault this is mathematics here now you can do the math you can show the math okay well you're at a 12 what is this a 12 gauge wire out here and a 12 gauge wire out there you go to chapter 9 table 9 in the back of the code book and you get the resistances of the conductors or you actually get the ac the ac the resistance of the conductors and then you have the system bonding jumpers a supply side bonded jumper and you have the system bondage up where electrons with the source there's a ground fault they travel on the affected ground fault current path they get back to the source provides a low impedance path to do what open the protective device now if i said that too fast that means you didn't see the first video and you didn't see the second video you should be able to understand what i'm saying now mike you go too fast well not if you watch if this is your third time i don't know and by the way there was some math calculations you can take a look all this stuff is from my my bonding and grounding book or my theory book or my understanding nec three phase 120 208 four wire y system now look somebody has decided which system they're going to be using single phase three phase 120 trade somebody's making that decision and a lot of that decision is a function of the electric utility what they have available at that location so don't worry about well how do i know all these different voltages well if you're not in designing them it doesn't really matter if you are designing them then you're gonna have to get with the utility you're gonna have your criteria when do you go to 277 480 when you go to 120 208 and that's not the scope of this program all right 277 i'm sorry this is going to be 120 208 4 wire well 120 120 120 we have three faces in a neutral there's four wire no problem okay 120 120 120 is going to be the wine the phase voltage well then the line voltage from here to here which would be from here which is here to here which is here it's 120 120 and 120. but what's the voltage between line one let's say in line two well you know that because it's not 120 120 it's 120 120 vectorially by 120 degrees out of phase with each other and we've talked about that that was 20.8 inches remember that or 208 volts we talked about be very careful that when you're selecting protection devices that if it's a slash rated breaker like a 122 40 volt slash rated breaker that it's suitable for the system now the maximum voltage between any one line this line right here i think this voltmeter is yeah right here okay between let's say this line right here in in in ground is 120. and 120 slash 240 means the maximum line the ground voltage above fault is what it's talking about is 120 well then of course in the y system that's fine now the higher voltage of the slash means the maximum phase to phase voltage under a fault condition well joy is the maximum so guess what 120 240 volt slash rated breaker is perfectly fine to be used on a one twenty two eight three phase four wire system now straight rated breakers a straight rating on a breaker means that it really is a two forty slash two forty okay and two forty slash 240 which means that the maximum line to ground voltage is 240 and the maximum phase to phase voltage is 240 well we're not going to be using a straight rated breaker because they're not that common and they're not necessary and they cost more money for single phase anyhow i'm adding a new graphic a little different than what we've been doing is to try to show you remember we talked about that delta y configuration well in reality it is three separate phases that's why it's called a three-phase system so they're three separate transformers and it's just a matter how they wire look there's only two wires on the primary of this one phase and there's only two wires on the secondary of the one phase well if the primary was 480 coming in and you had a 120 going out and you wanted to get a 120 208 y secondary well it's a delta so then what you do is this this winding is connected to that corner of the winding which connected that corner winding which connect to that corner winding and you watch this video later on you can slow it down and stop it you'll see that this connection is to that winding it goes to this winding it goes back to this winding they're actually in series with each other and then of course we have points that we're making conductors coming in on the primary side so here are the two wires on the primary of that one phase here the two wires on the primary of the second phase here the two wires on the primary of the third face and this is all done internally of your transformer all you're going to do is going to see this terminal well it's not going to be l1 l2 l3 it's going to be probably h1 h2 and h3 and on the secondary you're not going to see the two wires for the secondary winding of the one and then the two wires of the second phase you're not going to see the two wires on the third it's all going to be done internally and guess what they do here if it's a y system then all three of them are connected together at one point and then the other points have different conductors connected you're only going to see x1 x2 x3 and probably xo they're not always universal but that's a pretty common way so that you're bringing in line one line or you're going outline one line two line three you're coming out with a neutral but this right here look this is connected to this one which is connected at that one which is right there i don't have time to spend more time on this we covered that in theory but at least want to give you an idea that a three-phase is three separate physical transformers that are single-phase transformers that are just kind of connected together all right do you have a question yeah one of the guys uh daniel says would you need a straight rated breaker on a high leg system if any of the poles well a second we're not going to talk about highlight when we get the highlight we'll talk about highlight we're only on y configurations okay so now on the secondary winding just to remind you 250 that 381 which deals with the grounding and bonding of transformers on the secondary side it says that your system body jumper and your grounding electroconductor connection could either be at the transformer as a word here or or at the first system disconnecting mean but they both have to be together system bonding and grounding electrode connection either at the system or the first disconnecting means we're staying on the white delta wise configuration well three phase might is the fault current get back to the source guys it's only three individual windings that are just kind of connected a certain way and the electrons will leave on the secondary and the electrons have to get back to the second because that's how an electrical circuit operates it's not that complicated electronically the secondary go to the overcurrent device there's a ground fault for ground fault current is not going to ground it's going to go back to the winding itself that it came from and it goes along the equipment grounding conductor supply side bonding jumper to system bond and jumper all those three is part of the effective ground fall current path as defined in article 100 and make sure you go to 250 at 485 as well clear the breaker maybe in 0.03 of a second hundredths of a second all right but what happens if a person doesn't install the system bonding jumper well guess what you have you have an ungrounded system which was not intentional and since you have a neutral it's 250 to 20 that talks about what systems are required to be grounded if you have a neutral and if it's a 120 208 or 277 480 it requires that system to be grounded so this is a violation of that rule in addition to that you have an ungrounded system and we didn't get into but beeman's book talks about ungrounded systems and the problems there's there's like eight there's nine different scenarios where you'd have a problem with an ungrounded system that's why it's not a favorite system so you're going to create problems with an ungrounded and you can't clear fog because there's there's no fault return path also using this graphics as an example if you didn't have the system bonding jumper well then it's a floating system if you take a voltmeter between line one and the case and line two in the case and line three in the case having a volt meter that has a low impedance setting in there well then you're going to say zero zero zero but if you go lined one to two two to three or one to three you're gonna see that it's going to be one it's going to be 208 and if you go line 1 to the neutral terminal it's 120 line 2 to the neutral 120 line 3 to the neutral 120. see you should be able to with a volt meter and having the knowledge we've had on these three different videos be able to get to a spot and realize okay i got nothing from line one line two and line three to the to the case but i get one twenty one twenty one twenty to the neutron i get two eight two eight two eight well guess what we have we have us we have a system body jumper that's that's missing and it can create other issues but we're not going to get into those but hopefully this is what you're getting it's a review what happens if you install the system binding chamber both at the transformer which is where i've been showing them in general and then somehow a person sees that strap with that screw and saying okay well there must be a reason they got that in the panel and then they just kind of put that in the panel and they make a connection here at the system separately drive system well now you're going to have parallel path for neutral current you see on every single system is to be bonded and grounded at one time which means you take that neutral and you and you bind it to the case and then you take the case in the neutral and you ground it you don't ever do a neutral to case ground again because then your neutral and your equipment grounding conductor are in parallel violates 250.6 ejectional current violates 250. that 142. um so and it could be a hazard again it's not the place to talk about all those details where do you make the connection of the grounding electric conductor well you need to make it at the transformer the first disconnect means code doesn't care but you have to put the system bond jumper at the same location does that grounding electric conductor have to be connected directly to the xo no because if the exo is connected let's see to the grounding bar and 450.10a says you have to have a browning bar in the transformer well if you're going to go xo to the grounding bar why the heck would you run the grounding electric conductor all the way up to the xo when you got a brownie bar there and it's required to be there but you could if you want to it doesn't really matter either way it's fine there's an example of 450.10a you can see this grounding electroconductor is connected right over here to that grounding bar and this right here is the equipment here's the equipment grounding conductor coming to that bar on the primary and there's an equipment grounding conductor on the secondary and then on that probably that's probably well we have a system binding jumper not shown here all right 277 40 volt 3 phase 4 wire hopefully this words are not like freaking you out you know what this is what the first year apprentice should be learning they should be understanding voltage systems at least you should learn this an electrical theory this isn't something your entire career you didn't know what was going on that's why i'm so excited that i've been able to do this to get you this information that what am i going to be able to do this this is too cool all right sorry i'm getting a little excited i've been told slow down a little okay we got a 277 480 volt 3 phase four wire y system right one two three what color code now brown orange yellow code doesn't really care brown purple yellow because you're thinking yellow orange can't be used for the highlights you put purple doesn't really matter you can use orange you can use purple you can use any colors you want to let's talk about the voltages line to neutral voltages are 277 right and line the ground because neutral is bonded to the case well then line the ground line the neutral the same points it's going to be 277 between the two phases or between the two lines rather it's going to be 480 because it's 277 plus 277 vectorially added at 120 degrees out of base with each other and if you put a tape measure there then we talked about that 480 volts line the line when you use 277 480 when you have it the utility has it there and you got a lot of line neutral loads and you want some high voltages and you're willing to put some transformers to drop it down to 120 208 so you can pick up some receptacle loads and maybe some other lower voltage loads but you're thinking hey i got a school here i'm not making a school 120 208 three phase four wire i'm making it you know i'm going to make it 277 480s that's a designer's decision what happens if the ground fault fall current doesn't go to ground you don't drive ground rods you don't go to ground right electrons leave the source travel back to the source delete the winding they go to the overcurrent protection device there's going to be a ground fault it gets to the equipment grounding terminals on the equipment grounding conductor to supply side body jumper to the system bonding jumper all this green stuff is called the effective ground fault current path which is a low impedance from the point of a fault back to the source and it says for the purposes of opening up or clearing the over current device that's article 100 definition of an effective ground fall current path electrons aren't going to ground all right how about a 122 40 volt three phase four wire high leg system delta well you got line one line two line three in a neutral and a high leg is required to be colored arms placed on the b face of a panel board only not disconnects and not metering closes just panel boards 408.3 e 1 yeah e1 talks about the location and 110.15 is about the color so here's your highlight voltage line 1 to the neutral or to the ground point 120 line 3 voltmeter the ground point which is the same thing as to the neutral point you know the half of a winding 120. voltage between line one and line three which is right here well that's one twenty one twenty straight right there additive directly that would be line one let's say i want to go line three and line oops sorry line three and line one is 240. so line one to line three is 240. line one the neutral is 120. line 3 to the neutral is 120 but the high leg is kind of hanging out here from that reference point which is where the neutral point is or where the ground point is it's going to be 240 volts vectorially added with 120 and if we talked about the ruler and make it you know what's it 24 inches this way and 12 inches that way and then you make that ruler you're going to find out it's 20.8 inches or 208 volts is the high leg voltage based upon the 120 240 configuration system here okay now delta delta highlight look at this configuration right here here's a delta here's a delta secondary and then the center point of that one winding which means you have a neutral here anytime it's the center of a single winding it's going to be the neutral and you can see the high leg is all the way out here in line two i say line two because the code requires the orange conductor to be the high leg terminating on the piano board it doesn't have to terminate i mean in the b phase of a panel board it doesn't have to turn and and in the meter can it's going to be on the right side in the panel board is going to be in the center and if you really want to get creative put the high leg on the a phase in the disconnect that way everything is balanced i'm joking but it's fine to put the high leg on the a phase and a disconnect because that's not a code violation it's fine put the high leg on the right side of a meter because that's not a code violation the only place you are required to have the orange high leg located in the beep base is when it's in a panel board or a switchboard or a switch gear all right let's look at the delta configuration guys it's just three windings three phases and somewhere internally they hooked it up delta and on the secondary they hooked it up delta and they gave you a terminal that would have been xo and it would have been x1 x2 x3 so you just would have gone there now what you could have done proper ppe you know what you're qualified you could have taken a vote meter on the transfer and find out i wonder what kind of transfer i got here well go to line one to the case with the system bonding jumper installed you should have what 120. line two is like 208 oh wait a minute now i got a high leg line three is what 120 okay what about line one the line two don't tell me get back here well line one the line two and a high leg is 240 line one the line three is 240 and line two so you can figure out what kind of transfer if you didn't have a label on there is what are you getting in there all right now what about a fault we have a high leg fault using the worst case scenario well then that's going to be 208 volts to ground when i say ground we're talking about where the exo is connected to the case of the enclosure it's not really ground but we call it ground well then electrons leave the transformer go through the overcurrent device there's a ground fault travels along oh my battery is getting slow here it travels along the effective ground fall current path and then you trip the over current protection device now straight rated breakers delta high lake if there's a fault from the delta high leg back over here that means the ground the fault voltage is going to be 208 we would have to use a straight rated breaker anytime you're connected physically on the high leg because the voltage is the ground is 208 is it one second right we don't here it is volts of ground is 208 and the phase to phase voltage is 240. so slot straight rated breakers are fine for high leg now if you don't put on the high leg and you go to line one and line three only well then you can use straight you can use slash rated breakers we're good and here's just an example where if you had a slash rated breaker and you connected it on the high leg well then that would be a violation and then highlight color 110 15 orange you terminate in panel boards on the b phase and in the meter cans it's going to be on the c phase uh this is a panel board that be on the b phase and at the panel board you have to make sure you put some kind of identification that the b base is rated 208 volts all right brian you had a question on the high leg what was it well we've actually got a few questions i'm going to jump back down to the high leg one and it says uh would you need a straight rated breaker on a high leg system if any poles of the breaker will land on the high leg i just said that if you connect it on the high leg the voltage that highlight the ground in the event of a fault is two of eight volts so you have to use a straight rated breaker all right we've got another but if you don't go on the high leg you can use slash rating right okay we got another one if the system has is does not have a system bonding jumper will the disconnect still work and before you answer that one um just go ahead and cover this too what would happen if the ground fault would occur before the secondary disconnect on the secondary i don't know what system we're talking about so let me go back over to something that people can relate to a little easier so let's go over to a three-phase 120 208 volts system all right brian so take one question at a time so it says what would happen if the ground fault occurs before the disconnect on the secondary right here let me go back let me go right here this graphic right here okay if this fault occurred on the line side okay let's say it goes to this enclosure right here ahead of the disconnect well then if all current would leave it would then go to this enclosure it would then travel to the equipment grounding conductor along this effective ground floor current path in that direction there and maybe you clear the primary because it's it's on the supply side so that's why you have a supply side bonding jumper so probably it'll clear the primary side but it's because it's one winding on the secondary side but then that current travels on the primary side of three winding so i'm just going to say that's what it will do i don't know if it's going to clear it or not it probably will okay before you move from that graphic if the disconnect is used for the system bonding jumper does it need to be service entrance rated if you're going to put a system bonding listen all equipment is going to be rated for service equipment so if you're going to have a disconnecting means it's going to come with a strap and if you plan on putting the system bondi guys if you're going to bind that neutral to the enclosure then that enclosure has to be suitable to have the neutral bonded to the enclosure which means it has to come with a strap so this isn't like a complicated thing i don't want to put the system body jumper in the grounding electrode at the transformer because i want to do it right here at the disconnect well then you're going to get a disconnect that has what a system body jumper we call it a main body jumper but that's for services but it's going to be your system on it so yeah you'd have to use one that you can do it which they make them that's just the way they make them you're going to get them that way all right we've got one more here it says if you have a metal conduit between the transformer and panel does the ground conductor have to bond to the conduit i don't know what a ground conductor is so when you guys start using words that are slang terms i don't understand brian see if you can read it again to me okay if you have a metal conduit between the transformer one second hold on hold on hold on right there let's assume i physically don't install a system bondage a supply side bonus up here okay brian yep you're with me i'm going to put a metal conduit between those two with metal couplings metal lock nuts okay that is my supply side bond and jumper so they just said you're running a metal conduit between the transformer the disconnect okay go ahead does the ground conductor have to bond to the conduit i think where this is going is the the issue and you addressed us the other night without bonding bushings guys let me explain this the system bonding jumper is where you terminate the grounding electrode conductor the system not your supply side bonding jumper if you put a piece of metal counter between these two here that doesn't change your system bonding jumper and and also using terms that don't make any sense at all so i i can't do any more than that question because it's it's a little convoluted question and the person doesn't understand system binding jump or not do with the metal raceway that's unrelated well the only other thing i want to do is i see that tom dimitrovic joined us and i want to say hi to dom tom hope everything is going good for you buddy i love tommy eaton got me it's a good breaker's coming right all right we are now going over we got done with the high leg and now we're going over a lot of stuff here corner grounded delta system not that common but research reminded me mike because of the problems of an ungrounded system because there's beam and talks about eight or nine different reasons why you have failures ungrounded systems and the equipments associated with that that you really want to go with the grounded system then they took these ungrounded systems they just corner grounded them and so now we're going to talk about well how do you do if you do a corner grounded delta system three wire okay well you have line one line two line three the the grounded conductor which is right here this is that corner grounded right here actually it's bonded and then we ground the equipment but whatever that's your grounded conductor i think the practice is line two but it could be line one or line three it doesn't really matter so i'm going to say it's lined to in my example so therefore this is going to be a white wire or a gray wire whatever you want to be there or black wire with face tape or whatever as black white red again there's no color coding required by the code but that might be a common system all right got the corner grounded system and what's the voltage if your corner ground well if you're corner grounded well then that's your reference point period that means that that's zero because then you take it to the earth so your system binding jumper and then you have your grounding electroconductor and then the voltage between zero let's see this is line one to zero is 240. line two to zero when line two is zero it's zero because it's the same point line three which is this winding right here that would have been line one would have been 240 and then line 3 would have been 240. okay we got the concept somebody said well mike you know if you're grounded that corner grounded delta system aren't you going to have objectionable current flow guys you can only have current traveling on metal parts when it's connected to the ground conductor at two points look what we did here on this corner grounded delta system how many times did we ground that secondary system and bond it once whether you're corner grounded whether you center ground it it doesn't really matter you can't do more than one so no there's no people like man i just don't understand you're taking the b phase and you're connecting it to the case i know it's wrong i know it's not going to work i know it's dangerous it's not dangerous that point is connected to that case it's connected to the earth and it's all zero everything out referenced at that is not zero however okay fall current leaves the 240 volt systems travels along the ground fault the effective ground flow current path system bonded jumper goes up inside here bada bing bada boom 240 volt fault opens the protection of ice that was it i had on the corner ground a delta system three phase four wire corner grounded delta system i'm showing a wide delta configuration where you reverse fed a transformer that was delta y where you were supplying 480 down to 120 208 and you decide you know what if i get 40 down to 120 208 i need 480 and i have a 120 208 can i just back feed that little puppy right there and be like now supposedly it's not the best practice to backfeed a transformer however you got to make sure the transfer is marked suitable for reverse fed and you look at the instructions they show you how to do it so now we do not bring a neutral on the primary side of a y system because we don't need a neutral well mike would it hurt if i brought a neutral there well why don't you bring a neutral to three phase motors and not use it so why would you bring a neutral to the primary side of a transformer and not use it so no no neutral in the primary secondary is corner grounded okay they're all 480 in this case here which is correct for 84 84 80. line one [Music] to ground is this winding here i probably should mark them like a b c in the future maybe that way i can see it and that would be let's say that b phase right there transformer that's going to be 480 and then of course this is grounded at one time one time which means this is called a grounded conductor not a neutral conductor because it's on the corner not in the middle that's zero the other phase is 480 and voltage between phase of 484 84 84 80. how do you clear a fault on a corner grounded delta system well if the phase that's grounded is false again guess what you have objectionable current right if you have the neutral i'm sorry it's not a neutral if you ground this to the case here and somewhere over here you have this your grounded conductor inadvertently ground faulted okay well no you're not gonna have me yeah well you're gonna have current yeah what you're gonna have is you're gonna have currents traveling on line two back in how the way the three faces work and then you can have currents traveling on that so a corner grounded delta system if the phase itself grounds again then you are going to have a grounded conductor connection to the case of two locations violating 250.6 ejectional current but if another phase goes ground faulted well then the fault current leaves the source goes to the overcurrent device gets the enclosure ground falls it travels on the affected ground fault current path then it gets back over the system and it opens the protection of ice the electrons are never going to ground guys they'll be driving ground rods trying to make it safe because that doesn't make a difference another day we'll talk about that three phase 40 volt high impedance the best of all systems except you don't get any line to neutral loads on the secondary so you can't have so here you go right here 277 277 277 per phase and then this the system bonding jumper has a resistor or impedance of about one ohm and it looks like this here you can see how it's like a coil so it heats up in the event of a fall and then there's alarms that go off and they tell you hey you got a ground fault out there so here's the alarm on your one of the 277 i don't know if i said one oh it's 277 ohm resistor for the system bonding jumper the voltage from line one to basically here is 277 277 277 and this to here is the same point there is 277 voltage between the lines are 480. how do you clear a fault anytime there's a ground fault the key here is what guys if you don't have a system bonding jumper you're not clearing a fault and if you had a fault at 277 if this resistor is 277 ohms then what's the what's the current of that fault where i is equal to e over r e is 277 r is 277. 1 amp now that is the system you want to install to reduce any kind of arc incident energy at least when it comes to a single phase ground fault application the problem with the three-phase um three-wire high resistive or high impedance ground system is that you have restrictions it can only be installed where conditions of maintenance supervision ensure that qualified persons will service it number one two that there are ground detectors installed and three uh only line of neutral loads are served so you can only have 40 volt phase to phase a single phase or three phase three phase ungrounded three wire delta secondary i thought i already covered that wouldn't oh no that's ungrounded yes right just a quick comment from eric he says uh while it uh fault probably wouldn't melt the fuse depending on the voltage they use relays uh for many other reasons so that the ground fault can um looks like the actuate devices and set settings so it looks like okay so resisted grounding they're using it also to actuate different types of relays and probably initiate disconnection and safety sequences yeah this is not something you go on you buy a resistor 277 ohms and you're sick of an error you're getting a high impedance grounded system and then of course you follow the instructions this is just showing you a piece that's within the cabinet itself okay so there's your resistance within the enclosure the enclosure has meters and relays and controls and what have you it's a cool system i love it three phase four three wire 40 volt ungrounded system well here's your ungrounded system the problem with ungrounded systems is i won't say they're unstable but beeman's talks about um there's eight or nine different scenarios where when you have a floating system like this there's re-striking ground faults there's feral residence conditions on on situations and there's there's lightning and static this this insulated winding and all the insulated conductors are kind of like floating in the air and they start end up getting a charge and they keep getting a charge and high and high enough till it gets about six or eight times the rating of the actual line the ground voltage and or rather align the line voltage whatever it is and then all of a sudden it discharges we'll want to discharge it discharges in motor windings and in relays and things that don't have the same insulation properties of conductors so it damages equipment so ungrounded systems i won't say they're unstable but they're not desirable unless there are applications and places like i think in ships and other locations but i don't know enough about that somebody decided that's what they want okay so what does it look like well if you have an ungrounded system you're going to have to have a ground detector so they can know that something happened we talked just about the lights that back in the 40s and 50s they use lights today they use ground detection systems you know you can see something like that okay well years ago it had lights the way they were configured and the lights were i think they were 575 volt lights uh basically uh 277 would be two i don't know what the bolt is here but the ground here i don't know what the volts is the ground but what it was less than then five seven five seventy five seventy five so the lights were dim and then in the event of a fault then i guess brian one light went off no did it get get brighter yeah the light that faulted went out and the other ones got brighter okay the default one and the other ones got brighter meaning okay so we don't really care that's old stuff so some of you guys know i'm talking about how do you clear a ground fault well if you have an ungrounded system when there's the very first fault then there is no vault and there is no fault current because it can't get back to the system ground detector goes off if you don't clear default before a second fault occurs now you have a phase to phase fault that's why the code says for ungrounded systems that you have to make sure that all the metal parts are actually bonded together just as if it were a grounded system for the purposes of that that all those metal parts would be serving as an effective ground fault current path other voltage systems there's zigzag systems that actually uh you derive a neutral the other ones we're not driving neutrals because they're just logs we connect to them there's open delta systems that we're not these are unique special systems that we're not going to talk about i don't think we have many of those new today and i'm not going to get into that and then you have the old two phase five wire systems and uh not gonna get into that man we've done this three times i'm done really i'm done i can't there's nothing else left there i haven't been able to sleep trying to figure out how to make it simple and i thought i could do this in 20 minutes you didn't didn't do it we got time for a couple questions mike yes we have time and then i'm going to try to jump into something different just to finish up okay um i got a question from adrian and he says other than the fact that they're both breakers what is the thing that makes a slash rated and straight rated breaker different from each other okay tom demitrix is on here and he can tell you what it is but in simple understanding there's a term called short circuit current rating what that means is that everything has a given short circuit current rating and in short circuit currents can create heat and it's going to create magnetic fields let's just do something simple of a of a breaker if a breaker is rated for 10 000 amperes well it's rated for 10 000 amperes at a certain voltage so that current is a function of a certain voltage and so let's say at 120 it's rated for 10 000 amperes from line to ground well if you have a higher fall current line to ground than 10 000 amperes well then it's going to get hotter than it was designed for and the magnetic forces are going to cause this thing between the other two faces to move around so this is a an engineering decision so when they engineered that breaker they said okay let's test line of ground faults and it was rated for 10 000 amperes for 120 and they tested it at 120. then they tested phase to phase on the breaker at 10 000 amperes okay at that voltage that breaker so everything has an ampere rating at a given voltage and so that's a configuration so if you want to know more about how do they actually i don't know how to test it you know what's important you better understand all the different voltage systems that you could possibly run into you better know what the volt is line to ground because you can just take a voltmeter you can check that and that's going to be the the lower of the two voltages and you better make sure that that slash rating that lower voltage is equivalent to that one thing and guess what you're not putting a 120 240 volt slash on a high leg conductor but you can put it on line one and line three because that maximum line to ground voltage is 120 but line the line they were 240. so guys sometimes you got to be careful that you don't you don't throw more in there and then you lose with the essence what's important so just be careful yes okay it looks like the last question you may want to send them back to yesterday's and tuesday's videos they're looking for you to elaborate on auto transformers again uh we covered auto transfer yesterday and there isn't anything to elaborate you buy something it's single face and apparently don't really make three phase auto transformers and and so when i'm not going to get into that so an auto transformer is and we covered this yesterday the very last 10 minutes of yesterday is that you bring in let's say 208 and you want to come out 240. so you go out to the store and you say hey i want an auto transfer where do you want it from and you mark that goes input output all the different things configuration whatever it is and you pick the one you want yup so yesterday it's just one winding and you know what i don't know what my theory book is oh i gave my theory book away to a guy working in my house today so it's in my theory book

Channel: MikeHoltNEC

Views: 48,951

Keywords: Mike Holt Enterprises, Trainer, Electrician, NEC, National Electrical Code

Id: 9ZZZR8Me4nE

Length: 46min 28sec (2788 seconds)

Published: Tue Mar 30 2021