Two of these strands are not like the others... (with new pictures)

[rjlittlefield]

I was splicing some wires today and found it surprisingly difficult to get the insulation off.

After simply struggling with it for a while, I took a closer look.

To my surprise, the real problem was not the insulation, it was the copper!

As far as I can see through a stereo scope, two of the wire strands actually consist of an exquisitely fine helix of copper foil, wrapped around a plastic core.

The diameter of the yellow insulation measures only 0.82 mm, which makes the diameter of the wrapped strand around 0.23 mm. The thickness of the foil is impossible to see accurately, but it seems to be on the order of 0.02 mm or less. The stuff is small!

The cable is nothing fancy, just a 2.5 mm stereo male/male, visually similar to https://www.amazon.com/gp/product/B09XXFYGXP?th=1 . I think it came as a flash sync cable with some inexpensive RF triggers.

Anyway, I am not familiar with this type of stranded wire.

Can somebody who is, please tell me about it?

--Rik

(Edited to change title)

[Sym P. le]

Tinsel wire

(Just a lucky google hit)

[rjlittlefield]

"Tinsel wire" -- an excellent name and a good reference. Thanks for the handle!

But...

I am still puzzled by this particular cable, which combines 2 tinsel wire strands with a half dozen ordinary solid strands in each of its three conductors (only one shown here).

It's almost like the designers have planned for some sort of graceful degradation, with the tinsel wire for long life but low current capacity after the solid strands have broken.

This seems a strange design.

Are they maybe targeting some sort of dual-spec cable that has either higher current capacity if not mechanically stressed, or longer fatigue life if not electrically stressed?

--Rik

[Olympusman]

It is my understanding that current travels on the surface of wires, so this may a means of effecting more efficient transmission.

Mike

[DavyC]

I am still puzzled by this particular cable

Rik,
The spiral copper wrap provides ‘screening’ to minimize Electro-Magnetic Interference (emi)
Helps prevent external emi affecting the transmission of signals within the cable
and prevent emi produced by currents within the cable interfering with sensitive equipment in the vicinity of the cable.
D.

[rjlittlefield]

Lots of interest I see. Thanks for all the suggestions!

@Olympusman, that's the "skin effect". It gets important at high frequencies. There's a calculator at https://www.allaboutcircuits.com/tools/ ... alculator/ . For a handy reference point, standard Cat-5 network cable, designed for use up to 100 MHz, still uses single-strand conductors. But the cable I'm showing is intended for low frequency use, where ordinary strands would work fine from an electrical standpoint. In fact the cable I was splicing this with, visually quite similar except for being longer and straighter, has ordinary strands.

@DavyC, I expect you're thinking of braided shielding, like in coax cables or shielded audio cables, as described at https://en.wikipedia.org/wiki/Shielded_cable . The problem with that idea here is that there's nothing inside the wrap to be shielded -- it's just a helix of copper foil wrapped around a plastic core. Some audio cables are shielded (the good ones!), but this particular cable has nothing of the sort. It doesn't even twist the conductors together (unlike Cat-5 cable, which has one twist about every 15 mm).

--Rik

[Sym P. le]

Rik, you've referenced a TRS cable at amazon. Inherently, I would expect three channels. Are the solid copper twisted lines isolated from the tinsel wire pair or perhaps the individual wires are coated and the manufacture is confident enough that further isolation is not warranted.

Perhaps a photo of a clean cut cross section would be helpful.

[rjlittlefield]

Rik, you've referenced a TRS cable at amazon. Inherently, I would expect three channels. Are the solid copper twisted lines isolated from the tinsel wire pair or perhaps the individual wires are coated and the manufacture is confident enough that further isolation is not warranted.

Perhaps a photo of a clean cut cross section would be helpful.

Sorry, I left too much undescribed. Yes, it's a TRS cable (tip/ring/sleeve). The cable contains three separate insulated conductors, one each in red, white, and yellow, all surrounded by a black plastic shell. The pictures above show a cut and stripped section of just the yellow one, which happens to connect to the sleeve. All the copper shown in the first two pictures comprises a single conductor. The red and white (tip and ring) are similar, but separate from the yellow and from each other.

In case you're wondering, the splicing was to create a two-headed extension cable: two plugs and one jack, with all the tips, all the rings, and all the sleeves connected together. The function is to let two Canon cameras be controlled by a single remote trigger so as to fire at nominally the same time.

--Rik

[Sym P. le]

I suspect it has to do with passing a spectrum of frequencies typically found in audio signals. Check out the wiki article on Litz wire as well. This leads me to believe each of the strands would be lacquer coated. Are the solid copper strands all the same gauge or various. Also, a link explaining advantages of square vs. round wire, again with a view to performance enhancement in the higher frequencies. At the same time, the tinsel core may offer some durability enhancements for the package.

Lastly, a pdf on how to solder tinsel/litz wire.

[DavyC]

Sorry, I left too much undescribed.

Rik,
If there is no electrical screening/ legacy component to the twisted copper sheathing,
then it's maybe there for physical structure/protection of the finer underlying wires.

D.

[rjlittlefield]

I suspect it has to do with passing a spectrum of frequencies typically found in audio signals. Check out the wiki article on Litz wire as well. This leads me to believe each of the strands would be lacquer coated. Are the solid copper strands all the same gauge or various. Also, a link explaining advantages of square vs. round wire, again with a view to performance enhancement in the higher frequencies. At the same time, the tinsel core may offer some durability enhancements for the package.

Thanks for the link to Litz wire. When I was young I used to see that stuff in radios, but I had forgotten about it. The explanation provided by the Wikipedia article is far more detailed than anything I had read previously.

Regarding the wire that prompted this thread, I finally had time to investigate further and make some better pictures.





The cross-sections below were cut by running the insulated conductors into holes in wood that were just barely large enough to accept them (#66 = 0.84 mm), then filling voids with CA glue prior to shaving off the ends with a fresh #10 scalpel. The scrape marks on the copper are from the manufacturer's sharpening scratches on the scalpel. Crossed eye stereo pairs...







In the photos I do not see any signs of lacquer coating, and I confirmed that gently touching any of the copper strands at any point with an ohmmeter shows continuity.

So nope, no insulation -- all of the strands are connected together everywhere they touch. Following the explanation in the Litz wire article, I think this argues against any frequency-dependent purpose.

I was interested to see in these photos that the plastic core of the tinsel wire strands is itself stranded. That would be a good contribution to flexibility, but the surrounding solid wire strands and especially the colored insulation make the cable overall quite stiff.

I'm still thinking that the tinsel wire parts are for resistance against complete breakage. But I'm also still eager to hear other possibilities.

The replacement cable that I bought from Amazon following the earlier link turned out to use ordinary stranded conductors, not tinsel wire. Overall stiffness of the cable was similar.

Photographed with 2X, 5X, and 10X Mitutoyo M Plan Apo objectives, and Raynox DCR-150 tube lens, on Canon R7 camera, two Jansjö LED's through hemispherical painted diffuser.

--Rik