Tinned CU or AL

I couldn’t tell if the cloth covered wires were tinned CU or AL. The home was built in 1940. Can anyone ID the conductor material positively?

I belive AL branch circuits (#12 size) weren’t avail till the 70’s.


Wires wrapped in cloth (circa 1940) are most likely Copper.

Here is the pic.


Aluminum wiring has a very distinct color.

When I was a Rookie, it was hard for me to differentiate aluminum wiring from tinned copper. Now that I’ve seen many aluminum wires, I spot it immediately.

This is what your looking for…

“Click to Enlarge”

Those are neutrals.

Where are the branch wires?

Them be tinned copper. . .

I told the client that I was 95% sure they were tinned copper, but that an eletrician could confirm for certain. There were plenty of other reasons to have an electrician out.

David, the insulation was inserted far enough into the breakers that I could not see any of the conductor material.

Was there any aluminum branch circuit wire with cloth insulation?

Hi to all,

here is a “rule of thumb” that seems to work, if the conductors are cloth/rubber covered it will be tinned copper, if the insulation is plastic it will be Aluminum.

I have never seen tinned copper with a plastic insulator, or Aluminum with cloth/rubber. By the time Aluminum single stranded conducors came to the market (mid 1960’s) the manufacturers were using plastic insulators.



Thanks Gerry. I will file that little tidbit away.

Gerry, there was at least one manufacturer that was using a silver colored copper conductor in PVC insulation with a blue jacket in the late 60s/70s. This is the TW type NM (not b). I found it in my house. The interesting thing about it is the black conductor is a deep copper color and it is the neutral that is silver colored. I suppose that was seen as a safety thing since it matches the coloring of the binding screws on some devices. I will dig around and see if I still have any of it in my junk wire pile. I yanked it all out of the house since the actual installation was really nasty (overstuffed boxes ,splices just twisted and taped etc) and since it was still 60c wire. In a Florida attic that is really pushing the derating limits.

That sounds like some of that Phelps/Dodge cable. It would be neat if you had some of that to post a picture. I run across it once in a blue moon. I can’t remember that last time I’ve seen tin plated copper with thermoplastic insulation. Gerry’s rule of thumb is still vaid, because it is very rare to seen tin plated copper with plastic insulation.

I’ve got it in my home circa 1955