cool trick, and at the price of an electrician per. hour, you’d make enough on that one job to go buy the test equipment to do the same thing in 1/5 the time, make less money, sell your equipment and do it this way again. seriously, good info.
For example a house with a plastic water service and a single concrete encased electrode would be NEC compliant.
There is no way to properly measure the resistance to earth with a standard meter.
Yes you will get a reading on the meter but is meaningless.
The reason that expensive ground resistance testers actually sell is the fact it can not be done without them.
The three point fall of potential test is probably the most accurate method available but is not cheap.
The meter is connected to the grounding electrode being tested and two temporary probes put into the ground as far as practical from each other. Then the meter makes the test and gives you the resistance of the electrode under test to the earth.
You are correct the NEC is not the issue here. The issue is do you have a good ground. To measure a ground system one must have a complete ckt be it with test probes, water main, ground rods or re bar in concrete slab
The “cheap and dirty” test is giving you the resistance of your ground system. If you look at the clamp on ground testers they are doing the same thing. Resistance of the loop with an known induced AC current. The three and four point tests use test probes. Still measuring the resistance between two or more points. It all works and the numbers come out the same
Current is current with all meters – Yes the amount of current can change the amount of resistance (heating of material - chemical reaction)
NEC is not even addressing the impedance of the grounding system which is an issue in some systems.
Yes the cheap and dirty test is labor intensive but so is a 3-4 point. The clamp on ground test with a little AC is the neat way to go but one has to be in the business to justify cost of the test equipment
By the way where would an error be injected into the readings that would make them meaningless? I don’t understand. This is how many ground systems were checked before the fancy test equipment. Main problem was labor and ALL power must be killed to the system.
Help us out here. If there is something that I have been trained on that is wrong turn the light on for me. I don’t want to pass out miss information.
Well it is my brothers and I have seen it work…technically…lol…But have YET to see my brother convince a local AHJ it works…they had a local meeting and have started their own RULE…2 rods minimum…no exceptions testing or not testing…
So…we end up saying…well…no need to fight the MAN…just go with the normal plan…let my large Hammer Drill…drive them $ 10.00 rods down…lol
I think William Decker once said to me " on the boards" it must be hard to walk a fine line between being an HI and being an Electrician…well to be honest with you I don’t have a problem with it but again 18 years later it is very easy to say that…
As for HI’s doing this test, I would tell HI’s personally to stay away from it, if the local AHJ approved the installation on THIS crutial part of the inspection I would not worry about it…from not only a legal stand point but from a time standpoint.
I am not the fastest HI in the world…I know all the other areas of home inspections quite well ( except Boilers…lol ) but only really get into comments here on Electrical issues because thats really why I came here…to bring my REAL LIFE electrical experiences and to spit a little CODE at ya when I get a chance…
While I will agree…it may have some merit to test this I personally do not think the HI should go into that area. I think however on a report if you can’t view the grounding system which happens in MANY cases in older dwellings I am known to suggest they add a supplimental grounding electrode to a system that may only have a waterpipe ground…
In the end…actually doing the tests and giving feedback on it to the buyer could open a can of worms the HI might now want to fish with…now with that said…WHO am I do discourage it…hell maybe even sell it as part of an enhanced electrical inspection…I don’t know…but the normal HI probably is better off checking the system fully, making comments on WHAT is missing or what they can’t see and reporting as such and in all cases of unawareness…defer to an Electrical Contractor…
Dang man…us electricians can’t let you guys take ALL the business…
I under standing about burning the bridge with the local electrical contractor but on older homes we would generating work for them
Would you offer to do it if ask or would you say call an electrical contractor?
I don’t think it is beyond the knowlege base of an HI if he or she wants to learn how to do it and also how to present the findings. Just like mold - moisture etc.
You got me going by showing me the price on the meter. I have more than that in my Fluke DVOM!!!
Strange enough…I did not see the device we are speaking of on your site…while I bring KUDO’s to your sales…unless you offer the exact item posted I can’t link to it…
Find out why the National Electrical Code “25 ohms or less” rule may have less to do with power quality than you think.
Nearly all electricians and electrical inspectors are familiar with the National Electrical Code requirement in Sec. 250-54, which requires the resistance to ground of a single-made electrode (e.g., ground rod) to be 25 ohms or less. Unfortunately, it seems many electrical professionals don’t actually test the grounding electrode system (GES) to ensure they’re meeting this requirement. Even fewer of you feel testing the earth ground system is worthwhile. From a power quality perspective, you may be right.
A GES provides:
• A zero-volt reference for the supplied or derived power systems.
• A path to dissipate lightning or fault current (for higher voltage systems).
• A path for the dissipation of electrostatic currents.
A GES consists of two components: the grounding electrode conductor (GEC) and the grounding electrode.
You can choose a bare or insulated GEC (sized per Table 250-66) in copper or aluminum. The GEC connects the grounding electrode to the grounded circuit conductor, the equipment-grounding conductor, or both, at the main service equipment or the source of a separately derived system.
The most common types of grounding electrodes (identified by Sec. 250-50 and 250-52) are:
• Structural steel
• Metal underground water pipe
• Ground ring
• Ground rods How to test. You should measure the resistance of an electrode with respect to the surrounding soil in the area. You can only do this by using the fall-of-potential method with a three-terminal, earth ground resistance tester. To properly test the resistance of a GES, you must follow some simple rules:
Disconnect the electrode under test from the rest of the electrical system. Considering this, it is not possible to test the grounding electrode system in nearly all circumstances.
2. Don’t use a meter that injects DC current into the ground rod. Do not use standard VOMs.
3. Don’t perform test measurements if the current on a GES is greater than 5A.
Contrary to popular belief, clamp-on earth ground resistance testers can be inaccurate in field applications. These testers require a low-resistance feedback loop with adequate spacing between electrode systems to provide meaningful readings. Many people often add a high resistance (caused by loose connections in the feedback loop) to the displayed value of the meter. Also, inadequate spacing between electrodes results in the meter only making a comparative bonding test, which almost always results in a low-resistance value. Why do I need to reach 25 ohms? The most credible answer to this question is: 25 ohms is a reasonable value to strive for, given the average soil resistivity for most regions of the United States. Keep in mind, however, that 25 ohms is not a requirement when you install multiple electrodes. This is only a requirement for single-made electrodes, per Sec. 250-56. If you drive the first rod and get a resistance reading greater than 25 ohms, the NEC allows you to drive an additional rod 6 ft away from the first rod.
Let’s say, for example, you drive a ground rod into the soil, but instead of testing that rod to see if it meets the 25-ohm criteria you drive the second. Once the two rods bond together, consider the GES complete. But if you don’t take a measurement, how do you know your installation meets Code? Reality check. In most commercial and industrial low-voltage power systems, technicians do not perform earth ground resistance testing. But this shouldn’t surprise you. An informal poll of 50 electricians found only four performed earth ground testing in the past. The reasons cited for not testing were:
• The testers were too expensive.
• The test was too confusing and took too much time.
• Two rods are good enough (most common response). Impact of power quality. Believe it or not, nearly all electronic equipment will operate properly without the benefit of a low-resistance GES. Power quality site surveys have shown that in situations where the grounding electrode resistance is between 5 ohms and 105 ohms, it doesn’t affect equipment. However, you can trace most problems to poor quality connections on the equipment-grounding system. Therefore, you should pay less attention to the GES measurement and more to the impedance of the equipment-grounding system and the verification of low-resistance bonding connections between grounding planes.
What’s the lesson here? Spend less time on the testing and qualification of the GES resistance and more time checking the bonding between locations and the equipment-grounding conductor impedance.
Being an EDUCATOR…I am FREE to post it…so some little girls in the office got scared from some “has been” and removed a good post for you guys to learn from…because they feared copyright…FYI…EC & M does not own the article…GEESHHHHHS
You should measure the resistance of an electrode with respect to the surrounding soil in the area. You can only do this by using the fall-of-potential method with a three-terminal, earth ground resistance tester. To properly test the resistance of a GES, you must follow some simple rules:
Disconnect the electrode under test from the rest of the electrical system. Considering this, it is not possible to test the grounding electrode system in nearly all circumstances.
Don’t use a meter that injects DC current into the ground rod. Do not use standard VOMs.
Don’t perform test measurements if the current on a GES is greater than 5A.
Contrary to popular belief, clamp-on earth ground resistance testers can be inaccurate in field applications. These testers require a low-resistance feedback loop with adequate spacing between electrode systems to provide meaningful readings. Many people often add a high resistance (caused by loose connections in the feedback loop) to the displayed value of the meter. Also, inadequate spacing between electrodes results in the meter only making a comparative bonding test, which almost always results in a low-resistance value.
Trust me I do understand the difference of a Point to Point DC resistance check and a AC three or 4 point check – Been there and done that but if you have a lost of time to check out your own home DC works. (Untill some one can show me otherwise)
Yes, I understand about noise and other currents. What I like is this thread that Gerry started has caused some of us to go back to the books to understand grounding and ground testing
