Some insulated multistrnd copper wire is pre-tinned and a lot is not.
What is the purpose of pre-tinned wire? As far as I can see the advantage is that the copper core doesn't oxidise which means the wire can be soldered or fixed to a terminate with only minimal cleaning.
Sounds like a good thing to me, so why isn't almost all wire pre- tinned?
Is cost really so different?
Does the tinning-coating replace where copper would have been in the overall wire and tinning is of higher reistence?
:Some insulated multistrnd copper wire is pre-tinned and a lot is :not. : :What is the purpose of pre-tinned wire? As far as I can see the :advantage is that the copper core doesn't oxidise which means the :wire can be soldered or fixed to a terminate with only minimal :cleaning. : :Sounds like a good thing to me, so why isn't almost all wire pre- :tinned? : :Is cost really so different? : :Does the tinning-coating replace where copper would have been in :the overall wire and tinning is of higher reistence? : :Is flexibility affected?
As you surmised, the answer is cost. It is not the cost of the tin itself but the additional process and handling which adds to the complexity of production. The copper conductor wire gauge is not made smaller where tinning is not applied and the added few microns of tin would not affect resistance/unit length by any significant degree. Flexibility is not an issue.
I think that manufacturers realise the majority of termination methods used today rely on crimping or soldering while the copper conductors are clean. Tinned conductors are an advantage where the conductors are secured by screws or wire-wrap although less so for the latter. Insulation displacement techniques are not a problem for untinned conductors.
I think the reason for silver-plated teflon wiring is mostly milspec compliance (and the follow-ons that include the mispecs.) The real question is, why is it in the milspec? Certainly WWII and Korea influenced milspecs a lot to focus on fungus-proofing, and Teflon had some advantages back then when the other insulators were not so fungus resistant. At the same time, other insulating materials can turn copper or even tin-plated copper inside the insulation black with a kinda sooty residue (common on Romex from the 50's-70's for example). It seems to me that silver-plated teflon was a kind of knee jerk reaction to these two issues, a belt-and-suspenders-cost-is-no-object approach to a pretty mundane but really fundamental issue.
It's a real joy to work on ex-military equipment with Teflon cable assemblies. Compare it to other consumer or less-speced industrial stuff from the same era with PVC-type insulation, where you flex the cable a little bit and the insulation cracks and falls off leaving bare wires.
Yes, Silver is one of the few metals that has a lower resistance than copper, but oxidises easily so silver should be covered, PTFE is one of the best coverings.
My guess is that tinned wire is soldered more easily even after much exposure to unfriendly environments. You do not have any copper oxide to remove. Any crap in the tin flots away and new solder flows in under such crap.
My understanding is that the Teflon-insulated wire uses silverplating for a couple of reasons, related to the high melting point of Teflon (and thus the high temperatures to which the wire is exposed when the Teflon is melt-extruded onto the conductors).
The old-standard tin/lead tinning material can't be used in this high-temperature environment, as it would be melted by the heat of the Teflon extrusion, and would fuse a stranded-conductor wire into an inflexible single strand.
Not tinning or plating the wire would leave the surface of the copper exposed to high temperatures during the extrusion... I suspect that it would oxidize (if there's any free oxygen in that environment... dunno about that) or might react with the polymer. Even if it didn't react at that time, oxygen would infiltrate the wire at the cut end (albeit slowly) and the last few inches of the wire might end up with a significant amount of copper oxide on the conducter surface.
Silver-plating protects the copper from oxidation (I gather that silver oxide is somewhat easier for fluxes to deal with?) and the silver doesn't melt at the Teflon extrusion temperature.
I don't believe that the silver plating is thick enough to give the wire a significant conductivity advantage over pure copper, even at RF frequencies.
I checked looked at a spool of about #20 stranded wire. It does look very shiny like silver. I thought it was odd looking at it. its made up of a tightly twisted center section and a loosly woven outer section around the inner section. The TFE is almost a fluorescent blue. Neat stuff. 19/32 strands.
That's what I would have thought too. But if pre-tinned (plastic insulated) wire is so useful in this respect then why isn't pre- tinned found more often?
I'm not thinking of the use of wire at RF frequencies but as an interconecting wire.
I haven't managed to compare the cost of pre-tinned wire identical plain copper wire but I don't ever recall seeing tinned wire and thinking it was unexpectedly expensive. Has anyone got any info from making this comparison in the past?
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