how to get ground resistance <0.5ohm

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winwin

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Dear
Please help me find the right chemicals to reduce the ground resistance for grounding a cell phone site equipments.
Required resistance is less than 0.5ohm.
Regards
Nirpal

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Way to many variables to even begin to cover this topic here. In all seriousness try XIT and/or the other firms like this out (do a web search) they will tell you exactly how to try to achieve a low resistance ground, after some initial testing.
 
Well were not a expert but copper sulfate and a mix of rock salt will lower your resistance just digg a circle 2 feet around your ground rod or rods 2 feet deep pour add water . cover re test see if its lower .best to ya
 
Well as a telecom engineer who designs cell tower grounding systems I have never heard of such a requirement to get down to .5 ohms and see no point in it. As a ex Substation engineer we never went spec'd lower than 3 ohms in a massive 750 KV substation, although they usually were 1 ohm or less after being built.

Personally i don't think it is possible or at least feasible to get to .5 ohms. Sure the spec doesn't say 5 ohm's?

At any rate there are a number of ways to get the impedance down by using chemical ground rods like those made by XIT, in conjunction with using bentonite clay, radials, and ground mats.

I concur with Brian you should sub-contract the work to companies that specialize in grounding applications like XIT. But .5 ohm's good luck.

To be honest with you most of these specs are designed to do one thing and one thing only. Force the contractor to have a planned grounding protection system to serve a specific purpose like lightning protection and take discretion out of the EC hands by driving two rods in the ground and calling it a day.

I will give you a tip though. I don’t shoot for specific impedance. I use a cookie cutter design for all sites and it starts by using the towers concrete peers and rebar, then install an XIT rod at each leg of the tower, build a ring around the tower and equipment shelter, radial out from the tower and shelter to the fence line, and another XIT rod at the hatch entry port of the shelter on the ring line surrounding the shelter. Impedance is whatever it is, as long as the design I made is installed properly I could care less what the impedance is. I have a couple of other things I do, but that is a trade secret.
 
winwin said:
Dear
Please help me find the right chemicals to reduce the ground resistance for grounding a cell phone site equipments.
Required resistance is less than 0.5ohm.
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I've worked cathodic protection sites where a low ground resistance was speced - frozen ground, high resistivity. Their solution was 300 foot drilled wells filled with coke breeze and cast iron anodes - often more than one per site.

If they truly want low ground resistance, it isn't cheap.

The few chemical grounds I have seen only worked well for the first test.

cf
 
Well we do lots of grounding mostly power distribution and we install a common 3 rod delta system each rod 30 foot plus down cad welded each rod is tested and most pass a 5 ohm or less test by spec . A 3/0 copper is cad attached 30 foot apart on the rods per spec . the whole delta is always less than one ohm every time i guess its our ground in florida but we never use chemicals to get results and we only test the old 3 point fall of potential test per spec . IMO the clamp on testers are not actuate for a good test . Now we only do new construction work . best to yas
 
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IEEE Std 142 requires large commercial installations to be <5 Ohms and Generating or transmission stations to be <1 Ohm, it is common for the owner to require a lower spec knowing that the values may increase over time, specifically if chemical treatments are used, so 0.5 Ohms is not that odd for certian installations.

That being said, this is going to be a large, complex, expensive grid that should be designed and tested by specialists in this feild.
 
Well touch voltage look at voltage and personal in a yard or a high voltage area between points its not 277 volts or 120 volts it lots of potential , i would like myself to be at a higher resistance to ground point so when it crosses in the air point to point meaning flashing spark you have a higher resistance then the lower resistance point it may save your life and resistance changes over the years so lower is better when it fails to maintain its resistance . comments best to yas
 
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ohmhead said:
Well we do lots of grounding mostly power distribution and we install a common 3 rod delta system each rod 30 foot plus down cad welded each rod is tested and most pass a 5 ohm or less test by spec . A 3/0 copper is cad attached 30 foot apart on the rods per spec . the whole delta is always less than one ohm every time i guess its our ground in florida but we never use chemicals to get results and we only test the old 3 point fall of potential test per spec . IMO the clamp on testers are not actuate for a good test . Now we only do new construction work . best to yas
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What kind of TE are you using if not clamp-on? Have a web link?
 
Thanks for the responses

Thanks for the responses

we sincerely thank all members for helping us out :smile:
has any one tried Bentonite and Salt mixture, if yes, how long it works?
 
SmithBuilt said:
Just curious, what is the reason for getting the resistance that low?
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Thats' the problem I am having with the spec. I can understand for a high voltage sub-station, but not a cell tower site.

I design them for Verizon Wireles, ATT, and Alltel. None require nothing that low, nor have any need to. All cell tower sites are served with single phase 240/120 200 or 100 amp services. The main concern is lightning protection, but impdedance does not have a lot to do with that.
 
[QUOTE=76nemo;What kind of TE are you using if not clamp-on? Have a web link?

Well just a old time vibroground your standard galvanometer type synchronous vibrator with two test rods the company who manufactures these is associated research ,inc we also have a few new electronic types three and four points , most job spec engineers request a three point test only .we test 72 hours after a rain fall and test at high noon and again the following day all tests are witnessed by a electrical engineer and the electrical inspector on site we must get 5 ohms or less . Iam sorry dont have a link to any testers but there pretty much standard everday stuff nothing special .take care
 
has any one tried Bentonite and Salt mixture, if yes, how long it works?
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One. It passed the initial test. We tested again that winter (frozen ground) and it failed. The next spring, after the ground thawed, it still failed. I added a 5lb bag of rock salt and 5 gallons of water. Amazingly, the next week, it passed.

I don't know how it fared after that.

cf
 
winwin said:
has any one tried Bentonite and Salt mixture, if yes, how long it works?
Click to expand...
Used lots of Bentonite and chemical salts, not sodium chloride as it violates EPA rules.

All chemical rods use both. You core a hole to set the chemical rod in and backfill with bentonite clay slurry. Then the rod is filled with a secret chemical. Well it is no secret it is either Magesium Sulfate (Good ole Epsom Salt) or Copper Sulfate. Rock salt works great, but as I mentioned is illegal to use.

Another good way to use bentonite is with radials. You dig out a trench to lay the radial in fill the bottom with bentonite, lat the radial in, then cover with more bentonite, then use th eremoved soil to finnish filling the trench.

Or you can use bentonite with regualar ground rods. Instead of driving them into th eground you core a hole like you would a chemical rod, except you use a standard ground rod and backfill with bentonite. Its pretty easy to do you just make a slurry in a bucket, wheel barrel or cement mixer and pour it in.

There are lots of chemical rod makes out there just GOOGLE "CHEMICAL GROUND RODS". Some of th ebettr ones are XIT and ENRICO but there are a ton of them and it all uses the exact same principle and chemical.

FWIW Bentonite is also known as drillers mud and dirt cheap, and your wife powders here face with it. :cool:
 
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HVDC power transmission systems use ground as a return path, and thus the electrode system has to have a low impedance whilst passing currents of 1000 amps or more continuously. These guys have done a lot of work on consistently achieving low ground impedeances. Though being DC I suppose it should be resistance.

Most of the infomration on this is published in journals with articles not freely available online, but quick google brought up a short publicly viewable PDF: Performance of HVDC Ground Electrodes in various Soil Structures.
 
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