5 of 7 System and Equipment Grounding (13min:48sec)

well then what's the purpose of grounding that is what we really need to talk about here is a little snippet that I took out of industrial power systems handbook by by a gentleman named Beeman who wrote this in 1952 this is one of the chapter I think is chapter 5 it says this the word grounding is commonly used in electrical power systems to cover both system grounding and equipment grounding ok so now make a note here whatever it said number 5 you guys make a notes you anybody keeping track of these things number 4 is it number 5 so number 5 is that we have system grounding and equipment grounding ok so now we got it figure well what the heck is system writing what's equipment grounding all right now there are two types of systems you have an ungrounded system let's take a look at this take a look at the secondary winding again you are assumed taking this course that you understand electrical theory this is a system if you take a look at this system the system secondary is insulated and these conductors themselves are all insulated and there is no fault none of these conductors are connected to any equipment that means that this system is ungrounded the system winding the actual Trant winding it's not connected to anything that could be an extension to the earth and always it's not connected skywrite to the enclosure that has a connection to a conductor that has a connection to the earth so therefore that system is not grounded ok well then there's no grounding of an ungrounded system but we're talking about mic we said okay we're talking my assistant grounding an on ground and while in system grounding you could have an ungrounded system that's system grounding right it's an ungrounded system now let's go to the next one yeah but what are the problems with ungrounded systems see there's a problem with an ungrounded system is that equipment can easily be damaged from transient over voltages caused by indirect lightning Andry striking ground faults now if you heard what I just said you should have no clue what I'm talking about but take a look at the next slide over voltage is explained clearly in this book and that's your power system handbook by Biermann and I just ordered this online it's a 1952 book and the books that were written in the 40s and 50s engineering books and I was that man some of that stuff was just golden and in this particular book here's what he says he says over voltage sources there are many varied sources of over voltage of sufficient magnitude to be damaging to the installation of AC industrial power distribution systems in this chapter the mechanisms of which they prominent over voltages are created will be described and prevented measurements measures suggested treatment of the Fallen will be included static static electricity you need the ground that physical contact with higher voltage line what do you do resident effect with series inductor capacitor circuits call fair resident repeating intermittent short circuits that's a restrike in ground fault switching surges for zero current interrupting I am no clue what most of that is even talking about because it because it's the problems associated with ungrounded systems so let's go back to the graphic here so if you go to an ungrounded systems you have problems and so what Bering Beeman is saying is they listen you know we started the industry with ungrounded systems and we got just a lot of problems with over voltage so he suggests what you need to do is you need to go to a grounded system all right let's talk about a grounded system now a grounded system take a look at this winding here's a Y secondary it's insulated conductors and all the conductors leaving the windings are all insulated ok except look right here we take the actual winding itself we run a wire down the grounding electrode conductor over to a structural steel which is ultimately connected to the earth so now we've taken this system and we grounded it now why do you ground a system you ground a system because Bement explained these eight things including lightning and all these different things that can take place whatever they happen and you can have an over-voltage on the insulated system that's not grounded and this capacitor charge is induced energy all that stuff that's on those conductors there could be a problem that there's going to be failure rate of equipment so you ground the system so you say well why would you not want an ungrounded system there's there's reasons that you have ungrounded systems and there's reasons why you don't on ground assistance I'm not going to get into systems but pretty much for today's installations we have grounded systems because they found the problem with ungrounded systems we want to ground the system all right let's move on here so a system is grounded take a look right here a lighting event outside strikes it induces energy it brings in energy into the building it expands and it collapses that energy that will put it will push those electrons in that building on those insulated conductors that energy is trying to get to the earth and if you don't provide a path to the earth you're going to be damaging equipment that's what Beeman was explaining back in that book that we talked about there so take a look here if we ground the system then that induced energy and all those conductors is going to come back to the system and it will use that grounding electric conducting get to the earth to be able to dissipate that that that magnetic pulse of energy we're not talking about clearing a fault that's why the code says why is the what is the largest conductor required to a to a ground rod the answer in 250 66a is what six gauge so if you have a 2,000 amp service and you're using two ground rods as your electrode what size you need six gauge why because we're just trying to bleed off this magnetic pulse of energy to the earth so that we can have this system so that it doesn't have an over-voltage condition so that doesn't get damaged but what's the sizing rather the routing of the grounding electric conductor look at this graphic right here that grounding electric conductor it's a note informational note and it tells us this that that conductor should not be any longer than necessary and we should not have any unnecessary bends if you're anything about surge protection you want the wires to be what as short as possible see lightning is a high frequency DC pulse of energy so it's high frequency DC pulse advantage on one-way roof as well what we want to do is have that wire short as possible because see inductive reactance is 2 pi FL F is the frequency you go from 60 Hertz to let's say 10,000 Hertz or 20,000 Hertz well now that wire had a certain amount of resistance the inductive reactance on that wire added to the resistance the impedes that I wire is astronomical see what you don't want it's a long grounding electrical conductor going to some great ground you might have a great ground let's say 100 feet away a well casing a well casings 100 feet away man you're not going to get a better connection to the earth in a well casing there's a hundred feet the ground I mean come on that's the whole purpose of it there's this there's a term on the earth to go to the problems you get around a hundred feet of wire you run 100 feet of wire you're carrying high-frequency DC pulse to that well case and get to the earth you'd be better off running a six gauge wire right there ten feet long to ground rods and then if you're talking about the purposes of grounding so we got to understand what is the purpose of grounding now that has to do with system grounding and Beaman said there's two types of grounding there's system grounding and there's equipment grounding let's move now over into equipment grounding now it's really metal equipment grounding is what we're talking about it's real simple metal parts of electro equipment are grounded to reduce arcing within the building structure from induced voltage from indirect lightning now equipment grounding is different than system grounding with electrically it's the same you're the wire looks the same here's what I'm talking about you get a system which is insulated windings with insulated conductors inside of a building and it's on ground that you have a lot of different nine or eight different conditions of over voltage it causes this high energy on these conductors they end up destroying equipment they found that out I mean that's a major problem so we then go to what we then go to system grounding what a system grounding you take these insulated systems and these insulated conductors you make one connection from the exo terminal you go to the earth we can bleed off that energy we're talking about conductors you're not likely to kill anybody if you don't have proper system grounding because it's the equipment themselves is going to fail but equipment grounding is different follow this concept take a building with all kinds of metal all over the building steel piping electrical boxes there's no conductors in there at all and none of this piping in any way none of these metallic parts and none of the metallic parts is connected to the earth it's not grounded a lightning event outside it does what it pushes those electrons on all those metal parts where is that energy trying to get to it is a DC pulse high-frequency high-voltage huge amount of energy that's trying to get to where to the earth if you don't make a connection to that there might be some plumbing pipes in there or some other thing beside the electrical that has some connection to the Europe inside the building what happens in there's arcing side flashes called so there's million volts of induced energy on this electrical system metal parts has no place to go to and it's a I'll just go over to that steel column or I'll go over to that plumbing pipe while that's doing side flashing it could go through something and combustible it could cause a fire in addition if you're in a building that has metal electrical systems and the equipment is not grounded you have a lightning event outside inducing huge amount of voltage you having to be standing next to something while the lightning strikes at that instant you could have a side flash to you because you're the capacitor path over to the earth so equipment grounding is absolutely critical that the metal parts of equipment they're all what everything in the building is all connected together another word would be what bonded together and then we take all the metal parts and we deal with it we make sure we go to the earth at one spot in only one spot only take a look at this graphic and how do we do that well at the service you run a grounding electric conductor right from that equipment which is connected to the neutral and you go to the earth or you got a remote building you're running a feeder to a building you do what you run a grounding electric conductor from the equipment to the earth this is called equipment grounding that we want to make sure that the equipment is connected to the earth now are we carrying fault current I'm we grounding because we're going to try to clear a fault no you can't clear fault we're grounding it's the earth it's just a spot that you it's it's a spot that you put DC high-frequency pulse of energy just to the earth one way we want that wire to be what as short as possible we don't want a whole bunch of bends and we wanted to be right there and so that is called equipment grounding well Mike if I run PVC from the service to a remote building and I bring an equipment grounding conductor PVC do I still have to have a ground rod in the building of course understand something what do we want to do with the grounding electric conductor as short as possible to an electrode not some wire inside of a Raceway that goes 100 feet from one building to the other building no no no that's an equipment grounding conductor why do you have an equipment grounding conductor that was to make it safe it's your protective conductor the Europeans label it as a PE protective earth conductor it's your protective conductor so your green ground wire is your equipment grounding conductor because that was I think number which one was the one about the clear fault was it number three have an equipment rounding conductor on our notes falling before number four remove a D energizer sir so equipment grounding is to provide a path from the energy that's induced on the metal parts to the earth and let me explain something that's really important understand grounding is electrical systems recording NEC is not for lightning protection if lightning directly strikes an electrical system whatever it does to it is what it does to it and then you go and you fix it the NEC is not a lightning protection standard if you want to protect the electric equipment from a direct lightning strike then you would put NFPA 780 lightning protection systems and that way it's designed to capture the energy of a direct lightning strike to air terminals parallel those conductive paths to the earth and take the energy we're talking about so seed lightning goes where's lightning where's it come from how does it work out well here we go energy from the earth is going to be raised and brought into the atmosphere okay these Sun so you have this energy now you have the energy raising atmosphere it goes up it gets cold when it gets cold gets what happens in the the molecules become ice the ice particles start bouncing across each other and they start breaking apart you get negative charge positive charges now you get charged all over the place now you're having equalization of electrical charge it's just the way things work out well yep lightning goes from cloud to cloud cloud earth earth the cloud even from earth to space it's called sprites okay so there's a and you know what talk to anybody who knows lightning to tell you we really don't know how it works so let's understand some nobody knows how it works but we do have some concepts that if lightning is trying to equalize itself and there's a discharge if it directly hit something it's going to do whatever it's going to do to it but it we're trying to protect against electrical systems or voltage and equipment over voltage when lightning doesn't strike the equipment lightning strikes the earth it induces energy that energy that's being induced is seeking the path to the earth and if it doesn't it will get side flashes and cause any causing fires

Channel: MikeHoltNEC

Views: 195,910

Rating: 4.8616252 out of 5

Keywords:

Id: xn4az8EuNO0

Length: 13min 48sec (828 seconds)

Published: Tue Nov 26 2013