Aluminum or tin coated copper wire??

Inspected a home yesterday, built in 1942, that at first glance appeared to have some single strand aluminum wire in some areas feeding out of an old fuse sub panel. (The main panel has been recently upgraded to a 200 amp service). Then I noticed that at some connections where the outer coating had been scraped, it looked like copper color underneath.

Could this be aluminum coated copper, tin coated or silver coated copper?

It doesn’t look like any of the wire at this site.

The wire appears to be original to the 1942 house. The covering is not plastic, it’s that older style, kinda cloth type insulation. My pictures probably don’t show it very well.

Can anyone help me with what this is? Is it a concern?




I have never seen or heard of any aluninum 12 or 10 that was anything but TW insulated in a plastic jacket. You are looking at tinned copper.

That was the conclusion that I was coming to, also. Thanks Greg.

This is back in Knob and Tube . It is tinned copper and the reason why the wire was tinned is because all joints where soldered back then an tinned wire was a lot easier to solder . The wire was rubber coated and cloth covered . Move it now and the insulation easily falls off.
Been there done that .
Roy sr

Thanks, Roy.

Alluminum Wire came into common use in the seventies.

Are there any issues using wire nuts to connect the old cable like this to new copper cable in Romex?

On a related note, how easy (or difficult) would it be for an electrician to pull out this old cloth coated wire, and feed in new conductors?

Tinned copper is still treated like coppere. You don’t have the aluminum issues

Not entirely accurate.

From this site (

“Aluminum wiring, used in some homes from the mid 1960’s to the early 1970’s, is a potential fire hazard. How safe is aluminum wiring? According to the U.S. Consumer Product Safety Commission, fires and even deaths have been reported to have been caused by this hazard. Problems due to expansion, or more likely micro-fretting and arcing at the connectors, can cause overheating at connections between the wire and devices (switches and outlets) or at splices. The connections can become hot enough to start a fire without ever tripping a circuit breaker!
CPSC research shows that "homes wired with aluminum wire manufactured before 1972 are 55 times more likely to have one or more connections reach “Fire Hazard Conditions” than are homes wired with copper. “Post 1972” aluminum wire is also a concern. Introduction of the aluminum wire “alloys” in 1972 time frame did not solve most of the connection failure problems. Aluminum wiring is still permitted and used for certain applications, including residential service entrance wiring and single-purpose higher amperage circuits such as 240V air conditioning or electric range circuits. The fire risk from single purpose circuits is much less than for branch circuits. But it’s not necessarily because of a “new alloy” as some folks assert. It’s because there are enormously fewer connections (four or six rather than 30 or 40 per circuit) and thus statistically a smaller chance of a connection failure. These connections do still burn up, as indicated by field reports.”

It is a concern near that time frame, but aluminum wire concerns go back to the 60’s…

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I just installed an Aprilaire 700 whole home humidifier and noticed silver wire was used on some of the parts. I am unsure if this is aluminum? The 120v transformer they supplied has both leads in silver wire, is this aluminum or tinned copper? My main concern is I’m using a wire nut to connect these leads to copper wire that I can then run to the control board in the furnace, so I don’t want to improperly connect aluminum and copper! Is it safe?

Tinned CU…based on the size of conductors you are likely dealing with it’s tinned. You can tell this by simply snipping off the end (very small piece) and looking at the end of the conductor. However, since it is new i am nearly 120% sure it’s tinned CU.

Or since you are connecting it to copper…just snip off the silver ends and strip off some new insulation and you will see that it is CU.

But I am assuming you did not read my more detailed response on 11/11/2016 at the link below…