Ground Resistance Measurement 250.53(A)(2) (26min:27sec)

what we're going to do today is we're going to go ahead and test grounding you can see how hard this ground is my earth is right here by the way this is my office where I work at and you'll see the background and what we're gonna do is we're in the dr ground rods down actually we have a whole bunch of ground rods we're going to coupling them together we have the proper equipment right here to be able to driving them down every five feet we're going to drive the ground rod down we're going to do a three pole fault potential method and what kind of talk about the equipment here we're going to use a clamp-on meter to check the ground at the same time we're going to be using an ant meter to measure the current flow in the event of a ground fault we're going to take a volt meter and also test the touch potential so we're going to do is we're going to introduce you to my helper actually going to help raise been with utility companies or electric utilities right Joe for 29 years and my background with electrical and Joe the Simms background with the electric utilities and let's take a look at some of the equipment that we're going to be using here right Mike well we have a clamp on grounding tester made by AEMC which requires no other things other than just to clamp it on we have a couple of meters there to do our amperage readings we have our safety equipment hats gloves of our ground rods and assorted other small tools okay now we're going to perform our tests what I'd like to show you what we have is right now a ten-foot ground rod that's standing up it's tied on to a ground rod that's 10 foot already driven in the earth actually I'm in danger right now think about it we have two meters that we're checking on the right-hand side is going to be the amp meter will try to keep that consistent on the left-hand side is going to be the volt meter we see the voltage is about 105 volts and the average is about 0.4 or 4 tenths of a millimeter now let's see where this current is coming from if you take a look here we have an extension cord with 110 volts it continues over here it's energizing this rod this rod is 110 volts voltage is going down to the earth I have the current clamp right on here that's connected over to the amp meter so we have four tenths of an amp Joe going directly to the earth at a hundred and twenty volts I have the leads of the voltmeter connected to the ground rod and then I have the other lead of the voltmeter directly to the earth and when I did that that's when we had about 105 volts I'm going to go back onto the ground rod and I'm going to take this only about a foot away and stick the one lead into the earth the red lead the black lead is on to the ground rod which is 120 volts and that gives me about a hundred and four volts so if I'm only a foot away I have a hundred and four volts which has a differential so that's a difference of potential so if my knee is on the earth right here like I'm standing and if I touch this ground rod the difference of potential between this ground rod which is energized and me is a hundred and four volts all right now what I'm going to have you do and I got to be careful here will turn this power off here right now is Joe you're going to check the resistance using the three-point and you're going to use the resistance measurement also with the clamp on so we'll go ahead and get that next okay now we're going to do our two resistance measurements the first one we're going to do is with the AEMC 37:10 clamp-on ammeter which this meter has both the transmitter and receiver in it it transmits a signal back out through the system neutral to the power company into the ground back through the ground and up this conductor or grounding electrode and the meter takes a reading no so much energy it sends out it knows what frequency it sends it out at it looks for that information to come back and makes its measurements so we're all set up we're hooked back to system neutral we'll go ahead and get our meter turned on and we will clamp on and take our first reading with this type of equipment the one thing you have to do is always make sure your CTS are clean can you touch the side to the CT to the rod does that have an effect or not well I always say is with most CTS that you try to keep it in the middle got it we've got the meter zeroed in and it's stabilized and giving us a reading of 265 ohms this is at 10 foot into the earth all right so now we're going to go ahead and use a three-point method right the next thing we do is a three-point fall potential okay and we will hook up our three-point fall potential well disconnect this from the system neutral exactly we need just a bear rod so when you use a three-point method you can only use that one rod not connected to anything that's correct okay so we have now we now have our connection to the rod with a three-point follow potential we at some distance out in the fielder we have one second you had one probe which was the current probe it's the farthest one and you had that at what distance it's at 170 feet and then we have the potential probe at 62% of that which was somewhere like around 107 or something else we Ramirez check that out to make sure that right okay so now we're taking the 10-foot resistance of this ground rod only not connected anything else using a 62% method which is also called a three-point method and it's the fall of potential method so there are three different terms of use sometimes we have a stick we've put our own references in the field now we're not using a digital meter this is just simply a method that could be used it's either digital or non digital this is just an older type right so now what we'll do is we'll also transmit a signal of a known energy level and see what we come up with so I'll just move it off a little bit here so we can sweep it in so we're taking the bridge and bringing it back to zero this method obviously is not as fast as a clamp-on but it's still an accurate method okay now we on the multiplier scale of a thousand we're reading point three eight so that's 380 ohms through this method okay the clamp on I'm writing it down was 265 the three point method was three what 383 80 ohms now it's not uncommon that both these methods don't match because we're using different distances through the soil back to our references and they're using different techniques different techniques hmm 360 380 versus 265 I guess if I'm looking to get a low resistance and I was going to buy a meter I'd buy to me that it's going to give me the lowest resistance well the one thing we want to keep in mind here this is one rod we're only ten feet in the ground so as we go deeper it might change yes it's going to be low okay let's see what happens on the next Mary so let's go ahead and go 20 feet down okay all right so now we got probably at 20 Peter now 20 feed me ground okay let me set this on here and we'll drive this down on it and then I'll give us it what we use in our reference point a nice place to clamp on there okay I run you know give you a rib to you okay 420 mills 410 Sonia wouldn't hit before same thing is before we had four cents of an animal fortunes so we're now 20 feet we just went up a hundredth of them no trial practice something so we didn't change the current flow at all don't be interesting to see what the resistance is angry let's check it out and now we're down at 20 feet you connected a neutral connect to neutral use your clamp meter use a clamp meter now last time we make my notes here I'm not gonna tell you what we had last time that we had on hand fluent you okay we're going to stabilize out at about 240 ohms 240 ohms I mean the resistance went from 265 from 10 feet down to 240 at 20 feet the current for all practical purposes didn't change at all okay so now we got to check the three points see if that changes last time it was 380 let's see if it stays close to that we are at what's absolutely 300 ohms on the three-point follow potential 300 ohms okay dropped a little air - I surprised me because I thought if we did if we double the resistance in the ground we would have significantly reduced that resistance I I'm not surprised on the current flow I didn't think the ground rod depth would affect the current whoa you take 120 volts directly to the earth at 20 feet you draw four tenths of an amp you're never going to trip a breaker right at ten feet with four tenths of an ampere resistance went down a little bit but we're nowhere near work we're still over 200 ohms at 20 feet we're nowhere near the 25 ohms of the code you know encouraged us to get to right all right we're gonna go down to 30 feet but that was pretty tough on the drive yeah that was hard I thought I would have thought the resistance to dropped a little bit more based on the compactness of the earth all right let's do 30 feet okay I said I really hope that we can we can drop this this goes down a little easier because that was really hard okay I'll put my head down cuz you don't me to get any shavings and head down head down let's go let me get that there is a better way it's a driver that's mounted on a truck yeah it has a big slide on I thought that's what you were brand oh yeah they get all over the top because that's going to be the place that we're going to use it I'm saying that's it once we good now you can appreciate why it cost so much to for somebody to come out and drive grounds yeah really cuz you run into the unknowns and it takes a while to do it I would only pay them by the ohm what we have right here is we have a ground rod that we've drove already a little earlier this morning and that's 50 feet we're going to check the ground resistance on that using the clamp on meter and when we're going to final finish up the other ground right on the other side which is down to 30 feet we're just about given up on that one because that one hit some really hard lime rock or something in the earth we're going to measure that ground resistance and then we're going to time together and we're going to find out and Joe what do you figure they're probably 75 feet apart 60 feet apart so we're going to find if we put two ground rods 150 foot we'll find out what the resistance of this one is the other one 30 foot deep find out what the resistance of that put them in parallel and find out what's a total resistance how does that work out so we're going to go ahead and finish up and then we'll see what happens all right we're down to 30 feet tough 30 feet okay you're going to put it in a hundred ten volts okay I got my ammeter set to AC put it in the little hole whew man our current went up to 1.3 amps I mean not a whole lot but I mean it's more than 0.4 so 1.3 amperes and now we're going to check the clamp on meter and a three Pole three point okay now we started at 10 feet 265 20 feet 240 but the amperages did not change now at 30 feet the amperage went to 1.3 which means I would think that amperage was going to go down to 80 amps or yeah I think it's going to go down at least below 100 okay we're at 60 and stabilizes 68 ohms okay I mean ohms alright three point method I'll set this to a hundred and I'm gonna set this around 70 this conductors not actually this is a little higher what I must set it right there see how it goes this get you started okay three point three point has been high so I'm guessing this is gonna be close to like a hundred ohms am I good or what yeah one hundred dollars one hundred of the three point six eight ohms on the clamp one point three amperes on the current flow you think we can go forty feet or no we got that the other ground ride we drove fifty feet you want to just use that one for fifty feet to find out what we get at fifty feet there I think we can go another ten V alright we'll try one more ten feet look at it yeah I think I think if you were to put another one on you'd have that same hard spot and then you'd go through like you say run your coupling through the library yeah but wouldn't you think the couplings would have broken the line the first a second a third time I would have thought so but all right let's do our testing here okay what's on DC okay I set that ten on AC little hole whoa whoa now we're up there we are 5.6 basically 5.6 amps with my little calculator if that were true the resistance then our being a over I then 120 divided by about 5.6 should give us a resistance of around 21 ohms well 22.5 you know what looks like there's a correlation between those resistance in this current flow alright so now we go with a three-point method the three point methods been around 25% higher than the clamp on which means if I'm going to predict this I'm going to predict this on the on the three point method we're going to be around 30 ohms okay so we got a 25 ohms didn't we yeah they something on the on the clamp on by going 40 feet can try rock it back and we'll go the other way huh No you're trying to get any other sign huh well how about 10 what a racket back from 10 No so basically using a meter like this that's going to be more analog we get down those lower resistances it's really not going to you have to go to a digital you're least in this vintage of equipment right yeah so you're gonna have to go to a digital three point method that meter right I'm sure would work much more accurately than this but up to this point this has been a good yeah if anybody close all right well we can't check with here so we're gonna look like the clamp we can use the clamp as a basis now what I'd like to do we're going to go 50 feet yeah let's try all right Cody okay fifty feet I never would have expected that it was a hard 50 it was a hard 50 Wow 8.1 amperes that's looking good all right so now 50 feet we have 8.1 amperes I would expect the resistance to be around 15 ohms on the clamp meter now let's check that now I'm guessing machismo Ohm's law formula R is eagle-eye 120 over I of 8.11 mathematically it's a it's 15 ohms and mathematically that's been really close so I'm gonna say around 16 ohms 15 to 16 we come up with 16.4 1 16.4 ohms alright so we have 50 feet we have 8.1 amperes going to ground at 120 volts and we have 16 point 4 ohms which means that relationship with Ohm's law works so what I could do is instead of me actually using these meters I could drive a ground where I take 120 volts measure the current calculate out the resistance that way right yeah the danger is though you're dealing with 120 volts you can get killed which you don't want to do right so either one of these two meters are going to work pretty much effectively I kind of like that clamp on me to go oh yes all around that's just hard to beat that meter yeah all right let's put them a parallel ok mutual is on and you're going to check that ground resistance using the clamp meter on that side yes this side is a higher resistance of the other side okay this is a West ground it's the West ground at 50 feet we're 21.7 hey let's take 120 volts to that and see what the amperage is on that okay okay and Rigo powers on so we got 120 volts there I'm going to say it's going to draw about six amperes is five point seven four we have two ground rods in parallel and the resistance on the west side right here is twenty-one point seven ohms and the resistance on the other side was sixteen point four and the current flow is five point seven here in 8.11 on the east side so let's see what happens to the current flow if we add them together you ready one two three powers on the total current came out to be 13 amperes which was right and the resistance is somewhere like around 10 ohms and the actual reading is 10.8 10.8 ohms so there's anything else we need to check here well one other thing I would like to do just for sake of testing and that is to bring out our calibrator and we'll pick 12.4 own resistance point here and see how close they can do one last check okay that was twelve point four and came out to be twelve point six we're at twelve point six alright so equipment checks out there's only one thing I want to do and that is that what is a touch potential using the ground only with an open nutritive service so if we already have everything set here all I'm going to do is I'm going to lift the neutral okay when I lift the neutral I'm going to take one load on I use a hair dryer on and see what happens to touch potential with the one ground rod and with two ground rods okay okay let me get the hairdryer okay what I have here is I have PVC coming in two hots in a neutral or grounded conductor this neutral is bonded over to this equipment grounding and I'm going to disconnect my neutral I'm going to make sure my neutrals and my grounds power is off jopie give me a screwdriver there maybe it's on top here my neutrals and grounds I'll make sure the tied together and what I have is I have all the circuit breakers off but one and I have a hairdryer and what I'll do is I turn on the one load so we have 120 volts coming off the circuit going to the receptacle right here that goes over to the hairdryer the voltage and the current continues and returns back to the hairdryer on the neutral gets back to the neutral but since it's lost the return path it connects over to the ground and what we have now the ground is connected to the case which is connected to the metal structure of this building here I'm going to have touch potential and I want to find out is if it's properly grounded what's a touch potential with two ground rods like we have the 250-foot ground rods or one round rod and what that value is going to come out to be so we'll check that out in a second let's get the right circuits okay Joe go ahead and turn on the hairdryer 1800 watt hairdryer right trigger on speed go ahead alright if we take a look at the voltage here we're operating at about 8 volts which is this metal parts of the earth go ahead and turn it on the other speed now we jump up to 20 volts so we lose a neutral the metal parts of all the building becomes energized relative to the earth all right let's cut one of the grounds off and see what happens we have one ground rod at 21 ohms our voltage is fifteen point eight where before it was lower than that and now go to the other speed now we're going over 30 I think it was 24 so as we reduce the earth resistance and you lose a neutral the touch potential increases so we really want to have a good ground a very low resistive ground because it does provide a reduction test potential okay let me summarize what we've done here Joe looks to me like when we went to 10 feet we had like around 300 ohms 20 feet 300 ohms the current traveling to ground direct on a 20 volt to that ground rod was about a half an amp you're actually four tenths of an ampere we had the touch potential was still 120 volts you could get killed even we had a ground rod that's not going to solve it went to 30 feet we started dropping down to 1.3 amperes and that resistance went down close to anywhere between 68 and hundred ohms depending upon the meters that you use let's say around 75 ohms or so we went to 40 feet that's one where there's a big drop down the resistance went down below 25 ohms right but a current was still only five point six amperes which is basically works out that Ohm's law I is equal to e over R 120 over the resistance we got down to 50 feet we dropped down some more resistance down the 16 ohms which was pretty good our current went up to eight point 11 and then we had two ground rods to East Side which was 16 ohms the west side which 50 feet which was 21 ohms we put them in parallel that resistance went down to 10 point 8 ohms again I'm really surprised really surprised and I didn't think the clamp on round resistant measurement could possibly work I really didn't and I thought the three point method I thought that whole thing was a little spooky anyhow I thought you know that was a little work well there is some limitations then upon what direction you go yeah I mean just oil resistivity and everything but bottom line it looks like you know you could put an amp meter on there take 120 volts measure the current figure out that resistance right but it's too dangerous okay so if you used a three-point method or if you use the clamp method either ones fine and then a matter of magus convenience if you could afford the clamp-on and you don't need to test it that often in that variety of them you only need to do a few ground tests the three point method would be fine if you have the time in the space if you're not limited by concrete and asphalt that's right and inside of a building and you did there's no there's only one way to go I see just saying if you're trying to measure ground right in the building yeah I've run into that a lot or you have a yard it's only 75 by a hundred exactly yeah there's right so multiple work fine and it's just a matter of cost convenience and features time and time anytime is a big practice take it takes a lot of time three point four attention okay touch will tend to reduce when we had better grounds yes a little but we still didn't trip a breaker no we had 250-foot ground rods tied together we only drew I think it was about thirteen point two four amperes right well I think that's it for now we're done guys we'll see what happens in the future stay tuned you

Channel: MikeHoltNEC

Views: 306,863

Rating: 4.82793 out of 5

Keywords: grounding rod, experiment, real world, resistance, testing, utility, 3 pole fault potential method, clamp, electric, fault

Id: Yg6G5VUSsWA

Length: 26min 26sec (1586 seconds)

Published: Mon Feb 24 2014