( ... )
Modern American electrical code requires a
big-sized bare conductor (and some minimum
length requirement that I forget) coiled into any
poured concrete foundation. This is an effective
ground.
Simply drilling into concrete and installing some
conductive rod is ineffective.
Some practitioners use multiple ground rods,
all connected together, driven into the earth, with
a big conductor from the ground rod array to the
service entrance. There are different sizes of
grounding rod, from 1/2 inch to 1 inc diameter.
Most of us have no control over the electrical
wiring we use.
With rare exceptions, initial electrical wiring is
proper. Problems show up after non-electricians
(handy personages, cheap M. Mouse laborers...)
show up to extend or repair things. It's hard to
wire things badly because the suppliers sell only
devices that conform to the National Electrical
Code--wiring things up is a matter of using the
right tinker toy, hard to get wrong other than
swapping the neutral and the hot (hot is either
red or black and connects to a brass colored
screw; neutral is white and connects to a silver
colored screw; ground wires are either green
or bare copper and connect to a green colored
screw).
If you own your own home and it uses a
grounding rod, consider sinking another one or
two or five or 27 and connecting them all together.
Multiple grounding rods reduce the impedance
of the barrier between a single grounding rod and
the actual dirt into which it's sunk by a factor of
the number of grounding rods (two rods halve
the impedance between the service ground lug
and true earth).
Note that the size of the conductor should be
huge (#4 at minimum, 0 or 00 or greater can't
hurt and might be correct depending on expected
ampacity). This conductor must connect each of
the ground rods to the others as well as (a single
length) to the service entrance bonding lug.
Note also that the devices that clamp the wire
to the grounding rods must be the correct size
and material for both the rod and for the wire.
If you have grounding problems, it's likely that
the original grounding components have
corroded or become loose. Either presents a
potentially dangerous shock hazard. (Adding
grounding rods to a working system does not
as long as you do not break the existing
connections.)
On 02/08/2015 12:52 PM, Gene Heskett wrote:
On Sunday, February 08, 2015 03:23:44 PM Ralf Mardorf wrote:
On Sun, 08 Feb 2015 21:14:12 +0100, Hermann Meyer wrote:
Old buildings didn't use grounds, they just have 2 cords and use the
second as ground and backline. In German this is called Nullung.
Potential issues are clear with this technique.
Actually I'm living in an "Altbau" with retrofitted concrete-footing
ground electrode. Potential issues could be caused by tons or grotesque
reasons. Reality has absolutely nothing to do with school books.
A ground into concrete is not much of a ground at all. On this side of the
small pomd, we are required to drill thru the concrete if its in the way,
amd sink 2, 8' copper rods directly into the dirt below the concrete, spaced
not less than 8 feet apart. And they are mandated to be connected to both
the neutral and the static grounds AT THE ENTRANCE SERVICE AND NO WHERE
ELSE.
I redid, most of it myself, the service here bsck in 2006, replacing a 60
amp entrace with a 200 amp entrace that the houses 60 amp is now a
subcircuit, fixing several problems that I'd be willing to bet were never
inspected when this place was built in '70. I had lost several bits of
computer hardware, modems in particular due to the EMP from nearby lightning
strikes. I have witnessed the transformer pole across the street that my
service comes from, being hit several times, with no damage to anything in
the house since.
The way I have this room wired today, a lightning strike can make the
service and everything in here bounce 50 to 100 thousand volts, enough to
give me a doorknob shock from a wired keyboard. Zero failures in this room
since 2006 when I did that. That didn't even hurt that keyboard but now I
use wireless with several inches of air gap. And keep batteries on hand.
;-)
Cheers, Gene Heskett
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