Grounding Versus Bonding (26min:26sec)

first thing is going to be electric shock death and/or severe injury occurs whenever both these pushes electrons through the human body particularly through the heart we've talked about this earlier currently the power supply and they're always returning what to the power supply they might be alternate paths so we have current leaving the source going through the light bulb current leaving the source going through the human body anytime you have current going through the human body through the heart in particular that's where the danger is of electric shock and electrocution hand to foot it might be hand to hand that's connected to something conductive where the electrons are returning back to the source the electrons are not going to ground the electrons do not take only the path of least resistance they take all the available paths and the electrons are going to go back to the source traveling through whatever it's traveling through in parallel with the loads so let's go back to our graphic here electrons leave the source travel the light that human being because there is a conductive path back to the earth that's a danger hand to foot hand a hand making contact with something that's conductive and maybe Mike who's with me here on the left hand side of my hand here maybe Mike will be able to make a graphic where on the left side of the graphic we show hand to foot we can do something more pictorial so you can see beside the one-line diagram and also on the other one where it's hand to hand we can see something more conductive so what we'll try to put that together to make it a little better let's go on to the next slide electric shock hazard up death and severe electric shock can occur whenever voltage exceeds 30 volts and dry locations or 15 volts in wet locations nobody knows where this 15 a 30 volt dry location wet location is and whether it's even true or not but it seems to be what's out there in the industry that if it's over 30 volts that it's considered dangerous and if it's under 30 volts on a dry location it's considered kind of okay that's where you get your class two wiring and power supplies on chapter nine I think it's table 11 and maybe 11a and 11 B and again 725 what a class-2 circuit is and so there's that 30 volt then when you get into wet contact resistance it kind of drops down to 15 volts but listen if you are immersed in water you're in a swimming pool you're in a marina you're in water forget about 15 volts being dangerous we're talking about small amount of voltages can put you in a state of panic or it can put you where your muscles are in parallel with the water which is in parallel with the current flow the voltage grading can be quite large so swimming pools marinas anything where your body is immersed in water is really really a bad situation all right let's talk about further the severity of the shock is dependent on the path through the body follows and the magnet or the current so these numbers I want to change I think in the future and just simply change these or these are representing percentages of a thousand so I'd rather just make this like instead of being a hundred percent of a thousand being 100 make it a thousand and if you go from your hand to your hand its what a hundred percent of a thousand or it's a thousand ohms if you go from a hand down to your foot it's a hundred percent of a thousand which is a thousand ohms so we'll redo this graphic here and just make them by adding zeros to everything well what about your hand to your chest hand to your chest is forty percent so in other words if you're leading on let's say a bar choice and it's conducted back to the source and you touch an energized conductor was hand to the chest well now it's not a hundred percent of resistance it's forty percent now these are just numbers that every condition changes because you contact resistance or a lot but let's just say the standard is a thousand ohms based on the standard standard based upon this kind of contact resistance from your hand to hand is a thousand ohms hand to your foot it's a thousand ohms hand to your chest is 40 percent or what four hundred ohms see it's the current through your body that makes the difference but the current through your body is a function of the formula AI is equal to e over R let's go to the next slide here so the magnitude the amount of electrons is dependent upon the voltage and the resistance now let's talk about both these resistance for all practical purposes we're saying the voltages are constant it's a 120 it's a 277 we whenever you see like 122 8 120 240 277 480 347 600 it's the lower voltage is the line the equipment grounding conductor or line the nutribullet is that we're talking one now of course you could touch face to face so if you go face to face it's going to be 240 208 480 what have you so to make it simple I'm going to work off a 120 volt examples so if the voltage is 120 then your contact resistance a thousand ohms we could calculate the current well if you go from hand to hand it's what 120 out of thousand ohms hand to your foot 120 or thousand ohms hand to your chest while you're leaning on something well now that's what 40% or 400 ohms so you can see as you reduce the resistance what happens to the current the current is going to go up the greater the current the greater the likelihood that you're going to have a problem when it comes to electric shock or electrocution let's look at an example right here it's a 120 volt circuit electrons leave the source they travel back to the source via the neutral conductor however there's a fault to the enclosure and the enclosure is not connected to an equipment grounding conductor the person makes contact between the hand and it make contact with the other hand to something that's conductive and then those electrons return back to the source in that particular example we have a 120 volt circuit and we have a 1000 ohm resistor which is the human and based upon that formula I is equal to e over R which is 120 over a thousand we have a hundred and twenty milli amperes another way to look at it plugged into an outlet its energized goes to the heart to the head that's hand-to-hand as a thousand ohms and that returns back over to the power source now I'm going fast it's important that if you you're catching pieces of this but not the whole thing go to the whole DVD as far as the section concern may be go back to a couple times as some instructors or maybe are somebody else all right you know or get the DVD that I get into details in the grounding and bonding all right let's go a little further there but before I do that take a look at this particular graphic hand to hand is a thousand ohms 120 volts is 120 mm amperes that should mean nothing to you other than 120 wonder what that means well here's what it means if you're between 0.3 or 0.4 of a milliampere we're talking about three tenths of one one thousandth of an ampere people are gonna say you know what I feel a tingle that I feel it tingles I feel I just feel something if you start getting close to 1 milliampere now they say hey I feel something and they let go and I go hey well something's not right there it's different than like you feeling a tingle below a half a million ampere 1 milliampere then letting go that level is around 1 milliampere now let's go to the next point here maximum let go that's where you cannot let go this is the most you can go and aptly passed this stretch whole point take a look at the graphic here you are not permitted to let go females the studies have shown is a 10 milliampere above that she could not let go and males above that he cannot let go now it's not because women a more sense of the man I got 5 daughters and a wife and we're not going to get it that at hoping ok it has to do with mass the studies that was done back in 60 I think it's USC University Southern California and Dazzler denzler whatever his name is huh al Berkeley Cal Berkeley and so he had his students me take the girls here grab this hold this and let it go whenever you can well at some point you know you see on the internet you can see the pictures and you see them all contorted at they figured ok couldn't let go that number ok yeah we can here come up on average they did the women in the class and the men in class maybe today they don't like those kind of studies in your college class ok but we got the information that's how we got the information on GFCIs would it become a safe standard the reason the females are 10 in the male's are 16 is because the average weight of the female at that time was a hundred pounds the average weight of the male in that class at that time was 160 it's linear so if you're 200 pounds your let go threshold will be approximately 20 mili-amp you if your little child let's say 50 pounds your Mac Michael threshold is going to be about 5 milli amperes so let's go back to the graphic depending upon your mass is your Lego threshold once you start getting into a 50 milli amperes 50000 amp 275 now depending on time now you're going to get into what is called ventricular fibrillation ventricular fibrillation is where your heart Quivers it because see the heart has an electrical signal it the heart it's you see movies where they pull the heart out I got holes of the heart's pounding like that that's true the heart itself has its own power supply it has its own signals it takes care of itself this is not something that's done by the brain it's done by the heart itself well if the heart has a power supply and it's sending out the signal to the muscles to get it to do what it's do you get something to go pass it in some way that you get the control circuit in there to get confused it's trying to reset itself it's it's trying to get the thing right and so it keeps trying to reset itself and it can't get there at all the electrical signal the body is 40 Hertz electric power we work with what 60 Hertz in the United States Europe is what 50 Hertz very very close to the same frequency between the hearts and the brain the way the electrical systems work in the United States now everything we do with our body is all electric I mean every my hand moving my muscles my brain my thinking my eyes by eating it's everything it's an electrical signal so when you bring us a signal coming in at a certain frequency at the wrong time to the heart as it goes past the heart now you have ventricular fibrillation so what is we're trying to do you're trying to use a defibrillator you're trying to say stop stop and then I'm assuming the defibrillator attempts to stop that signal and it probably hits it again and I don't know how they design those things that try to get the signal going again that's where CPR comes in when a person's going through ventricular fibrillation blood is not moving in the brain in the body so then you do CPR you breathe in 21% oxygen you exhale into that person 16% oxygen you try to do compressions at a certain number of compressions with in a myriad minute during a certain rate per compression status okay that's that's going to be CPR makes you have CPR all you're attempting to do during CPR is not in any way to get the person that's the heart defibrillating you're just trying to move blood ever so slightly to the brain just move it ever so slightly because what has the oxygen brain needs oxygen no oxygen the brain dies so our problem in electrical systems is that if somebody gets a current traveling from one part of the body through another part of the body it travels through the heart at a certain frequency at a certain magnitude at a certain timing your heart can go to ventricular fibrillation and then you die so we have to be very careful 90.1 said what the purpose of the NEC is the practical safeguarding of persons and properties arising from the use of electricity so we need to understand well what could cause an electric shock let's go a little further now now we can use this in a different table to look at that electrical sensation pretty small less than a half a million pure I feel it I'm not comfortable 1 milliampere harmless for most people anyhow 99.9% of population probably 4 to 5 milli amperes with the range you should be fine you start getting above 5 milli amperes it's very very painful you start getting around 10 to 15 to 16 depending upon your mass you might get the point you can't let go if you cannot let go so you're not going to get killed at 20 milli amperes but if you can't let go well something's going to happen here because you're going to start sweating what happens to your contact resistance it starts going down and as soon as you can go through the skin and you burn through the skin guess what we're now in two veins right we're now in the blood which is an electrolyte which is a conductor somewhat conductive anyhow you have nerves they're designed to be carrying currents and you can imagine how the body reacts to that you have the parallel paths of all the muscle fibers so all this is contributing and it takes micro amperes to the heart to get the heart to go into defibrillation we're not talking milli amperes we're talking about millions about 50 millions of amperes through the heart the wrong time the wrong frequency if you can get it right to there boom we're going to die so that's the danger that we have here so how do we solve this problem with electric shock well the way you solve the problem electric shock is a couple things how do we handle electrical systems well we insulate the conductors right we don't want to be going somewhere in lose if you see a cover that's off a plate of a receptacle is there a chance that somebody could put the fingers in there and contact the energized part we all know it's obvious a switch a receptacle I'm sure you've walked around malls and shopping centers and streets and into public places all over the place and you see conductors that are insulated that are being exposed now because there's such this happens so often sometimes I think we become desensitized not recognizing one touch for one instant can kill you could put you in the ventricular fibrillation and then you're going to die in a matter of a few minutes so we insulate the conductor's now do we insulate the conductors we put them in enclosures and we require the enclosed to have what to have covers and they be protected and we make sure that we could isolate contact to those parts however even if we do all that properly there will be times that a wire through vibration a connector coming off the wire actually makes contact to a metal enclosure once you make contact with a metal enclosure that's when we have to deal with it we have one of two ways to deal with it number one don't do anything about it leave it energized that means that if one enclosure is energized that means the entire building could possibly be energized or two if a conductor that's energized makes contact with a metal enclosure that could energize it and then expose to the people because the enclosures are supposed to protect people from making contact when the conductors but they themselves can become energized because of a fault then we have to turn off the fault that's the only option let's look how we do that now this kind of a really really busy graphic but we're going to work the best we can with it you have a transformer and the current leaves the power supply goes to the disconnecting means of the secondary side and let's say an ant meter is recording this and there's 600 amps that leave it it travels to the enclosure and from the enclosure goes on the equipment grounding conductor through the supply side bonding jumper over to the equipment grounding terminal that's now going to be required in the 2014 code up these just the bonding jumper back to the source it would have you put 600 amps on a breaker let's say this 100 I breaker well we are going to be tripping the breaker so the concept of providing protection of people is to make sure that everything that's metallic is connected to an equipment grounding conductor and we have to make sure that all the equipment grounding conductors are connected ultimately back to the equipment grounding conductor at the source which is going to be your grounding terminal and we have to make sure that we bond that equipment grounding terminal at the transformer to the system inside to the system itself via the system bondage number if you provide proper equipment grounding conductors proper terminations proper connections all the way back to source that equipment grounding conductor that supply side bonding jumper that system bonding jumper and all those interposing connections back there is called the effective ground fault current path and that's how we get the electrons from that fault back to the source to open up that protection of ice it's that simple I don't have to go any further in grounding and bonding they just simply say make all the metal parts connected to the equipment grounding conductor connect it back over to the equipment grounding conductor at the source connect the source over to the neutral bada-bing bada-boom we're done now how fast does it take the trip the breaker well if you have a 20 amp breaker and you have 40 amps where the fault this is called your time current curves and look at the red one this is the minimum unlatching time it's expected so 40 amps manufactures do this the quickest you can have on a 20 amp breaker under a 40 amp fault the quickest it's going to open is approximately 1/2 of a minute now the maximum time that it would be expected to open is you go all the way up to the Blue Max one latch in time up and over that's a hundred and fifty minutes that's going to be 200 that's going to be two and a half minutes sorry 150 seconds that will be two and a half minutes so a 20 amp breaker if there was a 48 fault what taking anywhere choosing anywhere between a half of a minute to two and a half minutes open that's just the way it works but what happens if we can increase the fault so we can raise it from 40 EPS let's say 200 amps look at the time current curve the minimum unlatching time would be approximately 5 seconds the maximum is going to be 20 seconds so now if we have an effective ground fault current path the lower the impedance because has to altered a current if we use an awl thinker the lower the impedance of that that in that fault path the higher the current the higher the current what the quicker the device is going to open devices are not going to open instantaneous it's called inverse time the higher the current the quicker the time so our goal was always to do what make sure that the fault could be as high as possible so we can clear that the fault as quick as possible well there's no engineering design there's no formula this code just simply says do it this way if you follow the code if you size the wires according to these methods and if you terminate them according this methods it's going to provide the practical application that you need they clear that fault quick enough to make sure that it is safe so we make sure we have an effective ground fault current path very important we comply with the code that we understand what a system bonding jumper is and we understand what a supply say by the jumpers that we understand wanted equipment grounding conductors we understand article 2 feet completely nothing is more important than that to make sure that we make an installation safe so that's kind of like some basics and let's go a little further let me continue on the equipment grounding conductor an example you must bring an equipment grounding conductor to every single circuit every single time there is no condition that we don't and so if you had a parking lot light outside then you'd bring in equipment grounding conductor and you would terminate it to the equipment grounding terminal of that pole now it is a common practice around the country at places that they drive ground rods at poles and if anybody knows me and knows that I think I'm thinking this is nuts that anybody would drive a ground rod at a pole and if you're watching this DVD you don't understand why I think it's nuts then you need to get the grounding amount of DVD to have a better understanding grounding does not do anything to make anything safe from an electrical fault condition let me repeat that you drive a ground it will never make it safe it doesn't do anything in the event you have an equipment grounding you have a fault to a metal enclosure the only way you can make it safe let me go back let's look at this graphic the only way to make it safe is to do what bring have an effective ground fault current path from the point of a fault back over to the source that is all you have there is no other option you don't drive ground rods to make something say I didn't know that domain when I was younger and I was teaching the class of when I was reading the books all the books talked about grounding total complete BS so you do not drive a ground right at a pole is it illegal no it's not illegal the code doesn't care to 50/50 for calls that an axillary electrode you can drive a ground rod it can be eight feet four feet two feet you don't have to have a ground rod you can run six gauge wire to it you can run cat five wire to it it doesn't really matter because it's not required my concern about it is that some people might think the ground rod somehow provides some kind of safe I've heard arguments for reasons why a ground rod now here's the things but here's what happens if you have a ground rod and you have no equipment grounding conductor which is a practice it is a thought and you have a fault fault current will come to the pole from the conductor and it's only path is returned back to the earth if the ground resistance was 25 ohms if that were the case and if the source is 120 then the current traveling through that circuit would only be four point eight amps you're not going to clear a fault so looking at this graphic yes if you have a ground rod it will carry current 4.8 amps if it were 25 ohms at 120 volts but what it doesn't do is it does not room remove dangerous touch and contact voltage let me repeat this if you drop a ground rod you're not going to clear fault you will have a bolt this gradient the earth that will kill you and there's nothing that you can do about that so now take a look at this photo here this is a Miami a bunch of guys driving this very very difficult ground rod into the earth there because it's coral rock in Miami that actually that was near coral a care of Coral Gables so obviously they call that city Coral Gables for some reason and now people argue with Mike the reason you have a ground rod is for lightning protection if anybody's saying that could you obviously don't know lightning protection if you said that so let's just start right there you're just like related protection because you don't know what you're talking about okay lightning protection means that you're protecting something and if you're going to protect something you're protecting it according to a standard the standard is NFPA 780 okay which is the national lightning prison and the national person NFPA lightning lightning protection lightning put against lightning protection NFPA 780 lightning Petryk see if we get a right title or not I'm missing the title there for some reason NFPA seven a lightning protection I guess lightning protection lightning protection systems okay lightning protection substantive insulation lady put eight seven eighty if you're trying to protect something you means you're trying to protect it I have a house I'm just building a barn right now I have lightning protection on my house and on my bike my remote garage why I don't want my house on my remote garage to burn down in the event of a lightning strike so I put air terminals on that to capture that and the divert that away if you have a pole outside if you're saying well I want to protect the pole and you put a ground rod at the bottom of the pole and the lightning take a look at this graphic here that bolt of lightning goes right through that pole if you think driving a ground rod at the bottom of the pole is going to protect the ballast or the fixture on the top of the pole then we got a problem here because that's not how it works you don't drive something at the bottom of something thinking that you're protected if that were the case then go get ahold of NASA and tell them listen you guys are putting these three large towers around the launch pad so that lightning doesn't hit the launch pad or you got to do is drive the ground right on the bottom and connect it to the bottom of the rocket you protect the whole rocket did I make any sense the heck would you drive a grommet at the bottom of a pole okay I got it relax so here's a great one it's my last one and I'll stop going nuts let me see if I understand something we got 150 foot pole we got these anchor bolts that are probably 15 feet in the concrete with a huge concrete cage we got at least what 12 huge bolts in the and we have this cute muted wired it comes down the probably goes nowhere are you kidding me I don't think you understand how this whole thing works you need to make sure you make it safe what I have to do bring in equipment grounding conductor connect it back properly terminate every single thing your equipment route your wire nuts your terminations they need to be like rock-solid back to the source in the event of a fault what open up a protective device have a low impedance path follow the code and we're going to protect people so that's my story any of your comments before we get to that just one I think that that whole series right there with the streetlight would also be very effective ish instead of the street light there were a process computer machine tools they drive ground rods machine tool there are you kidding me the heck you want drive around machine tool but we'll talk about that well not in this class because it's not grounding yeah but the reason I say process computers is there's a Satan chemical plant so you have this for in especially in the 80s 90s there was this thing called well you have to have an isolated ground for our process computer and you have the same exact situation as you do with the streetlights every wall drive ground rods isolated ground circuits and equipment and somehow right crazy I don't want to get into all that is there anything I said that we could add to that part yeah I'm just going to mention real fast maybe we can send a newsletter on this I just I sent you the actual original study on the shock effects on humans that Charles dazzl did at UC Cal Berkeley and you know it shows the pictures of the tests and people getting zapped and then we'll send that as a newsletter yeah I've had it for many many years I've had a lot of old stops of great archive stop that I say it's something eyes did in the 60s and back in the 40s great great engineering work human test subjects

Channel: MikeHoltNEC

Views: 237,767

Keywords: grounding, bonding, electric, saftey, NEC, 2014, Article 250, shock, ground, pool, home, swimming pool, marina, ohm, Electric Shock (Disease Cause)

Id: 3vvvv5QVZoA

Length: 26min 25sec (1585 seconds)

Published: Thu Oct 31 2013