Electrical question

A week or two ago there was a thread which in it was mentioned installing a earth ground and testing it. I can't get it out of my mind. How do you test a earth ground?

There actually is a special tester that measures the resistance to ground through a ground rod. They happen to be very expensive I am told and I know of no inspectors or businesses that own one although I am sure someone somewhere does. The local standing is that you do not need to drive more than 2 ground rods to make up for the poor grounding capabilities of the ground (if 2 doesn't do it a dozen won't either). So it is cheaper to just drive a second ground rod rather than invest in an expensive tester.

we use 2 different types a vibra-ground tester and a megger to test resistance most utility companies have them ,who ever said there's no need to drive over 2 rods don't know what they are talking about,it depends on the soil types, i've installed a lot of different grounding configurations through the years, in areas were rods can be stacked and driven most of the time you can achieve the reading by driving them deep and getting enough soil contact or hitting soil that will provide a ground, we have used a 90# jack hammer to drive them

At our facility they used a device called a MEGGER to test earth ground integrity. (dont ask me to explain exactly how it operates, its been tooooooo long and Im too busy to look it up lol perhaps others might have the time) We were a Federal US Navy Base and our rules were to drive one earth ground rod and if it failed the megger test to drive another, but if it still failed we werent required to drive a third. Before anyone has a calf Im NOT saying to do that or its right for your area or NEC proper Im ONLY saying those were the rules where I practiced and your area may do it differently

HOWEVER ITS NOTTTTTTTT WHAT MYSELF OR ANY ENGINEERS OR ELECTRICIANS OR LAY PERSONS OR ANY KNOW IT ALL BILLY BOBS SAY THAT MATTERS, ITS WHAT THE LOCAL AUTHORITY SAYS ABOUT THE ESTABLISHMENT AND TESTING AND INTEGRITY OF GROUNDING ELECTRODES THAT MATTERS

If in doubt Id consult the local authority and take a look at the NEC for guidance. While its NOT any legally binding document, its probably more dependable then professional let alone lay opinions rendered here if youre going to bet your life on how to do things...

John T BSEE, JD Tooooooo long retired Electrical Engineer

Thanks everybody. In 1986 I had a mobile home installed on my place and when the utility company installed the meter they told me to install a earth ground rod. Before the day they set the meter I did install one rod as they directed and when they set up my service I was there and nobody tested the rod. After reading the other thread I've been wondering if I've been living without a earth ground. Recently I've learned it really should have had two rods and I was thinking of putting in a second rod so I was hoping I could learn how to test it. Being my second rod 25 years I don't think it would pay to get the tools. I will just ask my utility company to test it the next time they're out here.

In 2005 I built my garage and needed to upgrade my electric service. My electrician was furious with my cable company, as they had strapped on to a conduit for their ground. When I mentioned this to the cable company they said they could not drive their own rod, as it could cause the other rod to lose it's effectiveness, and then I would have no earth ground! I don't understand it, but my electrician agreed, so the cable is strapped to a conduit again!

It wouldnt hurt a thing (even if likely you dont need it) to drive another one and them and the wire and clamp arent all that expensive, for sure cheaper then buying a megger lol

Good luck take care now

John T

Both your and your electrician's BS detectors are
operating properly.

I've seen ground rods tested by connecting them direct to a 120V 15 amp breaker supply.
Sad thing is more often than not the breaker would not trip.
Soil too dry, rod cut off short because it was too "difficult to drive", sandy soil, rocky soil or frozen soil.
Hence one of the reasons for concern when someone starts talking about wiring configurations that run neutral current through the ground system.

The only thing that comes to mind, is that perhaps your cable company guy might have been concerned with, was the possibility of creating a "ground loop", which can become a problem because of a difference in potentials if not properly bonded, and HE stands an excellent chance of creating himself. It happens, and any one worth half of his or her own salt will not deny it. That being said, I don't know if that is what they were suggesting, but that is what comes to mind. As for using your conduits as a ground, that is not a preferred method, but can be a ground IF your conduits are tied together all the way back to your breaker panal, with the bare metal of the conduit in theory touching the bare metal of the panal where they meet, which no doubt has ground tied to it (panal). Again, that is not the preferred method because it depends upon a whole lot of "ifs" and quality metal used, for instance in the made in china conduit that most are using today anyway. That being said, and not knowing if your conduit is grounded or not, no one should ever assume that it is. Conduit generally makes a lousy ground and for obvious reasons, should be avoided. For electronic equipment, I will NOT share a ground with anyone, and generally run my own where possible, or use building structure steel where not. Other than through the power cord, I don't use electrical or telco ground, not will I ever use a conduit. I run my own.

Mark

Mark, good post, I agree BIG TIME I NEVER specified the use of metallic conduit as the equipment grounding conductor, too many places for failure and all the right types of connections and bonds must be used and maybe inexperienced journeymen electricicans were on the job etc etc AND I SAY AND DESIGNED THAT WAY REGARDLESS IF THE LOCAL AUTHORITY OR NEC PERMITTED IT

YES I also agree single point grounding is preferred to reduce ground loop problems

Were again on the same page (as usual) it appears

John T

What Buick said .You run a wire off a breaker {I use 20 amp] and turn it on connected to the rod . Take an amprobe reading off the wire . Now you have volts and amps you can calculate the ohms with simple ohms law math. Yes the breaker does not trip but dumps current into the rod. If it trips you can take a reading off the first few seconds before tripping.

Mornin there Doc, no offense and NOT wanting to argue, just learn (HELP ME AND THE OTHERS OUT HERE IF YOU CAN), You and Buick are gonna have to explain that process to me of your running a hot wire out to the "Grounding Electrode" driven in earth copper rod (which gets bonded to the service Neutral/Ground via a No 4 bare copper "Grounding Electrode Conductor) and connecting the hot wire to that copper rod to measure resistance???????? Resistance of what??? The resistance in that 120 VAC circuit you just made between Hot and Neutral via its bond to the No 4 bare copper "Grounding Electrode" conductor to the "Grounding Electrode" copper rod is veryyyyyyyyyyy veryyyyyyyyyy low ohms (No 4 wire is low resistance between that rod and Neutral) and will pop that breaker almost instantly


Its been years since I was a design engineer and our installation used an expensive Megger to test the integrity of the Grounding Electrode (driven into earth copper rod) and if it didnt pass we were required to drive yet another copper ground rod.....We didnt run a hot wire out to the copper rod to measure current or anything???

Heres how the service entrance wiring including the Neutral and Equipment Ground Buss and the No 4 bare copper "Grounding Electrode Conductor" and the copper rod "Grounding Electrode" are all configured

1) At the incoming main service panel the Neutral Buss is bonded to the Equipment Ground Buss.

2) The Neutral/Ground is connected to a "Grounding Electrode Conductor" (No 4 bare copper wire) which leads outside where its bonded to a "Grounding Electrode"

3) A "Grounding Electrode" is usually a "Made Electrode" such as a copper rod or rods driven into the earth or perhaps other suitable "grounding electrodes" such as buried metal water pipes or structural foundation steel etc.

4) SOOOOOOO if you attach a hot wire out to that copper rod, theres 120 VAC across an almost dead short as 10 to 20 feet No 4 bare copper wire AINT MUCH RESISTANCE and the breaker will pop almost instantly

5) AND THATS TRUE REGARDLESS IF THE ROD IS DRIVEN IN THE EARTH OR JUST LAYING THERE OR UP A MONKEYS BEHIND LOL

Nowwwwwwwwwww if you didnt bond the Grounding Electrode copper rod to the service entrance Neutral (as is required at weatherhead riser or meter base or in panel) and you ran a hot wire outside and stuck it in the earth BUT NOTTTTTTTTT TO THE COPPER ROD then there would be measureable mother earth resistance between where you stuck the hot wire and over to the copper rod grounding electrode BUT IF YOU TOUCH THE HOT WIRE DIRECT TO THE ROD the resistance is lowwwwwwwwwww and the breaker will pop instantly as No 4 bare copper wire just aint much resistance between where it attaches to the rod and to the incoming service Neutral (panel or meter base or weatherhead riser)

Sooooo please explain how wiring off a 20 amp breaker and connecting it outside direct to the ground rod (assuming all is wired proper and per code) is a measure of the resistacne of what???

Of course if you run a hot wire out to earth NOT on the rod some current will flow and the resistance is that of the earth between your wire and over to the driven rod and that depends on distance,,,,,,,,,,moisture and mineral conrent of the earth,,,,,,,,,,how much the rod has contact with earth etc etc etc...BUT I JUST DONT UNDERSTAND HOW THATS ANY GROUND INTEGRITY TEST LIKE A MEGGER PERFORMS???????

PS In the event the rod is nottttttt connected to the Neutral (as NEC and alllll codes Ive ever seen require DUH) and you run a hot wire to the rod,,,,,,,then current will want to flow allllllll the way out to where the service transformers Neutral is bonded to Mother Earth and that may be 50 or more feet of earth and thats a bunch of resistance and low current flow but I dont see how that measures much of anything meaningful since it depends on how FAR FROM THE TRANSFORMER youre located.....ya gotta explain your and Buick mans method

Never too old to learn, please help us all out here LOVE SPARKY CHAT AND LEARNING (even at my advanced age lol) PLUS HELPING OTHERS

Ol John T

In my typically satuarated clay soils it's pretty easy to get a great ground from a single 6-8 foot rod. It's bottom half will be in water 95% of the time.

We've had some dry weather for 9 months now. This winter I had an odd deal - the sink in my house was 'ticking'. Think I wrote about it then on here?

Anyhow, took me 1/2 a day to figure out it was not a leak or drip I was hearing, but actually the electric fencer was 'echoing' in the bowl of the sink.

The fence shorted out onto the steel posts driven a foot or 2 into the dry ground. We had a light rain making th surface ground damp, but the subsoil was still powder dry.

The old windmill with the metal pipe up to the house is near where the short was, by the ditch.

When they rewired in 2008, they bonded the pipes and the electrical ground in the house.

The fencer is 400 feet away in the corn crib,grounded to a lightening rod ground.

Somehow with the very dry layer of subsoil, all this combined to have the ground of the fencer running through the house, I'm thinking the insulation of the powder dry subsoil, with the water pipe, and the few inches of wet soil on top. Was very interesting. Never had that before, and once it dried ot the top soil was gone. As well as once we got a tad more rain and the topsoil is a bit wetter now, doesn't matter.

I can always hear when the fencer is shorted out when I walk past the service feed transformer, a very light buzz from it if my fence is shorted out.

--->PAul

This should help. Jim
Ground rod test

Darn, a body would have to be an electrical engineer to understand all that lol I just dont see how running a hot wire to the ground rod would suffice (see my question above)

Thanks for the post Jim

John T

Good logical trouble shooting used there. 99.99% of "electricians" would have given up or been wrong.

Used to use megger made by Biddle co. for checking ground resistance. Hand cranked dynamo created I think DC current that went through galvanometer calibrated in ohms. Megger was hooked to known positive ground and wire being checked. Current through galvanometer, reading in ohms would tell you the resistance of ground existing. Megger would also shock the heck out of you if not careful. Seems like it could read up to 1000 megohms. What you are trying to do is make sure ground or grounding is very low resistance like 20 or 40 ohms to keep equipment and personel safe. Dave (all I know from 20 years ago)

If I were trying to do it that way. I would put a nice 120 watt incandecent bulb in series with the 120 lead to the rod. An amp meter should show 1 amp, and could be checked against the same bulb on the same wire to the power companies neutral.
Taken to an extreme, a high power rheostat capable of dealing with 30 amps could be used to go from nothing to 30 amps, providing full spectrum earth worm evacuation.
Jim

I'm confused on this test also. The only thing I can figure is you perform the test before you attach the No. 4 wire to the breaker box. If the breaker would trip from canceling out the power against the rod it should be good at the time but the moisture content would vary from time to time. Another problem I have is how to test the resistance on the hot lead. I accidentally tested power one time with my multimeter in the Ohm mode and fried the meter.

You are only testing the rod .It is not hooked up to the panel just a #12 run to it temp.