Ground Resistance Measurement, NEC 2014 - [250.53(A)(2)], (26min:27sec) 

Mike Holt is a true legend. I have learned so much from your videos. Thank you and god bless.

I would love to see a follow-up video that incorporates the water line and how that plays into the grounding. Most homes in Mt area used the water line as the original grounding.

This is a really great video covering the The Grounding System (G.S.). G.S. is a science of it's own. Many people (that's in reference to electricians) don't realize the importance of the ground. I am a retired electrician and came across many instances where the G.S.was shoddy as all get out. Don't get me wrong, I also saw many, many well installed G.S. too. Any way, the G.S. is what helps make your electrical system safe. When a new trainee or a journeyman came along and would ask which wires were the most important, I explained the G.S. wire is THE important wire (system).

You can tell that Mike's not just book smart but has actually done some work in the field

I would be most interested in the resistance of 50 ft of #4 solid bare copper in an 18” deep trench vs your 50 ft straight down deep ground rod in the same location. We have achieved better lightning protection and lower resistance with long trench bare copper . It seems particularly good for suppression of building to building transients from nearby lightning. So much so - that now it is our standard practice to add bare copper to any excavation trenching and to underground concrete (Ufer Ground) all tied to the main service entrance ground rod(s).

Great video! Thanks to you guys for performing these tests. The reason I even stumbled upon this video is because I am trying to learn how the plastic moisture membrane between the poured on grade concrete slab will affect the use of a Ufer type ground system. I will continue my search.

"Still didn't trip a breaker- we'll see what the future holds" GFCI breakers nowadays because of this man🤣

Thanks a lot for this educative lesson, but what is the formulas for calculating both EARTH and GROUND resistances ?

Its interesting that 25 Ohms is allowed in the US. In Hungary the ground rod contact resistance must be under 10 Ohms even in the worst conditions(dry soil in summer, frozen soil in winter, rocky soil). The soil is usually good here and 2 pieces of 2 meter long ground rods at least 2 meters apart from each other is already inder 5 Ohms. Small houses have single phase 230 V 32 A serivces, larger houses have 230/400 V 3 phase 25 or 32 A. Higher services are possible but usually not needed because most houses use gas or wood stoves for heating. The gas pipes must be bonded to the ground in the panel.

This is the first Mike Holt video I've watched and I cannot express how happy I am to have stumbled upon it. I've been looking for videos on grounding electrodes testing, megger process etc. We've had over 20 instances of lightning damage on low voltage 2 wire irrigation systems. I've been watching your videos all week, the grounding and bonding video last few days. I cannot thank you enough for sharing your hard earned knowledge. You are saving lives.

What electrical standards this earth clamp-on test procedure belongs to?

Were wrong saying "elec. current will always take the path of least resistance to ground" Actually it takes the path of least resistance to its source.

I love your videos and have watched them all. Congratulations on your knowledge and ability to teach. I've learned an awful lot from you. As a radio amateur, I had many, many doubts about grounding. Now, after watching your videos, I have finally understood what I have to do to properly ground my station. Keep up with the good work. Thanks from Brazil.

Wish you could explain bit more detail in relationship to stray tingle voltage on farms.....four legged creatures standing on the ground getting say 4v shock from water in a plugged in heated water bucket even with main power switch off.

Looks like you guys got alot of sand in florida. Where does the current go? If it takes that much depth to get your proper resistance, then how in the world can the nec say you're automatically good by having 2 of them driven 8 feet deep 6 feet apart?

It seems to me..the resistance of grounding electrodes isn't low enough to trip the breaker..why do we use them??Why don't we use only the neutral and branch circuit grounding conductors for the return path back to the source.

Thank you for the information. The 25 ohms the NEC requires and two ground rods 8 Ft. apart I never seen how it worked. Up here in Alaska we have a lot of ground water and you can in wet years meet that but now that we have not had good rains never happens. I once worked on an explosive storage bunker and the government (ARMY CORPS) required 50ft. Rods like you installed and every 25ft. around the bunker. This took a long time for two of us and 500 MCM ground loop cad welded to the rods.Kent

"if I was having someone install ground rods, I'd pay by the ohm" hahaha, love ya mike

With the clamp on method you can reduce the safety issue if you put a 3/4" pc. of pvc sleeve over the exposed rod then bond the wire to the rod followed by a piece of say 2" pvc that extends beyond the top of the electrode. Next. Put your clamp around the 3/4" pvc. Now this the part I get a kick out of, stick that piece of wire into the receptacle...classic..Now turn on the power...classic..thanks!

Thank you so much, that was so helpful I wonder how long the ground would be for land with so close surface water. about 9 feet and how many ground rods I need to neutralize 1. 30 A of 230V , 2. 40KV of 1mA.

I am curious what the depth to ground water is at the site. Perhaps it would greatly influence resistance.

Thank you Mike , this video help me understand a lot. every electrician must watch the video.

Thanks for the great knowledge you are passing down, I have watched most of your videos and they are the best source out there!

Great demonstration video on grounding and measurement techniques! (One an advanced electrician, from Hungary)

Thanks for the video. There have been some wild electrical issues in my area. Got some UPS's installed for all the sensitive equipment, but realize the ground is bonded to the water pipe in the house... and not only that, but it's super corroded. Definitely going to be getting a clean ground installed to two 8 ft grounding rods. I live in a kind of half collapsed area economically so no tradespeople are available.. have to do it myself. Thanks for the video, it makes it easier to conceptualize and to install everything properly. I think this will actually help my neighbors as well, since there is just a lot of weird grounding going on that is causing power surges... or something. We got hit with one so bad It fried half the LCOS on my car dash... scared the shit out of me. Thought it was EMP or something, but.. who knows. Weird area. Just hope these new rods will fix some of the issues.

Excellent demonstration. With all the rocks in Tennessee, it would be virtually impossible to drive a rod 50’ deep.

I LOVE this video and would like to thank Mike Holt for producing it. As always, here comes the "but". i have two comments that i'd like to make on this video. I recently asked the inspector in our local area about the exact method that you're using it this video, if simply using Ohm's law and applying the 120v to an isolated grounding electrode would be permissible. I specifically requested using a 5A non-time delay fuse and seeing if it would blow that fuse, and he said that he couldn't understand why not. So i've been doing a little research into this. My two comments/questions on this GREAT video would be: 1) We are not actually testing for resistance to the Earth as static and lighting would think of finding it's way "to the Earth", but we are actually testing resistance from our grounding electrode to the utility company's grounding electrode system THROUGH the earth. that applied voltage of 120v is simply trying to find its way back to it's source, the transformer from which it is derived. so technically speaking , we could improve our resistance to this test by improving the grounding electrode at the transformer just as well as the one on our system. but then again, we're not really testing our resistance "to the earth," we're improving our resistance between 2 grounding electrodes THROUGH the earth. 2) if this testing method is acceptable (as i really don't know a practical point to measure "the earth" from), why would we buy the expensive testers if a simple 120v application and a simple R = E/I calculation can be done? or much less, a 50-cent 5A glass fuse could be used? I think the point made in the video of 120v being too dangerous to handle is a moot point, as we are professionals and should be able to safely manipulate 120v. Thank you in advance for your thoughts.

Excellent video. Suppose got I enough grounding rod in the ground to get to 20 OHMS of resistance, Would this much improved ground have an effect on flickering LED bulbs when my mini split is running ? 48K ACIQ 48Z-HH-M5 (220 volt Inverter) Meaning eliminate the flickering ? Appreciate your help here.

i just did yesterday the dangerous method mentionned by mike, this video was really enlightning, bc we have 230v i got like 1-2amp range for a 4 feet deep rod i guess i understand why TT is popular around here, only utility grid people who use TN-C actually dig a deep rod for their transformers

Excellent topic.Well presented too. Seems though there is a good case to offer gfi at the mains input though.Standard in Europe nowadays. Many thanks.Learned a lot.

Great job Mike.....you are a rockstar in the electrical world.....I will use this vid to teach the linesmen at work....... thumbs up man!!!!!

You said that the better grounding reduces the touch potential which is true but even with 2 at 50' it does not really protect you because the hair dryer is a tiny load. If you were running a space heater and a fridge on the same line (L1 vs L2) your touch potential would probably be close to 100volts as this circuit is basically a voltage divider. Another way to look at it is if you have an unbalanced load over 13 amps then the entire voltage drop will result from the ground rod resistance so 120V at the ground rod. Also, I wonder how deep the ground rod at the poll has been driven because it contributes to your resistance.

Depends on the conductivity of the soil. Come up to Connecticut where the state flower is the rock!

You do a good job

What if one uses the Uffer ground (concrete-encased electrode, the foundation rebar network). You can break a little concrete, find the rebar, grind the rust, install a #4 CU solid with approved clamp, use a little fast concrete to patch the foundation hole. Does the foundation rebar have lower resistance to the ground compared to the 50' and 30' ground rods? If so, it would trip the breaker.

Howdy. Absolutely wonderful clip. As I see it. A low soil resistance facilitates shock protection by increasing the fault current and thus speeding up the breaker triggering. Another approach would be Encirclement of the Environment of Utilization (house). This would facilitate shock protection by Potential Equilization in the fault environment. High regards.

Excellent demonstration. Thank you.

Sir, In the last experiment of touch potential if we reduce the earth resistance (in case of Loss Neutral) the touch potential rise . Than if touch potential rise than it is not safe ...

Try coming over Hawaii (Hawaii island) and trying that test on the Kona side. I guarantee you every technique, method, depth, distance, measurements and etc. will be entirely different. Bring your WHEATIES! The reason I’m interested in your results would be because of the earths composition. Our land is basically lava rock, high in iron content. Diving a ground rod 8’ is nearly impossible w/o predrilling a hole first. My point is that 50’ or six inch’s. The 8’ code is a myth.

Mike - what was the coupling method between rods when you added extension rods? No CADWELD?

Thank you very much for sharing this valuable information.

Truly outstanding information. Thank you!

Very informative videos Mike. Just a query, i noticed at 19:25, current draw from the induced voltage on the rod was 5.75mA and not Amps. Can you verify that value please. Am interested to know why such high current draw without a known load and what work is being done by the power evidently present in the circuit.

I was taught to install multiple rods minimum 6' apart to achieve 25 ohms or less. I have never seen rod extensions. I am generally in California clay.

Amazing video!! Thank you for this explanation!

Very good video thank you. I would like to ask a question, the resistance is 25 ohms max but what is the distance? For instance you had two different ground rods installed one started at 50 feet deep and the other was starting at 10 feet what was the distance for each rod to the common measurement ground, which I assume was located near your electrical panel. This could account for the different measurements for the two rods. I am no expert on this but it would seem to me that it would be better to measure the voltage drop over a specified distance. A 25 ohm per foot spec would make more sense to me. In addition since the stance of a man would be about 3 feet measuring from each foot (a wide stance for maximum voltage between each foot) would be a good measurement reference to use. This would be very important for a touch potential that you did start to address in your video. Here the ground rod at you electrical panels resistance would be more important for touch potential to your building. Lighting is a different beast all together as the current here can be 100,000 amps or even more. So much for the 25 ohms spec when it comes to lighting. Protection from lighting can only be accomplished by a Faraday cage. How ever getting back to it, adding a distance would add more meaning in my opinion to the 25 ohms max since with out it we could be measuring over 3 feet to 3 miles. Were as one would most likely would pass and the other would probably fail. On top of that there is soil conditions. Wet versus dry. Since you had to go down 50 feet it seems to me that your soil was very dry at the time of your test. I would have like to have seen what change would have happened if you had poured water over the ground rod. The soil's mineral content is also a factor in addition to other factors. There are so many variables that the 25 ohm max spec by itself does not seem to be adequate. Ideally one would want to have a radial pattern of ground lines spreading out from the ground rod. This is what is done with cathodic protection for pipe lines and AM radio stations ground plane. Here, in both cases, grounding is spread over a large area. This of course is not practical for electrical work.

excellent guys .... most informative video ... came here searching for lightening system ground resistance n found out this ...

Mike first time in 30 years I've seen you in work boots, go scuff em up a little!! Enjoyed the video, Your Indy Instructor Mike Fox.

When use clamp-on in TT system how can the device transmit the signal? Because there's no connection between neutral and ground in the load side.

Many Thanks, what if I want to ground a high voltage power supply of 20 and 40 KV of 300w and 120V respectively ? can I use many rods of lower depth instead of just one like yours

Wouldn't the current showing on the meter depend on the distance from the Ground r\Rod?

Sir ,during touch potential experiment ,the following is the sequence shown: 1) 1st with two ground 2) 2nd test with single ground rod. Am i correct...

Great video. I've heard that current can travel with almost no resistance through the earth, that is, once you get it past the resistance of getting it into the earth. It would take men like you to prove or disprove such a thing please do

i have used assoc research three point method for ( we have four units like this and two clamp ons ) thirty plkus years and the results are good. we cant use the clamp on for isolated ground rods etc . resusts are eroneus .

Great experiment.! Thank you, guys.

Can you please explain what the dangers are in this experiment with respect to the amperage. I'm new to electricity.

Great seeing Mike estimate that math on the fly. The more you do that the better you get at a general math estimate. Obviously Mike does this multiple times a day for the last couple decades. But that is just an estimate of course.

Can not comprehend without a schematic drawing!

Excellent description and examples

I just watched your youtube video "Grounding-Ground Resistance Measurement" 26min:27 sec published 2/24/14. I found it very educational but one thing left me confused. At 13:26 into the video where you were reading the resistance meter with it's dial at "1" and the scale multipier at "1000" you said it was 100 ohms. Whatam I missing? That would be 1000 ohms wouldn't it?

I really appreciate the videos Mike, also appreciate the jokes in this particular video hahaha good way to keep it fun 😄

Is the fluke meter set to milli amps

hi can you help me i have a fluke 1625 ground tester and we don't know if we are doing the things rigth

"Looks like there is a relation between the resistance and this current flow" - uses ohms *law* to calculate... :) It's a great video, just busting some chops.

What precautions did you guys take to safely short-circuit the neutral to the premises grounding electrode? The danger would have been if you made contact with the neutral lead while standing on the ground it would have made a circuit between you and the grounding electrode at the system transformer, correct?

Dont you mean 120 volts A.C.???

would the diameter size of the rod to the next diameter make a difference and also the type of material , can you try a galvanized or stainless steel . yes the price is a factor when driving 50 feet of rod

I have a feeling that the ground rod went into the ground in an angle (not vertically), reaching a lesser depth elevation than the sum of the electrodes' height. The depth elevation -- measured vertically -- makes a bigger difference than the combined length of the grounding electrode.

Question sir, During drilling rod is getting hot right? is there any effect in the ohms reading while hot?

Question: Can a person who has ZERO ground in a house, ground just ONE power outlet in the house by running a ground wire from the ground terminal out into a grounded stake in the ground? My house has old screw in fuses, and absolutely no ground wire anywhere. There's no plumbing or anything in the house to use for a ground either. I run a compost toilet/outhouse, and haul water there. I want to avoid the risk of frying my electronics but I cannot afford a full electrical update. It's 10,000-12,000 to do this (almost as much as I PAID for the house!!)... I won't be able to afford it for YEARS best case. SO what I want to do, is somehow protect my electronics by at least grounding ONE outlet cheaply. Is this possible? AND NO, I DO NOT HAVE INSURANCE, so I don't care if things are certified insurable, just so long as my gear is safe.

I fail to understand which exactly, is the resistance their trying to measure. is it the close loop resistance from the grounding? as in, the grounding metal mass in a grounding system is technically open and the only thing connecting it is the ground. is it that?

How are you connecting the ground rods together so you have a solid connection?

Great instructional work, thank you.

Damn Mike looking young

Does reducing earths resistance, increase or decrease the touch potential? "As we reduced the earth resistance and you lose a neutral, the touch potential increases"So we really want to have a good ground, a very low resistance ground, because it does provide a reduction in touch potential"

Nice informative and effort full video :)

Sorry but if Joe is using the clamp on method with just one ground electrode instead of multiple electrodes/grounding points, it is incorrect use of the clamp. You can't use the clamp on method on a single ground point. This is because there is no return path (close loop) for the current on that electrode.

Excelente video

Best explanation

Mike did you say that wrong at 23:07 ... Shouldn't it be, as you lose the earth conductance the touch potential goes up. Less resistance = better conductance to ground = less touch potential...

So why was the ammeter reading in milliamps? Look at 14:50. It is clearly 5.6mA on the meter, yet he is saying it is 5.6A. Since the math works out (Ohm's Law), I can only assume a 1000:1 current transformer has been added off-screen?

So the neutral is being partially replaced by Earth via the ground rods and back to the utility pole ground. Hair dryer wouldn't run otherwise with the neutral removed. Earth being just another conductor even if it's not all that good.

this stuff amazes me. i wish i would have stayed in school

My favorite MH video

Good video but never neglect safety watches rings and shinny things

Y'all hit the water table at 30 feet.

so basically every house that house a single or double grounding rod system that is 8ft down does nothing because if the resistance was checked, all of them would be way over 25 ohms. That's encouraging to know.

the clamp on method is not really suited for isolated ground rod without other parallel paths and readings must be taken on faith, three point fall of potential is accurate on isolated rod etc,

How does this relate to a ufer

Awesome. Mike how come you have time to answer comments, write books, give semminars, study and teach the code, answer emails, and the other millións of thing you do.

Thanks Mike !

👍👍

How deep is the water table?

Flint rock hard to get rod very deep. Thanks

Here in Houston We use a light bulb if the light lights up the ground rod is good.

What a stud!

Has anyone ever seen this type of testing on a concrete encased electrode?

“I would only pay him by the ohm.” Haha

soft ground but a HARD HAT

You can always tell the guys that only learned it in a book and never actually built power line 😂