[TowerTalk] Which type of cable for a crank-up tower?

[Jim Lux]

On 12/2/11 8:03 AM, K7LXC at aol.com wrote:
> In a message dated 12/2/2011 3:39:02 A.M. Pacific Standard Time,
> towertalk-request at contesting.com writes:
>
>>   I have an unidentified 65' crank-up tower, believed  to be of English
> origin.  It needs to be recabled.  The existing  (original) cable appears to
> be 5/16", but it might be 8mm or even 7mm (I am  not where the tower is, so I
> can't measure it exactly).  Definitely  bigger than 1/4".  The tower lives
> in a very salty, island  climate.
>
>>   I am trying to figure out what type of cable to use  - not which size,
> but which material and construction.
>
>>   The  easiest thing to find that seems appropriate is 5/16" 7x19
> galvanized  steel.
>
>>   But, I have read that these towers usually use 6x19  LC (linen core) -
> which I can find in plain steel, but not in  galvanized.
>
>
>      Read where? I haven't heard of it - especially  when it comes to
> towers.
>
>      All USA crank-ups that I know of use common  7x19" galvanized. Since
> the original is unidentified, I'd suggest  following the overwhelming use on
> Ameriacan crank-ups and use the 7x19 of  whatever size you need.
>
>>   1) Is galvanized the way to go in  this situation?
>
>      Only if it's going to be installed outdoors.  (That's a joke, son.) Of
> course use galvanized.
>
>>   2) Any  sense of which construction is most appropriate?  I assume 7x19
> would be  best if I can't find the 6x19 LC.
>
>      Yes. The 6x19 might be an English standard. It  sure isn't the US
> standard.
>

I think it depends on whether you are talking "wire rope" or "aircraft 
cable".. in the US, 6x19 is a wire rope:  a 6x19 is 6 strands each made 
up of 15 to 26 wires around a fiber core (FC).  There's a mention of a 
IWRC (Independent wire ropecore) which is a separate 7x7 wire rope used 
as a core, but it's still called a 6x19 rope.


  there's a 19x7 which is a double layer with 19 strands, each with 7 
wires. 12 strands right regular lay over a core of 7 strands with left 
lay. It's rotation resistant (I'm getting all this from southwest wire 
rope, inc technical data.. http://www.swwrinc.com and from
http://www.lexcocable.com/wire-rope.html)

the 19x7 is non-twisting and more flexible, of course.

That's all wire rope... if you get into aircraft cable, there's yet 
others...

7x19 and 7x7, which are 7 strands (one in the middle, 6 around) with 
various numbers of wires making up the strand.  Apparently not always 
19, for the 7-19.. they change the size AND number of wires to change 
the size of the cable.

and if that weren't enough, I found what's called ASTM A603 Structural 
Bridge Rope (recommended for fixed installations.. bridges, tower guys, 
etc.) which seems to be either 7x7 or 6x25 construction.


---

take home:  by just looking at the cable (generic term), it's probably 
pretty tough to tell exactly whether it's wire rope, aircraft cable, or 
something else. Even if you splay it out and figure out the stranding 
and lay, you still would have a tough time.

The OP mentioned a 6x19, which is almost certainly a wire rope of medium 
flexibility, and since it's designed for hoisting kinds of applications, 
I can see where it would be used for a tower.

Of course, aircraft cable is designed for repeated flexing (around 
pullies) on a second to second basis.  Whether that's needed for a crank 
up tower?  I suspect you give up some strength compared to a wire rope 
of the same diameter (and if you go to stainless steel, you certainly 
give up strength compared to galvanized wire), but does it make any 
difference in the tower application?  I don't know how much design 
margin there is.

5/16" 6x19 FC wire rope has a nominal strength of 5500 lb. 5/16" 6x9 
IWRC is 9160 lb for the same material 10,450 lb for "improved plow steel)

5/16" 7x19 Aircraft cable is pretty big (right at the top of the table) 
and has a breaking strength of 9800lb in galvanized and 9000 lb in 
302/304 SS, 8290 in 316SS

Just guessing, I'd say the run of the mill tower thing is probably using 
wire rope..cheap, strong, not like you're using to move the ailerons 
every few seconds.