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Thread: Earthing improvement products and ideas

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    Earthing improvement products and ideas

    Hi All
    I'm doing a new home installation and struggling to get a good earth.
    There is a drought in Cape Town right now and it's not helping
    The plot seems to have solid rock everywhere soon as I go more than 1m deep.
    I have installed a copper earth mat below the foundation, used lots of bare copper in the Trench to my wc1 box and knocked in two pathetically short earth spikes about 1metre deep.
    Resistance is still way out of specification.
    Auzzie sparks reckon I should use a jack Hammer to knock down the spikes but I doubt I will penetrate the rock so I am looking at possibly having holes drilled about 6metres x 3 for earth spikes and then filling up with bentonite clay.
    However, I'm not sure it's available in South Africa and I'm also not entirely sure who I contact for the drilling. Core drillers?
    I have spent most of my time working in industrial panel wiring and earthing is not something I have vast experience in, but I guess it's when you have issues like this that you really become *experienced*

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    Diamond Member AndyD's Avatar
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    Yeah, earth impedance in some areas of Cape Town can be a problem. What impedance readings have you achieved so far with your short earth rods, earth mat and the trench? What's your target earth impedance? What's you financial budget?

    On the tricky installations I usually connect to any structural steel in the building or even reference meshes in the slabs with a welded stud, just make sure you clearly mark any connections as being electrical earth. You'd be surprised how effective slabs and structural Ufer earths can be.

    The problem with multiple short rods, especially on a domestic plot, is that you get overlapping areas of influence which makes it less effective than a single deep rod, eventually you just run out of space. Also with a deep rod you're more likely to reach the water-table which is a good thing so rather than going with 3x 6 meter rods I'd suggest a single 18 meter rod will give you far better results.

    To answer some of your other questions, yes you do get Bentonite/Marconite locally, it's mined in SA. You could try an SDSMax jackhammer with an earth rod driving attachment but as you say, depending on the types of rocks you might not get anywhere. Drilling a hole is an option, it's expensive and a last resort, I'd suggest contacting one of the borehole companies.

    Bentonite

    Bosch HS1924 SDS Max Earth Rod Driver **Sorry about the price, maybe shop around and also try Hilti and Milwaukee dealers for their version. Atlas Copco do a hydraulic ground rod driver but I can't comment on it because I've never used one.
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    Dave A (20-Feb-17)

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    Thanks very much , I appreciate the advice. I never knew one deeper rod would be better, would probably cost me less to have one hole drilled. Waiting on quotes for drilling.

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    And thanks for link, we are blessed to have you guys helping out on this forum

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    Diamond Member AndyD's Avatar
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    You're welcome and good luck.

    You didn't say what impedance you've achieved so far with your short earth rods, earth mat and the trench?? And what your target impedance is....

    **Edit** If you're not financially afraid to drill it might be worth exploring a sleeved borehole which could be used as a borehole for water as well as the sleeve being used as an earth rod. Just a thought.
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    My last reply didn't make it for some reason
    I'm reading about 160ohms.
    Target is 20 or below.
    I did manage to get a1.8metre rod in between gaps.
    The borehole idea Is a great one. I have been quoted 5k to drill one hole do far but still need to shop around a bit.

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    Diamond Member AndyD's Avatar
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    Wow, so you've only got it down to 160 ohms with multiple short rods, earth mat below the foundation and bare copper in trenches etc. That's very little reward for lots of work, I'd be clinically depressed at this point if it were me so hats off to you.

    R5K for an 18 meter borehole sounds very reasonable to me especially if it's sleeved. Last time I had to drill for an earth I paid about double that price for a 25 meter hole and that was maybe 7 or 8 years ago so factoring in inflation the price you've got sounds very good to me. When we drilled we hit water at just over 20 meters so we went 5 meters more to accommodate seasonal water-table variations and called it quits. We didn't sleeve but with bentonite and a 5/8ths rod in the hole it gave us about 1.2 ohms Ra reading. It was sub-ohm when we included other parallel paths from existing rods and foundation steelwork etc.

    What is the supply? ie single phase or 3-phase, how many Amps etc? How did you arrive at a 20 ohm or less impedance requirement? Also what earthing arrangement is the supply ie TNCS (PME), TT, TNS ?
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    what area is it? i found out where ysterplaat got its name from. go down a metre and you hit rock. i also found one long rod is much better than multiple short rods. when you lay the supply cable to the boundary lay 10mm bare copper in the trench. sometimes helps.
    if you can jackhammer through the plaat then 2 x 2,4m spikes on top of each other should do the trick.

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    Thanks and my apologies, made a typo, earth electrode resistance needs to be 2ohms or below , not 20ohms and is TN-C-S.
    Arrived with that value with formula ohm max = 230/(60x2) = about 2ohms.
    As its a 230vac 60amp installation.
    I managed to get a much longer spike down and need to retest, however the plot thickens... my Meter may not be working properly x) MT330, have had ongoing issues and just been calibrated.
    I'm going to borrow a friend's Meter and retest.
    Andy the only reason I'm not pulling out my hair is that I recently raised my prices so feel quite happy with the profit margin on this job.... but that extra profit is probably now gone lol

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    I was quoted 5k subject to site inspection for a 6m hole at diameter of round 40mm, no sleeve or anything so might cost more than that for a deeper hole especially when they see the rock

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