Definition
Copper electrical wire whose individual strands have been coated with a thin layer of tin (or tin-lead solder) before the strands are bundled together. The tin coating prevents the copper from oxidizing, keeps the strands from corroding in service, and makes the wire much easier to solder cleanly.
Plain English
A copper wire whose strands have been given a thin silvery coating to stop them rusting and to make them easier to join with solder.
Context Anchor
Seen in aircraft electrical maintenance, especially when inspecting or replacing wiring in areas exposed to moisture or corrosion.
Derivation
From 'tin,' the soft silvery metal long used as a protective coating on other metals. To 'tin' a wire means to apply a thin film of tin to its surface. The term is descriptive: the wire has been tinned.
Why Pilots Care
The tin coating prevents corrosion that could cause electrical failures or intermittent connections critical to flight safety.
Intuition Check
Do not read “tinned” as meaning “put in a can” or “made of tin.” Here it means copper wire with a thin tin coating.
Example Sentence 1
The mechanic used tinned wire when rewiring the navigation light circuit so the connections would resist corrosion in the wing.
Example Sentence 2
During the annual inspection the mechanic noted that all new wiring runs used tinned wire as specified in the maintenance manual.