Lamp Repair using a Rigger's Constricting Knot

Yesterday, I noticed that the lamp hanging over the kitchen sink was no longer hanging by the woven polyester cable sheath (which is intended
to carry the weight of the lamp fixture) and was now hanging by the electrical wires. Which were coming undone - the terminal screws had already backed out a bit. Not good.
It turned out that over the five years since installation, the cable sheath had wiggled out of the crimped strain relief ring ferrule at the lamp end of the cable. The ring was crimped by being crushed into a (US) football shape, and one end had broken, reducing the clamping pressure on the cable. Discarded the ferrule. But what to replace it with?
In the thread on corrosion when aluminum and stainless steel are in contact, I had mentioned the Rigger's Apprentice book, and their recipes for lanolin as a corrosion preventer.
This same book talks of "constrictor knots", used to repair such things as split tillers. Hmm. This could work.
So, I replaced the metal ferrule with a double constrictor knot made of nylon cord, all well daubed with Pliobond rubber cement. We'll see how well this works, but it ought to be permanent.
Joe Gwinn
Ref: "The Complete Rigger's Apprentice - Tools and Techniques for Modern and Traditional Rigging", Brion Toss, International Marine, Camden, Maine, 1998 McGraw-Hill.
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On Dec 8, 2015, Joe Gwinn wrote

Followup: It failed already - the constrictor knot just slid off the cable. Probably due to the heat of the lamp softening things. I?ll probably make some kind of tight-fitting swage collar of metal.
Joe Gwinn
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On Wed, 09 Dec 2015 10:14:48 -0500, Joseph Gwinn


Have you considered NOT hanging the lamp by the cord? It has always seemed to be a short waiting to happen, as the knots slip out, knocking off the poorly applied wire nuts...
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    [ ... ]


    Well ... there is the "Underwriter's Knot", which used to be used to keep wires from pulling out of fixtures -- back before things like the Heyco strain relief nuts replaced grommets. (And the knot did not even require a special tool, unlike the Heyco strain relief nuts.
    O.K. This site gives a video:
    <
https://www.youtube.com/watch?v=KHRaRRWW34w

    And this one is pure text:
    <http://www.howtodothings.com/home-garden/how-to-tie-an-underwriters-knot
    Enjoy,         DoN.
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On Wednesday, December 9, 2015 at 8:39:21 PM UTC-5, DoN. Nichols wrote:

I wonder how many lamps are strain-relieved by underwriters knots. Tens of millions, perhaps? This was one of the first 'electrical' things I ever learned.
Meanwhile, I watched the video, which was perfect. Then I watched another about the 'truckers hitch.' That's a new one on me. I always use ratchet strap tiedowns, but I do like this knot.
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I do know of underwriter's knots. It's possible, but I would push the sleeve back first, tie the knot, and slide the sleeve back over the knot, making a bump in the sleeve.
Joe Gwinn
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On Wed, 09 Dec 2015 10:14:48 -0500
<snip>

.

ly make

Maybe use some heat-shrink tubing over the knot/area?
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On Wed, 09 Dec 2015 10:14:48 -0500, Joseph Gwinn


Would one of these do the job?
http://myoasisofficesupplies.com/test/productimages/double-clip-15mm-small-.jpg
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Yeah. I used know a Rigger like that. I think his first name was Jury.
Sorry. Couldn't resist.
Steve
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wrote:

He had another brother, Jerry, who used to MacGuyver things in der Deutchland back in WWII.

Ditto.
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    [ ... ]

    [ ... ]

    Hmm ... do you happen to have crimpers for coax RF connectors? Perhaps one of the sleeves which go around the shield to crimp it to the body of the connector would work -- if the size is right. I would probably try to turn up a sleeve to go inside the jacket of the cable so there would be something for the round crushed to hex ferrule to press against.
BTW    You can still find Pliobond somewhere? I haven't seen it for     years, and have to use the alternative rubber cement brand.
    Good Luck,         DoN.
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I do have such crimpers and can make a ferrule, and was considering doing just this. Maybe wetted with epoxy before crimping.

I think so, although Goodyear sold the line. I have a half-pint steel can with brush, bought from McMaster-Carr in May 2012, of "Pliobond 25". It is made by The Ruscoe Company of Akron, Ohio. The product code seems to be PBC-25-LV. The Pliobond trademark appears to be owned by Ashland, Inc.
I also have "Super Contact Cement" (cat no 8336) made by MG Chemicals. This also seems to be pliobond rubber cement, but without the trademark name.
Joie Gwinn
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On Tuesday, December 8, 2015 at 6:28:11 AM UTC-8, Joe Gwinn wrote:

Sounds good, and it's likely the rubber cement won't attack the materials. I'd have used hotmelt glue, and instead of a knot, just a wrap or two of a nylon tie-wrap. Anything you can get tight, that stays tight, should work at least as well as the original did.
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no

of

Its a kitchen, so unless you never eat fried or baked food, the chances are the insulation and cable jacket was contaminated with condensed food oils and greases. A constrictor knot only works if its done in cord of an appropriate thickness on a clean rounded surface, and it *MUST* be pulled up tight. If the knot isn't pulled tight or the cord is too thin (or surface too flat) so there isn't enough pressure on the crossover or the surface is too curved so the ends are free to shift it will fail. Also Nylon is particularily slippery. To have stood a good chance of it working, you would have had to degrease the cable jacket, and use cotton or hemp cordage, or unwaxed polyester then locked it with a drop of superglue.
As-is: clean the jacket with hot water and detergent. Dry and wipe with alcohol. Reinforce with a short length of adhesive lined heatshrink, taking care NOT to overheat the jacket while shrinking it then use a nylon cable tie looped round twice and pulled tight with pliers.
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All those things were done, except for the crazy glue. The reason for pliobond is that it is solvent-based, and quite tolerant of oils.
What I think happened is that the heat softened the insulation on the wires, causing loss of clamping pressure, and increasing creep.

The heat shrink could work, but I think I'm going with a metal clamp. I did some google research, and the best cord camp is a thick-walled metal tube with a perpendicular round-face set screw. This is a standard design.
Joe Gwinn
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I'm going to make a metal clamp ring, modeled on the commercial cord clamps.
Joe Gwinn
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On Dec 10, 2015, Joe Gwinn wrote

I have made and installed a machined 0.5? round brass sleeve with a perpendicular round-face 1/4-28 setscrew in the center, used to clamp the cable. The braided sleeve is very rough, and the sleeve fits over it perfectly. This is one standard design, most often implemented in plastic. We will see how long this lasts. Should be forever.
Joe Gwinn
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