Tinned copper
File or scrape a strand: copper shows under the tin. Heavy for its size, springs back when bent, solders easily. Often marked on the jacket of legitimate cable.
THE WIRE GUIDE — CHICAGO
Tinned Copper Wire: What It Is and Why It Looks Silver
Silver-looking strands that aren't aluminum: tinned copper is copper conductors coated in a thin layer of tin. Same copper underneath — the coating is there to fight corrosion.
THE CONFUSION
Silver strands, copper core — the visual test
Tinned copper is exactly what it sounds like: copper strands — usually stranded, sometimes solid — coated with a thin layer of tin, applied by hot-dipping or electroplating. The coating is microns thick. Underneath, it's the same copper as the bright stuff.
The confusion is understandable. You cut into a cable expecting copper and the strands come out silver-gray. Your first thought is aluminum — and if you haul it to the yard as aluminum, you'll get paid like it's aluminum. But tinned copper is heavier than aluminum, springs back when bent, and solders beautifully — three things aluminum won't do.
WHY TIN
What the tin coating actually does
Bare copper oxidizes. In dry indoor air that's a cosmetic patina; in salt air, damp bilges, chemical plants, and high-heat equipment, oxidation creeps into connections, raises resistance, and starts the slow failure that ends in a hot joint. Tin doesn't oxidize the same way — so a thin tin shell keeps the copper surface clean and conductive for decades.
That's why tinned copper shows up wherever corrosion is the enemy:
- Marine wiring — boat cable is tinned copper almost by definition; salt air eats bare copper.
- High-temperature and appliance wiring — tin holds up where bare copper would oxidize fast.
- Military, aerospace, and medical — spec'd wherever a connection absolutely cannot degrade.
- Bus bar and grounding — tinned copper bar and braid in panels and switchgear.
- Old cloth-insulated wire — some vintage conductors were tinned, which is another reason old silver-looking wire isn't automatically aluminum.
Tin also takes solder far better than oxidized copper, which is why tinned wire is standard in electronics and control panels — the joint wets out fast and stays clean.
IDENTIFICATION
How to tell tinned copper from aluminum (and CCA)
Three silver-looking conductors, three different metals. Here's how to sort them:
Aluminum
Silver-gray all the way through the strand — no copper anywhere. Noticeably lighter than copper, softer, doesn't spring back the same way. Jacket says AL.
Copper-clad aluminum
The sneaky one: a thin copper skin over an aluminum core. File a strand and you see silver-gray under the copper — the reverse of tinned copper. Jacket should say copper-clad or CU-CLAD.
The file-a-strand test is the whole identification kit. One scrape with a pocketknife tells you what's under the surface. Do not use a flame or lighter test — burning insulation gives off toxic fumes and tells you less than the file does. For the full breakdown, see copper vs. aluminum wiring: dangers, identification, and what to do about it — and if you're learning to read jacket markings, start with how to read the printing on electrical wire.
Got rolls of tinned copper — or any good copper wire — sitting around? It's still copper to us. We buy usable leftover wire — anywhere in the country. Fast, free quote.
FREQUENTLY ASKED QUESTIONS
Tinned copper questions, answered.
Why is my copper wire silver?
It's tinned copper — copper strands coated with a thin layer of tin to prevent corrosion. The tin looks silver-gray, but the conductor underneath is copper. File a strand to confirm: copper under the silver means tinned copper.
Is tinned copper wire worth anything?
Yes — it's copper. The tin coating is microns thick and doesn't change the metal value. What matters for value is whether the wire is usable (on the roll, intact jacket) or scrap, not whether it's tinned.
How can you tell tinned copper from aluminum wire?
File or scrape a strand. Tinned copper shows copper under the tin coating; aluminum is silver-gray all the way through. Tinned copper is also noticeably heavier than aluminum and springs back when bent.
What's the difference between tinned copper and copper-clad aluminum?
They're opposites. Tinned copper is a copper conductor with a thin tin coating (copper underneath). Copper-clad aluminum is an aluminum conductor with a thin copper skin (aluminum underneath). The file test tells them apart instantly.
Where is tinned copper wire used?
Marine wiring, high-temperature equipment, military and aerospace, medical devices, bus bar and grounding, and anywhere corrosion would attack bare copper. Some vintage cloth-insulated conductors were tinned too.
Can you solder tinned copper wire?
Easily — that's one of its advantages. The tin coating takes solder far better than oxidized bare copper, which is why tinned wire is standard in electronics and control panels.
Does tinning change the ampacity of the wire?
No. The tin layer is too thin to matter electrically — tinned copper is sized and rated exactly like bare copper of the same gauge.
IRONCREST KNOWS WIRE
I know wire. That's how I know what it's worth.
Reading a jacket is the first thing we do when a roll comes in — the letters tell us the type, the gauge, the rating, and whether it's resale inventory or scrap. That's also how we know when usable wire is worth more than the yard pays for it.