You're overthinking this. 10% of breaking strength pretension
recommendation is not critical in most ham cases. It's a very general
ballpark figure. On towers that are heavily loaded, pretensions can be a
little more important. I see anything from 8% to 15% specs for
engineered towers at 60°F. Depends on many factors.
BTW, SS guy wire is generally rated for slightly *less* breaking
strength than galvanized EHS of similar construction.
Just figure 400 lbs pretension in either case for 3/16".
73, Steve K8LX.
On 7/25/2021 4:04 PM, Ken Alker wrote:
If my conclusions are correct, the chart appears to be based upon the
breaking strength of a different type of wire than one would use for a
tower. The chart appears to be based upon stainless steel cable (for
sailboats) rather than zinc coated cable (for towers). The SS cable has
a higher breaking strength, hence, using the Loos would mean one would
over-tention the guys on a tower if using the % scale, rather than the
LBS scale.
--On Sunday, July 25, 2021 3:49 PM -0400 john@kk9a.com wrote:
Why are you concerned with the Loos gauge's breaking strength chart? I
just use the table to set the guy wires to the recommended tension
(usually 10% of its breaking strength).
John KK9A
Ken Alker ka6ken wrote:
I'm new to this, but did a lot of research and found that the Loos PT2
appears to be calibrated for wire with a breaking strength of 4545-5000
lbs, while the Rohn 3/16EHS500 wire has a breaking strength of 3990 lbs.
I assume, based on specs on various types of wire rope found at
<http://www.wcwr.com/catalog/webcat.pdf>, that the Loos PT2 is calibrated
more for 1x19 Stainless Steel type 304 wire rope used for sailboat
rigging (4700 lbs) rather than zinc coated 3/16EHS500 (3990 lbs). Here
is my math based upon the chart found on the Loos gauge (from the web
site quoted by Tim, below):
LBS % LBS/%
---- -- -----
240 5 4800
300 6 5000
420 9 4666
500 11 4545
640 14 4571
840 18 4666
1030 22 4681
1240 26 4769
In conclusion, perhaps one should pay more attention to the "LBS TENSION"
portion of the Loos chart than the "% BREAK STRENGTH" if using the Loos
for 3/16" EHS (assuming it deflects in the same way that the sailboat
wire rope deflects), or one may overtension their guys. (Although,
perhaps the error when tensioning to 10% of breaking strength when
tensioning to 400lbs, or 600lbs in the case of Phillstran, isn't big
enough to worry about?)
Even then, however, I'm very curious as to why the Loos numbers are all
over the map (4545-5000) rather than consistent at one breaking strength;
it is not just rounding error since their "LBS TENSION" appears to be
+-10 lbs.
Ken, KA6KEN
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