"Jim Miller" wrote in message
oups.com...
Got to the library today and read 250, 800, 810 and 820. Interesting
section in 810 that effectively requires all Ham antennas to be 14AWG
or greater. Makes products like Wireman's 18AWG copperclad steel a
nonconforming wire for antennas.

I was planning to use the 18AWG for my 88ft center supported doublet.
The unsupported length would be about 50ft. The NEC is pretty coarse
grained at "anything less than 45meters".

Did I misread this? Makes "stealthy" antennas pretty difficult.

Jim, the NEC, in states that have adopted it, does not regulate low voltage
systems or antennas or comonents thereof, beyond (varying interpretations)
of the first bonded ground system. NFPA-780 Standard for the installation of
lightning protection systems DOES apply best practices beyond that point,
and yet it is not actually code. But it is referenced and for all practical
purposes, becomes code where referenced in NEC. Confused? ;-)

Your antenna may or may not be considered "low voltage" - this rarely if
ever comes up in construction permitting btw, but this group could debate it
for days. Your antenna system definitely becomes high voltage when afected
by a nearby or direct lightning strike. In my unqualified opinion, the two
reasons for minimum recommended wire gage, are withstand of high energy from
faults or lightning (fire and electrical shock hazard there), and durability
of external systems, the failure of which compromise parts or the whole of
electrical and lightning safety.

Most of the antenna language you collected are suggestions that are
interpreted as best practice. But they are not regulated and it probably
should omit comments such as you took somewhat out of context in your
example. Where NEC can be applied strictly (or not, again depending on your
state) is where antenna feedlines traverse inside spaces of dwelling,
commercial or industrial structures, and antennas attached to roof systems,
wall systems, interfaced with ground systems, etc. In those circumstances,
the possibility of death, serious injury, and severe property damage is a
real possibility where improper methods of construction would be allowed.
Minimum air-spacing in walls/attics is one example of that requirement.


Section 250 is pretty opaque on grounding and bonding. I came away with
the impression that they wanted ground rods (8ft) every six feet. Did I
misread this as well?

tnx
jtm


I think you did, yes. The relevant part of art.250 to comprehend, is the use
of bonding in both electrical safety and lightning protection. In electrical
safety, the purpose of bonding = fault clearing by low impedance path to the
circuit breaker, NEVER by providing a circuit path to earth and
earth-to-circuit breaker as the path to clear the fault. This is where 99%
of hams go astray, mostly because the daunted organizations of their
societies say grounding an amp, etc (to earth) will save their life. Wrong!
One radio engineer here, who I think is quite brilliant in those areas,
thought a ground-to-earth protected people, when in fact it could kill. This
is no doubt due to massive misinformation in the amateur world about basics
of electrical safety, as there is also about lightning protection.

Back to your ground rods - you should never modify or provide any electrical
grounding system for your high voltage AC system in a residence. Licensed
electricians are required for that. Your work will be related to grounding
and bonding an antenna system (including feedlines) to the mains electrical
grounding system, and that should be inspected but rarely is.

Your ground rods should be at least their sum's depth apart, and should be
sunk a minimum of 10' in the ground (or 3' deep if laid horizontally), or
the required number of feet in a UFER ground (bonded reinforcing rod in
poured concrete). 16' ("conductor" sum's depth of two 8' ground rods sunk
10' deep) is generally considered the separation standard you questioned. It
is described in great detail in NFPA-780.

I really applaud your actual work in the library on a subject too boring for
most radio enthusiasts to spend much time on, even though their very lives
(and others around them) could depend on it.

73,
Jack Painter
Virginia Beach, Virginia