Ian Malcolm writes:
JerryN wrote:
"Ignoramus22371" wrote in
message ...

On Sat, 16 Dec 2006 02:15:56 +0000, Ian Malcolm
wrote:

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.


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.


i
The IEEE Green Book recommends one ground rod length. That is where
I got it.

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 **** 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!


--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=-
& [dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.

If things go terribly wrong, he could become a candidate for next year's Darwin Awards...