[TowerTalk] US Tower tubular crankups

[K7LXC@aol.com]

In a message dated 6/4/01 4:41:44 PM Pacific Daylight Time, kahager@gis.net 
writes:

> Considering the purchase of a used 7 yr old US Tower MA40 Tubular style
>  crankup and have been told by the company that the cables need to be
>  replaced approx every 3 years depending on the climate by a professional
>  installer.  
>  Has any user of this type of tower had to replace the cables on
>  their tower and if so what was the expense?  Is 3 years the approx life 
span
>  for cables on a crankups generally speaking or can you expect to get more
>  life out of them.  I suppose the company is playing it safe(liability wise)
>  when  making this recomendation.

    I didn't see any responses to this so better late than never.

    Yes, the company line is replace the cables every 3 years. This is their 
"weasel clause" in case anything happens they can 'weasel' out of any 
responsibility.

    The real world situation is that yes, cables do need to be replaced 
occasionally. How occasionally? You need to replace the cables if 1) there is 
deep rust - not just surface rust which is no big deal. 2) Replace the cables 
if there's obvious damage. This would be a permanent set that the cable has 
taken somewhere. This is where the cable is obviously bent or not in its 
normal straight orientation. 3) You should replace the cables if you have 
broken strands. Wire rope cable industry standards have a 6/3 rule. That is a 
cable should be replaced if there are more than 6 strands broken (crank-ups 
normally use 7/19 cables which is 7 bundles of 19 strands each) or 3 breaks 
in one strand. Since you have a tower where the cables are basically hidden, 
they are not easily observable so you need to figure out how to do it. 

    To replace (or inspect) the cables on this tower, you have to get it 
horizontal and then pull the sections apart. The sections aren't that heavy 
so a couple of guys can do it. You just need the room to do it. Also 
disassembling an existing antenna array isn't very palatable for many people. 

    Since you're going to be buying it and then bringing it home, that'll be 
a good opportunity to do the aforementioned disassembly/inspection. If the 
cables appear to be fine (and they most likely will be unless the tower was 
in a hostile environment), then use a good cable lubricant like PreLube 6 
(available from  <A HREF="http://www.championradio.com">Champion Radio 
Products</A> and recommended by wire rope manufacturers) and then put it up.

    To prolong cable life, you can do several things. First, exercise the 
tower a couple of times a month. That is, run it all the way up and down a 
couple of times. Next, don't use the same spot every time for when the tower 
is extended or retracted. It's real easy to just use the limit switch spots 
but over time the cable will take a set at those points. It's better to 
spread the cable work over different spots than the same one all the time. 
And of course do an inspection and use a cable lubricant twice a year. 

Cheers,   Steve    K7LXC
Tower Tech
Factory authorized US Tower installer

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