Electricals & Electronics

Is It Aluminum Wiring or Tin-Clad Copper Wiring?

Solid strand aluminum wiring that was used for 15 and 20 amp circuits (receptacles and lights mostly) in older homes (not newer multiple strand for 30-40 amp dryer or range) has earned itself a bad reputation and justifiable so. Here is some comparison with its copper counterpart and why aluminum quickly became unpopular.

Aluminum Electric Circuit Wiring Characteristics

  • Less ductile: Simply put, aluminum can only withstand so much bending, twisting, clamping etc. before it fails not necessary externally but also internally which reduces it s ability to carry current significantly, leading to a buildup of excessive heat due.
  • Higher electrical resistance: Less current carry capacity simply means you need a bigger wire than would be required by copper conductors.

  • Galvanic Reaction: Aluminum is selectively compatible with other metals causing a reaction that leaves deposits and compromises solid  connections to fixtures. Loose connections and electricity do not go hand in hand. It is a recipe for overheating, arcs and possibly fires.
  • Greater malleability: Aluminum is sensitive to compression. After a lug has been over-tightened on aluminum wiring, the wire will continue to deform or “flow” even after the tightening has ceased. This deformation will create loose connections, increases electrical resistance, heat build up, arcs which could be fire hazards.
  • Expands and contracts with higher temperature: Aluminum expands and contracts with changes in temperature more than copper. As you may already know or guessed correctly, loose connections and the rest of the problems with loose connection exists.

While aluminum can be made safe (there are electricians who specialize in this), the cost of doing so or replacing the wiring makes being able to spot the presence of aluminum wiring a must-have skill set when hunting for a new home or property.

Basics of identifying aluminum wiring

  • The wire is silver colored. Going by this indication alone is merely a
  • n indication and is probably only 60% accurate. A silver coloured wire should make you go into aluminum alert mode.
  • Look for the word “aluminum” or the initials “AL” on the wire jacket where visible such as around the electric panel, unfinished basement ceilings or if possible and safe, the attic.

Hopefully this helps you hone your aluminum identification skills next time you’re home-hunting.

Aluminum Wiring with Marking


Well that is not all, there are plated or tin clad aluminum that could throw you off. Just as important as it is learning to identify AL, it is also important to learn what is NOT AL because not all wires that are silver coloured is Aluminum.


Tin Clad Aluminum
Tinned copper conductors in electrical wiring was introduced to comb

at oxidation and damage to copper conductors when they were insulated using a rubber sheath – a condition noted in the U.S. by the mid 1920s. The Sulphur content in rubber insulation on wires interacted with the surface of the copper wire, damaging the conductors. A thin coating of tin on the surface of the copper conductor was applied to both solid conductors and multi-strand conductors to protect the copper conductor from damage.
Tin clad copper looks like aluminum but is actually copper.

Walking away from a home or property purchase simply because tin clad copper was misidentified as aluminum would probably hurt.

  • Basics of Identifying tin clad aluminum
    As with electrical wires generally, a reliable way is to look for markings on the wire jacket where visible that suggests the wire is actually not aluminum. You might see copper or CU on the sheathing somewhere around the electric panel, unfinished basement ceilings or if possible or safe, the attic.
  • Nicking or scratching the suspected aluminum wire on the exterior tin coat would reveal a red copper wire colour behind. Warning! Toying with electricity and live circuits risks electrocution. Be guided! Make sure circuits are de-energized before attempting this except you are trained and confident.
  • Plated copper wire [tinned copper wire] is relatively common in older homes, and it looks like aluminum wire. It was commonly used with rubber-based insulation. Identification can be made by careful inspection of a cut end of the wire because the square-cut end of the wire or a splice reveals a red copper wire core (middle portion). This is mostly visible at the neutral wire connection bus.

Watch out: tin-plated copper wire is a completely different product

that, because its conductors sport a thin plated silver colored surface, might be mistaken for unsafe aluminum wire. It is not aluminum and it is safe unless, as with any electrical wiring, it has been damaged in some manner.

Hopefully this article helps you and your clients identify aluminum wire easily or at least know when to request professional help or assistance. If you suspect that a prospective property has aluminum wiring, have your Home Inspector verify its presence during the Home Inspection and discuss recommended next steps.

Our InterNACHI, CAHPI, Mold, Radon Certified Inspector & Indoor Air Consultant can always to help you.


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