On 8/2/2011 8:24 AM, John S wrote:
On 8/1/2011 7:52 PM, Jim Lux wrote:
On 7/31/2011 3:26 PM, Owen Duffy wrote:
John wrote in :


Maybe because NFPA 70 costs $150 US?


Yes, standards are expensive things and it is a frustration when
researching.

Anyway, NFPA makes recommendation on the wires for ham antennas
specifically, and it may be binding in some places.

I suspect the reason for ignoring it is that the advice is unaccepable
to most hams.

That said, it does seem over the top in some areas, and is hardly
comprehensive in its thinking. For example, the prescription for
feedlines seems to not be aware of the existence and use of coax.

You refer to the "continuously enclosed metallic shield", I suspect.


I guess it is these gaps that give critics the basis for arguing against
the whole thing.

Anyway, in respect of antenna wires, it does not 'permit' annealled
copper or other low strength materials, and it 'requires' a minimum
conductor diameter of #14 for up to 150' span.

They may have had in mind the risk to persons and property where low
strength conductor are broken in high wind and make contact with power
lines.


That is precisely why. (ice loads, too)

NFPA (according to what you posted) requires heavier gauge wire for
transmitting than for receiving. Transmitting makes the wire weigh more?


An interesting observation. You'd have to go look at the history of
that article in the code to find out why. It's not impossible that they
were following standard commercial installation practice/recommendations
back in the day, and it was "acceptable power loss" related. (the wire
sizing for AC branch circuits is based on tolerating a 2% voltage drop,
not overheating of the conductor)