On 7/31/2011 16:32, KD2AIP wrote:
Anyone have experience making a dipole from 18 gauge speaker wire? I
have a whole lot of it lying around the house, and was wondering if I
could put it to some good use.

Be aware that the National Electric Code (NEC); that is enforced as law
in many jurisdictions; forbids the use of wire that small for aerials of
radio stations. The NEC specifically requires that size fourteen
American Wire Gauge be the minimum size that is used.

In point of fact you are unlikely to ever get inspected unless some
neighbor is raising a stink about your antenna. The danger is that in
the event of a physical failure of the antenna that brings harm to
anyone or anything, the use of non code compliant size wire will shift
all blame on to you. That could include a trespassing neighbor kid
yanking on your coax lead in and being burned before you realized that
the antenna was in direct contact with him because the wire of the
antenna that was supporting the coax had failed. The reason that you
might be blamed for something that at first blush appears to be
outrageous conduct on the kids part is based on the idea that anything
like that which is not sufficiently guarded so as to prevent that kind
of occurrence is considered to be an attractive nuisance in the eyes of
the law.

If the wire is supported on a messenger that has at least the breaking
strength of #14 AWG wire the reasonableness standard should serve as an
effective shield against that particular approach in a law suit. Be
aware that in electrical parlance, which is what the code is written in,
messenger supported means that it is continuously supported by another
means. It does not mean that it is suspended from some stronger support
at it's ends. To be messenger supported the entire weight and the
catenary strain of the support system would have to be born entirely by
a means other than the undersized conductor itself.

I am not a lawyer nor do I play one on local cable access television.
If you need advice about the most likely legal affects of an injury that
is caused by your amateur radio equipment you might want to patronize a
law schools legal clinic. The Professors that supervise such clinics
love questions like this because they take a fair amount of effort to
answer well. What you end up with is really high quality advice
prepared under the supervision of some of the best legal minds that a
person of ordinary means could ever get access to.

I've quoted the sections of the NEC which are applicable to antenna
conductor size below. Be aware that the NEC contains many more
provisions covering amateur radio stations specifically. It is worth
your time to obtain the use of the edition of the NEC that is adopted
for enforcement in your community and check your installation against
the provisions of the code.

--
FWIW YMMV
Tom Horne, W3TDH

"ARTICLE 810 Radio and Television Equipment
I. General
810.1 Scope.
This article covers antenna systems for radio and television receiving
equipment, amateur radio transmitting and receiving equipment, and
certain features of transmitter safety. This article covers antennas
such as multi-element, vertical rod, and dish, and also covers the
wiring and cabling that connects them to equipment.

810.11 Material.
Antennas and lead-in conductors shall be of hard-drawn copper, bronze,
aluminum alloy, copper-clad steel, or other high-strength,
corrosion-resistant material.
Exception: Soft-drawn or medium-drawn copper shall be permitted for
lead-in conductors where the maximum span between points of support is
less than 11 m (35 ft).

810.12 Supports.
Outdoor antennas and lead-in conductors shall be securely supported. The
antennas or lead-in conductors shall not be attached to the electric
service mast. They shall not be attached to poles or similar structures
carrying open electric light or power wires or trolley wires of over 250
volts between conductors. Insulators supporting the antenna conductors
shall have sufficient mechanical strength to safely support the
conductors. Lead-in conductors shall be securely attached to the antennas.

810.13 Avoidance of Contacts with Conductors of Other Systems.
Outdoor antennas and lead-in conductors from an antenna to a building
shall not cross over open conductors of electric light or power circuits
and shall be kept well away from all such circuits so as to avoid the
possibility of accidental contact. Where proximity to open electric
light or power service conductors of less than 250 volts between
conductors cannot be avoided, the installation shall be such as to
provide a clearance of at least 600 mm (2 ft).

Where practicable, antenna conductors shall be installed so as not to
cross under open electric light or power conductors.

[One of the leading causes of electrical shock and electrocution,
according to statistical reports, is the accidental contact of radio,
television, and amateur radio transmitting and receiving antennas and
equipment with light or power conductors. Extreme caution should
therefore be exercised during this type of installation, and periodic
visual inspections should be conducted thereafter. ] This is explanatory
material from the NEC Handbook and not part of the NEC.

810.14 Splices.
Splices and joints in antenna spans shall be made mechanically secure
with approved splicing devices or by such other means as will not
appreciably weaken the conductors.

[Conductor spans from antennas should be of sufficient size and strength
to maintain clearances and avoid possible contact with light or power
conductors. Splices and joints should be made with approved connectors
or other means that provide sufficient mechanical strength so that
conductors are not weakened appreciably, a condition that could cause
them to break and come into contact with higher-voltage conductors.]
This is explanatory material from the NEC Handbook and not part of the
NEC.

810.15 Grounding.
Masts and metal structures supporting antennas shall be grounded in
accordance with 810.21.

810.52 Size of Antenna.
Antenna conductors for transmitting and receiving stations shall be of a
size not less than given in Table 810.52.

Table 810.52 Size of Amateur Station Outdoor Antenna Conductors
Material Minimum Size of Conductors (AWG)
Where Maximum Open Span Length Is
Less Than 45 m (150 ft) Over 45 m (150 ft)
Hard-drawn copper 14 10
Copper-clad steel, bronze, or other high-strength material
14 12

810.53 Size of Lead-In Conductors.
Lead-in conductors for transmitting stations shall, for various maximum
span lengths, be of a size at least as great as that of conductors for
antennas as specified in 810.52." Copyright 2002 the National Fire
Protection Association.