No, we have never seen any aluminum wire in pre-1960 homes. Although it has been used since the early twentieth century by utility companies for electrical transmission in high-voltage power grids, copper wire has long been the standard for residential wiring. Solid aluminum (not multiple strand) wire was used only briefly for general home wiring, from 1965 to the mid-1970s, as a copper alternative during a period when copper prices skyrocketed. 

    An example is shown above. But the large number of house fires, caused by connections of single-strand wires working loose at wire terminal connections, ended the the era of single-strand aluminum home wiring.

  Although single-strand aluminum wiring is gone, multi-strand aluminum wire is still an approved residential wiring and we see it used regularly for the main service wires from the outside weatherhead to the panel and also at breakers for major appliances. Because it is required to be coated with anti-oxidant paste at the wire connections where the metal is exposed to the air, sometimes the only way we know that it’s aluminum wire is the presence of the black or gray anti-oxidant goo, like in the photo below.

   If you peek inside the electric panel in a pre-1960 home—which, by the way, we do not recommend unless you are looking over the shoulder of a home inspector or professional electrician—it may appear that some of the larger, multi-strand wires are aluminum, based on the silver color of the wire strands, like the two wires connected to the lugs in the photo below.

   But these wires are actually tin-coated copper, which was used up until the mid-1950s or so. If the insulation is rubber with an embedded cloth sheathing, the wires are definitely tinned copper and, if you look closely at the exposed metal at the connection to the lug or circuit breaker, you can usually see little gleaming flecks of copper color where the wire has been nicked when the insulation was stripped back. 

    Also, see our blog post I heard that aluminum wiring is bad. How do you check for aluminum wiring?

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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:

• Which house appliances need a dedicated electrical circuit?

• Can a short circuit cause a high electric bill?

• What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?

• Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?

• What causes copper wires to turn green or black in an electric panel?  

• What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?

• Why is it unsafe to bond neutral and ground wiring at subpanels?

• Should I get a lightning rod system to protect my house?

• Why is a strain relief clamp necessary for the cord connection to some electric appliances?  

• Does a wire nut connection need to be wrapped with electrical tape?

• What is the minimum clearance of overhead electric service drop wires above a house roof?

• What are the requirements for NM-cables entering an electric panel box? 

• What is the color code for NM cable (Romex®) sheathing?

• Why is undersize electric wiring in a house dangerous? 

• What causes flickering or blinking lights in a house?

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• How can I find out the size of the electric service to a house?

• Can old electrical wiring go bad inside a wall? 

• What is an open electrical splice?

• What are the most common electrical defects found in a home inspection? 

• What is the life expectancy of electrical wiring in a house? 

• What is an "open junction box"? 

• How dangerous is old electrical wiring? 

• What is a ground wire? 

• What is "knob and tube" wiring?  

• What is the code requirement for receptacle outlets in a closet?

   Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.