Backfill around an earth electrode?
Backfill around an earth electrode?
(OP)
Hello all!
When you install an earthing electrode for a LV M.E.N distribution system, what sort of backfill should you use around it? Does it depend on the soil makeup to the area?
I am told to use bentonite and i dont know what it is and cannot find much about it. Is there a better material?
Also, how much backfill? For the electrode to be installed, you only require to bore a 50mm diameter hole for it to fit down. Should you excavate a larger hole and have more backfill around the electrode?
Thankyou
When you install an earthing electrode for a LV M.E.N distribution system, what sort of backfill should you use around it? Does it depend on the soil makeup to the area?
I am told to use bentonite and i dont know what it is and cannot find much about it. Is there a better material?
Also, how much backfill? For the electrode to be installed, you only require to bore a 50mm diameter hole for it to fit down. Should you excavate a larger hole and have more backfill around the electrode?
Thankyou






RE: Backfill around an earth electrode?
Larger diameter electrodes such as chemical filled varieties must be installed in a bored hole. These should be backfilled with a material which has good conductivity and will remain in good contact with the surrounding earth. Bentonite is one such material. Bentonite is a type of clay formed from weathering of volcanic rock.
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Some grounding product suppliers have their own variations of bentonite which they sell under different names.
http://www.lyncole.com/p.lynconite.asp
RE: Backfill around an earth electrode?
What you really need to do is to couple 2 ground rods with ground rod couplings and drive at least 16 feet into the ground it the soil will allow it. Alternatively you can drive your rods at a slant so that most of the rod is in undisturbed soil.
According to another source ( I forget where but it may be the IEEE Green boook ) bentonite clay actually increases ground resistance by squeezing out water.
RE: Backfill around an earth electrode?
Driving rods at a slant is an option where rock or other obstructions are encountered. Typically the objective is to get the maximum depth to maximize contact with permanently moist soil.
I've never heard your concern regarding bentonite before. I would be interested to know the source.
RE: Backfill around an earth electrode?
You need to determine how low a resistance ground you need and what the resistivity of the soil is to design the grounding electrode.
If you need a lower resistance, driving a longer rod would generally be better than using a bored hole with low resistivity material like bentonite. Bentonite or a proprietary low resistivity material (Eritech offers GEM http://www.erico.com/products/GEM.asp) effectively increases the diameter of a rod in high resistivity soil. To do this you need a larger diameter bore, at least 150 mm. You get a greater decrease in ground resistance by using a longer rod than by using a larger diameter, but you can do both if you need low resistance.
Bentonite, also known as drilling mud, needs to be kept moist to be effective, so it has to be in soil with good moisture.
The worst thing you could do is bore a hole only slightly larger than the ground rod. This won't allow complete compact backfill and will not give you a large diameter of low resistivity material such as bentonite.
RE: Backfill around an earth electrode?
There is also someone here at engineering tips who is with a Colorado electric utility who says that the portions of their system that have 17 foot ground rods ( using rod couplings ) have ZERO lightning damage.
If you know anything about basement waterproofing you know that typically in most of the U.S. the basement acts as a gigantic dug water well. Typically, the soil underneath a basement floor is saturated with water unless you live in a desert or there is a severe drought. A slab on grade building is a totally different story.
Reinforcing steel that is at the bottom of a foundation is now a mandantory grounding electrode in the U.S. if available.
According to the IEEE Green book backfilling a ground rod hole with concrete also works.
There is also a radio amateur in the American southwest desrt who has had considerable success with a mixture of gravel, gypsum, rock salt, and a SMALL amount of bentonite clay. The small amount of bentonite clay provides MODEST compaction and still allows a perforated pipe to be used to add salt water.
Bentonite clay is a valid idea just as long as you do not use 100%
RE: Backfill around an earth electrode?
Bentonite may works and could be effective in rare occasions. This material has several disadvantages in dry environment and cost and installation time may be significant high. Beware that there are other methods more effectives for reducing ground resistances such as adding rods, increasing rod lengths, chemical rod, Ufer ground using the concrete foundation, etc or a combination of these methods.
See the enclose info for additional details in this matter. http://cuky2000.250free.com/GND_Electrode1.JPG