I picked up a couple new basket cases at the local junk dealer and while giving them the once-over a question about wiring came up. What are the pre-war power cords and internal connection wires made of? They are silver colored under the insulation and when cut still do not appear to be copper. They also feel too heavy to be aluminum.

Power cords: early 30's sets were stranded copper wire covered with fabric-covered rubber and cloth-sheathed (outer covering). Later 30's sets used stranded copper wire with molded rubber overcoats. Since both cord types use natural rubber, both types dry out and crack. (Vinyl will age and crack, too, but it seems to be much more durable than rubber).

Hookup wires: rubber, cloth, or cloth+rubber insulation, usually copper core wires with tin plating.

:
:usually copper core wires with tin plating.
:
Our early 1950s house has solid copper wiring that is tinned. I never understood the thinking behind that - such wires were never connected by soldering. For radio hook-up wire, tinning makes sense.

One Internet source I've found holds that rubber-insulated copper wire was tin-plated in order to prevent a chemical reaction between the sulfur used in the rubber vulcanization process and bare copper. Modern house wiring uses a non-rubber plastic insulation which is nonreactive with copper- therefore no need for tin plating to serve as a "buffer" layer. Sounds reasonable to me, but I can't vouch for its factual basis.

Thanks, makes sense.

I wonder about rubber-insulated stranded copper wire? Was it tinned?

Don't have any handy right now to check, but I would guess that the wire core had a fabric overwrap to separate the copper strands from the rubber coating.

Several years ago, when we moved into our early '50s house, I was thrown for a loop by the tinned wiring. At first I thought it might be aluminum, but I quickly realized that Al wire was not used at that time. Later, an old-time electrician set me straight.

The inside house wiring is fabric-sheathed, sort of like modern Type NM. The individual conductors probably are rubber insulated - the insulation adheres to the wire, and must be stripped with a knife.

Our 60-year-old underground circuit for our yard lights failed some time ago. It was just plain "building wire," probably rubber insulated, direct buried with no protective sheath or conduit. It's a wonder it lasted so long.

Our 100-A underground service from the utility was originally rubber-insulated conductors pulled in a steel conduit. It was working fine, but I decided to replace the service with a modern 200-A buried feeder in plastic conduit.

I have a bit of experience with old knob-and-tube wiring, which worked fine, although new installations are prohibited, of course.