Once again the wisdom of 150 years of Telephone Craft can be used as
a good source of knowledge:
Grounding conductors are subject during lightning strikes to a pulse of
voltage
that travels along the outermost molecule of copper in a conductor. Sharp
bends in
grounding conductors are avoided because the pulse may very well jump
from
the radius of a sharp bend.
Surrounding grounding conductors with 360 degrees of metal as found in
box
connectors or separately-grounded conduit, etc., is a practice called
"girdling."
This is severely frowned upon because the pulse in a lightning strike may
cause
heating severe enough to melt the grounding conductor at the girdle
point.
Grounding conductors subject to lightning strikes physically move and
change shape
all within a few microseconds. This movement is enough to dislodge unfirm
electrical connections. Additionally, this effect magnifies the
copper-to-copper
connection's contaminant layer where one molecule of oxidation between
copper conductors will heat up and possibly blow apart.
For this reason grounding conductors are not twisted and wire-nutted, nor
are they
bug-nutted with mechanical compression devices. The most secure grounding
connection is made with a compression lug where the conductor is
burnished
with scotch-guard, coated with No-Ox-Id and connected with suitable
hardware
to a mating surface also prepared.
Soldering is avoided specifically because the conductivity of the solder
amalgam
is different than copper. This is where the heating during a lightning
strike can
instantly vaporize the solder joint and blow the conductor apart.
Exothermic
welding is preferred on certain joints where eventual corrosion may
render a
mechanical joint ineffective.
The best advice for home owners is to use two bugnuts on top of wire
splices that
have been cleaned to a bright metallic finish and coated with No-Ox-Id,
and then
covered with vinyl electrical tape. Connections to grounding rods should
be
Cad-Welded (exothermic), but that is a dangerous procedure and if one
doesn't
have suitable training should be avoided: The catalyst uses a mixture
that is
highly flammable and explosive. Ground rods should be burnished and the
ground wire clamp should be also, and No-Ox-Id should cover the joint
with
a liberal covering of vinyl tape over the joint with the entire joint
buried
18 to 24 inches below the finished grade.
If anyone has specific questions on approved telephone craft they are
welcome
to contact me on or off-line at any time.
Work Safely.
Hal Mandel
W4HBM
On Thu, 20 Oct 2005 10:55:28 -0400 Tony King - W4ZT <amps080605@w4zt.com>
writes:
>
> R.Measures wrote:
> > On Oct 20, 2005, at 6:52 AM, Tony King wrote:
> >
> >
> >>I wonder if we could clarify this question?
> >>
> >>Solder in protection grounding circuits is a no no because the
> thermal
> >>heating of a lightning strike will likely cause the joint to open
> and
> >>that's why the recommendation for exothermic welds (especially to
>
> >>ground rods) but soldering was always approved for current
> carrying
> >>circuits since it makes for a superior electrical connection. I
> >>subscribe to the twisting, soldering and then applying the wire
> nut
> >>method with the addition of a few turns of Scotch 33 to keep that
> nut
> >>from turning. Solder is always better than a simple twisted wire
> >>connection so that is why I wondered if it really is a violation
> (not
> >>allowed) or just "not required". Is there a specific code section
> that
> >>prohibits soldering in current carrying wires?
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