Greetings fellow TTs:
As my new tower gets closer to going up (still have to clean out the bottom
corners of the foundation hole, but it's been over 100 deg. F here lately) I
am thinking of my old tower's (UST MA-550MDP) nice circular foundation. It
is in the front of the house and in an ideal location for a flagpole. I've
been looking at the streetlight poles the city uses. They are
tubular/tapered, starting at about 4" diameter at the bottom to maybe 2" at
the top. They have a four-bolt mounting pattern almost identical to the
MA-550's rotor base. They look like they would make a great flagpole and a
lighted one at that. Any idea where I could find one of those critters?
You must buy in large quantity from the manufacturers, so that doesn't work.
I've tried calling the city to see if they have surplus. No luck. I'll try
some other local cities and the county, but maybe someone on here has an
idea? I'm looking for something in the 30' range.
Thanks & 73 - JC, K0HPS
[mailto:firstname.lastname@example.org]On Behalf Of Bill Aycock
Sent: Wednesday, July 19, 2006 2:00 PM
To: Nick Pair; Towertalk@contesting.com
Subject: Re: [TowerTalk] braid and high current
Pardon me, but this is the biggest collection of garbage on this subject
that I have seen. The braided copper conductors I have seen in explosives
storage were about 1/2 inch in diameter, and were braided to allow limited
flexing on installation. The individual wires were at least #12, and more
likely (from appearance) #10. Also, Army Ordnance, at least, thought they
were there for lightning grounding and dissipation, not just to calm the
fears of the peasants. Next time, get some facts before expounding .
At 11:17 AM 7/19/2006 -0700, you wrote:
> The first problem with braid is that the stuff forms a coating of
> copper oxide around each strand that is nonconductive. This coating makes
> each wire like a individual conductor with a resistance according to its
> gage. Now think of the flexing due to vibration, heat cycling, or any
> other thing which will cause the strands to rub against each other thus
> breaking the copper oxide surface. The crossover points of the braid will
> be alternatively be conducting and then reoxidizing to nonconducting
> state. This makes all the strands at different resistances which when the
> 20,000 to 200,000 amp surge hits them will cause some of them to take
> more of the current than others and vaporize. An avalanche effect occurs
> and you have meltdown and arcs.
> Second we have the idea that all the current will travel on surface
> with the skin effect. This is true for normal current amounts but at the
> current levels of lightning there are not enough free electrons at
> accommodate the current flow and the conductor depth comes into account.
> If not enough depth is available the current has to flow outside of the
> conductor in a arc as there is no where for all those electrons to go.
> The use of braided strapping to protect ammunition was to prevent a
> static discharge from detonating the charges not the high current of
> lightning. In the workers minds they thought it was for lightning but all
> you can do with lightning is shunt the current, not stop flow. Even if
> you shunt 99% of current there is enough voltage to arc at even micro
> amps which is enough to make fireworks out of your munitions. The only
> safe place was inside of conductive box with lid closed. (i.e. ammo
> boxes, metal lined bunkers, etc.)
> That leaves us with either large stranded (each strand #12 or
> larger) or solid conductors. Even solid has enough flex to allow a
> fold-over to work if you disconnect(or never use ) the ground opposite
> the hinge.
> Save your braid for your indoor station ground applications.
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Bill Aycock - W4BSG
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