I just finished replacing the top set of guys on my 127' 160m vertical. Big
Grips were used with the strain insulators, replacing the cable clamps used on
the old guys. Some of the information I gleaned from this project is not widely
published and might be useful to others.
A major problem amateurs may have using Big Grips is lack of installation
instructions. About 20 years ago and again about 5 years I purchased grips from
Texas Towers, and more recently from Hill Radio in Illinois. In all three
orders the grips arrived with no instructions whatever. I was eventually able
to download instructions on-line from the PLP website, but I lacked internet
access 20 years ago and worked by intuition. I don't know if this is the fault
of PLP or of the vendors who re-sell the product, but you would think that any
product that requires a specific installation procedure critical to safety, as
do these grips, would come with instructions. A mistake I made 20 years ago,
precisely due to lack of instructions, was to use the first set of crossover
marks instead of the second when installing grips on type 502 insulators. They
have worked satisfactorily, although one insulator broke a few years later, but
I couldn't determine if the Big Grip installation had anything to do with it,
or if one of the used insulators acquired from the power company happened to be
damaged or defective.
The installation instructions I downloaded from PLP recommends splitting each
leg of the grip into two sections up to the crossover mark before installing
them on the cable, and then wrapping each one of the four resulting sections,
one at at time. This makes the job easier and the wrapping comes out more
uniform, than when the whole legs are wrapped in one piece. One precaution I
would recommend is to be extremely careful when splitting the legs, since the
glue used with the grit material sometimes tends to stay in one piece and pull
off one of the split sections as they are separated. There is no mention of
this in the instructions. I used a small knife to help separate the grit
material whenever I noticed this was about to happen.
I suspect that's the reason PLP recommends discarding a set of grips after
they have been removed and re-installed on the cable more than two times; each
removal and re-wrapping likely results in some loss of grit material.
After replacing the broken insulator and employing a new set of grips (this
time using the second crossover mark), I examined the old set of grips, and the
grit substance still looked intact. I see no obvious reason why they don't
recommend re-using grips that have been in place longer that three months, but
to be on the safe side I used a fresh set with the new insulator. Perhaps the
grit material deteriorates after a certain length of time.
The PLP instructions are somewhat ambiguous in explaining the first and second
crossover points, making no mention at all of use with insulators. I became
aware of the correct procedure, after the fact, only from third party
recommendations.
A precaution when using Big Grips with strain insulators is to make sure the
contour of the hole in the insulator closely follows that of the U-bend of the
Big Grip. I talked to one of the engineers at PLP, who told me that Big Grips
have failed when used with improper insulators. Apparently, "johnny balls" are
no longer manufactured in USA, and he said problems have occurred with ones now
made offshore in places like Brazil and China, that may not be shaped to
precisely seat the Big Grip. If the stress of the load is not distributed
uniformly over U-bend but concentrated at one or more isolated points, the
brittle nature of the wire used to make the grips may cause stress fractures to
appear in a strand, possibly resulting in catastrophic failure. He recommended
staying with cable clamps if the insulator doesn't exactly fit the contour of
the grips.
Don k4kyv
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