Recently moving into an old house one of my main concerns was the
One question I have is there a required size of cable for a 100 amp
When we first moved in I was looking at the service panel. I did not
see a grounding cable to the outside. Which I know meant no grounding
rod. What scared me the most is the grounding wire that was run went
to the gas line. That for now was changed to the water line.
I would like to install the grounding rod myself but would like to
know if it matters as to what size grounding cable to run for a 100
I assume you mean a rod for each phase? Why? And what
good would a "ground meger" be? I assume again the you
Just curious; I have NEVER seen more than one rod used
for any entrance on any house.
So I can't spell!! You are correct that only one is required but it must
have a specific ground resistance, which you need the megger to test. If you
don't have one, you must install a second rod six feet apart
Why? I have a 200 amp service and a single rod.
The critical factor, at least here, is the length
of the rod and depth the rod is driven down.
And, what the hell is a ground meger? Did he mean
a ground meter? If so, what is a ground meter?
Did he mean measure the ground with an Ohm meter?
And the response is equally crazy. "A rod on
each phase" means the questioner doesn't know
anything about electricity or the correct terms.
And he things meger might be megger, but what the
heck is megger?
Let me splain it: NEC rules change constantly. There was a time when, if you
had a metal water pipe, it was sufficient for grounding. Next it was
required to back the water pipe up with a ground rod. If you had a well with
pvc you needed two ground rods. The latest change is that you must determine
how well connected to the earth your ground rod is, which is done using an
expensive measuring device called a megger. If you don't have one many
jurisdictions require you to add an additional rod. IMHO it makes sense. If
you drove an eight foot ground rod into dry sand it probably isn't going to
have any connection electrically with earth
I think the name actually dates back to WWII or maybe
even earlier. A "Megger" measures Meghohms, and thus
the name for its use as in "megging a line". I used
them a lot in the service to look for insulation
breakdowns in aircraft wiring. You apply the megger,
which was basically a high voltage generator, crank it
up, and measure the voltage at which current flows, and
then the current, and the readout would in meghohms.
It was a tiny scale, very hard to read, and you usually
got to use it in the mid day tropical sun, inside a
hell hole somwhere in one of the aircraft fuselage.
Just for grins, I jumped onto Google and the first
place I tried turned up one very similar to the ones we
Megger is the actual name of the instrument: try a
search on Google and you'll find lots of hits for
They've taken a much more modern design and
application of course, but the concept of all of them
seems to be the same: measuring current flow at
specified voltages and reading out the reults, in
resistance or impedance, whichever the case may be.
It was a surprise to me to see a megger used for ground
rod testing, but I did see a couple of links for that
purpose too, though I didn't open them. I would have
thought it more of a high current test, but apparently
not, which I can sort of see, because the two opposing
phases coming into a building each add or subtract for
total current, depending on the phase, but I can't
argue with facts, eh?
Earth grounds are "interesting' to say the least.
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On Fri, 22 Jul 2005 18:35:12 -0400, "Pop"
I'd hate to think of terror measures
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