A tin coating has been applied to copper for many years for corrosion prevention, especially in humid environments. It is still manufactured today for marine applications, but we only see tinned copper during home inspections of some mid-20th century homes at the larger gauge wires, such as service wires or to a range.
Because of the silver color, it is sometimes mislabeled by inspectors as aluminum. But it is easily differentiated by the older, cloth-embedded rubber insulation, and also by looking carefully at the cut end at a lug, where you can see the copper center, as shown below.
The tinned copper itself is fine, but the older-type rubber insulation that wraps it has lower heat resistance than newer wire insulation, and can crack and flake off as it ages. So tinned copper should be examined carefully for insulation deterioration.
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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 is a service conductor?
• 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 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?
• I heard that aluminum wiring is bad. How do you check for aluminum wiring?
• 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.