2 "ground rod" questions (Thumper aka cable fault locator)

I have a particular device that I would like to test, which is called
a "thumper". It was made by associated research (model 8613) and is
comprised of two under-desk-refrigerator-sized pieces, about 600 lbs
total weight.
For those who do not know, a thumper is a device that delivers pulses
of high voltage (up to 25 kV DC in my case) and huge currents, usually
above 1000 joules energy, to a buried high voltage cable where an
insulation fault needs to be located to find out where to dig to
splice it. The lineman walks along the cable path until he feels
"thumps" under his feet from electrical discharges in the faulty
There are warnings on my thumper that say in big letters that it must
be grounded to a ground rod. For obvious usual reasons. I do not want to
ground it to my house ground rod for safety reasons. So I went to Home
Depot and bought their 5/8" 10' "copper clad" ground rod.
What I would like is to achieve two goals with this:
First is to ground the thumper to test it.
The second is to use this rod later for lightning protection. My house
is on top of a modest hill and was already hit by lightning. See
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So later on I could save some $$ on needing to install a ground rod
for that.
So, my thinking is, the second ground rod would go in the ground close
to the first rod, maybe 2-4 feet or so distance. It would be close to
where other electricals are located and would be in the area that
would be convenient for connecting to some lighting rod to be
installed in the future.
Is that a sensible plan in light of wanting to use that second rod for
the thumper?
How to drive this ground rod. I have a decent compressor and a cheap
"medium" air hammer. Would I be able to drive it in my clay soil? I
read somewhere a suggestion to dig a small hole and fill it with
water, which would then liquefy the soil under air hammer's
pounding. Is that really helpful? How to actually angage an air hammer
to a ground rod?
Reply to
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On the first question: Your existng ground rod is already provides lightning protection to your electrical supply. If you are going to add a ground rod it should be the length of the ground rod or 10 feet in your case from the existing ground rod and they should be bonded together. If you are going to install a lightning protection system this quite another story. The NEC does not cover lightning protection systems but has this to say:
250.106 Lightning Protection Systems. The lightning protection system ground terminals shall be bonded to the building or structure grounding electrode system. FPN No. 1: See 250.60 for use of air terminals. For further information, see NFPA 780-2004, Standard for the Installation of Lightning Protection Systems, which contains detailed information on grounding, bonding, and spacing from lightning protection systems. FPN No. 2: Metal raceways, enclosures, frames, and other non-current-carrying metal parts of electric equipment installed on a building equipped with a lightning protection system may require bonding or spacing from the lightning protection conductors in accordance with NFPA 780-2004, Standard for the Installation of Lightning Protection Systems. Separation from lightning protection conductors is typically 1.8 m (6 ft) through air or 900 mm (3 ft) through dense materials such as concrete, brick, or wood.
On your second question about driving the ground rod. I have driven many without pouring the water. I have used a sledge hammer, a pipe driver, and an electric jack hammer equipped with a special hollow bit that goes over the top of the ground rod supplied by the local rental company.
About your thumper vibrating the earth - never heard of this before. The one's I used required a sensor attached to head phones.
Reply to
I am about to go to bed but just wanted to quickly comment that you don't use an air hammer. You push or hammer the rod in as far as you can, withdraw and pour water in the hole. You then push/pull the rod to gain more depth. You withdraw, pour in more water and continue with using the rod as an hydraulic piston until it is in all of the way.
Push, withdraw, pour in more water as hydraulic fluid and push; ad infinitum.
It is magic unless you hit a large rock.
Reply to
We drive ground rods all the time for portable generators 225KW and up. The easiest way is the ever handy Milwaukee hole hog. Spin that rod into the ground as deep as you can get it. Once it's set try and pour as much water as you can around the rod to saturate the soil. (about 1 1/2ft circle) Be careful and don't create a large wet area.
Reply to
Just try the hydraulic method. I have tried them all and the hydro is magic.
Reply to
Hey Iggy,
I would personally want the test ground rod an order of magnitude of its length away from the house, under ground utilities, neibouring buildings etc. I also reccomend you wear rubber boots while testing as under high voltage fault conditions significant potentials can be developed over a fairly short distance at the soil surface for some soil types and moisture levels. Unless the bulk resistivity of your soil is extremely low, you will get significant coupling between rods seperated by one rods length. Try 50 to 200 feet away from any structures. If you must drive the rod near the house, disconnect all electronic appliances in the house from all signal and power cables before you start testing. From the specs you have given, if you are too close to it, the thumper is easily capable of causing ground transients comparable to a nearby lightning strike.
Reply to
Ian Malcolm
Ian, thanks. You gave me some good reasons to pound the rod away from other rod. Also, I will control the thumper with something insulating, like a dry wooden board, and will use minimal voltages (like 5 kV instead of 25 kV). I may also stand on a plastic bucket just in case.
Reply to
Wood is not a reliable insulator at these voltages. Plastic is your friend.
Reply to
Steve Smith
The IEEE Green Book recommends one ground rod length. That is where I got it.
Reply to
Hi Iggy,
If you are really interested in lightning protection for your house you should look-up the "Motorola R56 manual" communications site grounding specification.
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will give you some info to start with.
Several equipment sites I used to work at were built to this spec. Lightning would still damage equipment there, but it was a whole lot less than not having it. You can't stop damage from a direct hit short of having everything disconnected. No power hooked up, no phone cables, no ground connections... just a box with no connections what-so-ever. IMO the telephone connections are a bigger problem or more likely point of entry rather than the power connection.
Keep in mind that willy-nilly adding ground connections could possibly make matters even worse than they already are. R56 is almost insane grounding procedures and damage still occurs...
Reply to
Leon Fisk
Well Iggy is planning on testing a device intended to generate extremely high current with enough voltage to overcome high resistance connections etc. If under fault conditions, the return path is via the soil to the test setup ground rod, it will couple into any long metallic objects such as utility cables either by induction or even direct conduction if they dont have excellent insulation. It would not be unreasonable to expect an induced current of tens or even hundreds of amps.
If Iggy has effictive lightning protection with multiple ground rods round his building perimiter each with a resistance to ground of less than a couple of ohms linked by a heavy bonding conductor and all incoming services are bonded at a single common point to it, with spark gaps and transorbs for all comms ccables, then all should be well, but if he has a single reletively short ground rod that may have had a resistance to ground of up to 25 ohms at the time of installation, well he's going to suffer the mother of all ground bounces.
Worst case, what do YOU reckon the chances of his PC and phones surviving a 10 to 20 KV high current transient between the mains supply and the phone lines are? I reckon we'd not see him online again till sometime near the end of next month at the soonest (assuming he's got cash to spare for a new PC, or a laptop on the shelf or whatever) and he might be offline for longer if he fries enough kit at the exchange to piss off the telco.
Mr Muller and a few others might think Christmas has come early :-) (not intending any slur on Nick), but I for one admire Iggy's persistance and willingness to expand his knowlege with *TOUGH* projects and would regret it if he dropped off the net.
Now if he just wanted the extra ground rod for lightning protection, I suspect your advice up thread is right on the money especially as you state its based on IEEE reccomendations. I'd have to research the relevent electrical code for Iggy's jurisdiction to confirm your advice and as I am *NOT* qualified to practice as a professional engineer in his jurisdiction, my approval would be of no real value.
Life's too short to tilt at EVERY windmill :-)
I dont think the IEEE anticipatied Iggy!
Reply to
Ian Malcolm
Interesting links. Thanks.
Reply to
Ian Malcolm
Ian, thanks for your friendly advice.
See another post (outcome post) that I posted today. I tested the unit more today. This thing seems to have a ground fault (manifested by blowing GFCI), and thus it should be considered broken. I will part it out and will try to learn something as I do so, it has a lot of interesting HV parts that I mentioned in the outcome post.
Reply to
I've seen some phantom GFCI tripping on the assymetric inrush current on larger high voltage transformers especially if one side of the secondary is grounded. I wouldn't write it off before it had failed a Hi-Pot test between the commoned live and neutral and chassis. Some stuff just cant be run off a consumer GFCI.
Before parting it out, it might be worth seeing if there is any interest in it from the Tesla coiler and coin shrinking communities.
If you do part it out make sure you have worked out a safe procedure to confirm the capacitors are fully discharged and keep their terminals shorted in storage. (I seem to remember this issue coming up with a previous purchase you made)
Reply to
Ian Malcolm
Well, I just tried running it on a regular outlet, it still does not work. Which may be because I am not doing it quite right, but I do not have a manual, and neither does Associated Research. I connected things the way that makes sense.
Well, you see, I am a little leery of selling a unit that may not be functioning right, to people who may not be very good at never making any mistakes.
Remember that the energy stored in this unit is roughly equal to kinetic energy of a high power rifle bullet (1500 joules, roughly like a bullet shot from a Kalashnikov).
I do not want some chump to die just because they were a little too stupid and did not quite figure everything that was wrong, even if legally I would not be at fault I still do not want it. It is not the same if it is sold by components. Many if not most of those coilers and such, are wannabes with not too much clue.
The parts there, are very fun parts and will likely arouse a lot of interest by themselves.
Yes, sure, I will do that -- though there are internal shorting devices built into this associated research -- but I will double check it safely and will wire it shorted for storage.
Reply to
If things go terribly wrong, he could become a candidate for next year's Darwin Awards...
Reply to
I don't know how you got a hold of one of these, but thay are LETHAL.
I would not even think of turning it on without someone around who knows how to use it...
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I have these hand planes I make and I need a better finish on the brass. I have sanded the sides to 400 and to 600 grit but if the side is not perfectly flat it's pretty much impossible to get even scratches. this is using any of three belt sanders. I was thinking of some kind of brushed finish but I am not sure what to use. it would be nice if it did not show fingerprints. the outside is what I am talking about the inside I forgot to do before I assembled the plane and I had to use a file.
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Reply to
Steve knight
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Unka' George [George McDuffee] ............................... On Theory: Delight at having understood a very abstract and obscure system leads most people to believe in the truth of what it demonstrates.
G. C. Lichtenberg (1742-99), German physicist, philosopher. Aphorisms "Notebook J," aph. 77 (written 1765-99; tr. by R. J. Hollingdale, 1990).
Reply to
F. George McDuffee
it is a cool method. but I don't have a lathe to do such work. I only have a mill and sanders for my metal work. I thought about buffing them out but I don't know if my sanding is good enough.
Reply to
Steve knight

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