copper oxidation with air insulation

[jonsson]

Hi, i wonder how copper will oxidate with only air as insulation, for example with only cotton or a teflon tube?

 

[JonSnell Electronic]

Back in the days of wooden conduit for single wire house wiring, (pre 1950 in the UK), the wire was insulated with cloth but was always tinned.

 

[rayma]

Hi, i wonder how copper will oxidate with only air as insulation, for example
with only cotton or a teflon tube?

Definitely, copper wire must be tinned during manufacture to prevent oxidation
from the oxygen in the air.

 

[PRR]

House wire (US) is never tinned(*). It oxidizes when hot-drawn so they run it through a "reducing furnace" where excess carbon eats-off the oxide and makes it pretty. In the house, over the years, it oxidizes, sure. In dry work it does not grow green-scuzz. The usual house-wire connectors use large pressure to break-through the oxide and this is rarely a problem(**). For soldering, old wire must be scrubbed or scraped to break the oxide so flux and solder will bond.

(*) Except under old rubber insulation, where the sulfides would quickly darken and eventually eat the copper.

(**) Unlike aluminum wire, where the tough insulating oxide resists ordinary pressure connectors and leads to trouble; little trouble in large gauges on proper connectors professionally cleaned and treated against oxidation.

 

[DF96]

Old copper in dry conditions just goes a dull brown colour on the surface. No harm done by this. So yes copper will oxidise, but no it doesn't matter.