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What is tinned copper wire?

Why copper wire looks grey

In this article we'll discuss the concept of tin-coated copper wire.

Copper is a great conductor of electricity. But it's also highly prone to corroding unless it's protected with a non-corrosive coating. That's where tin comes into play, and why oxygen-free copper wire often looks silvery-gray. Read on for the details.

A tinned wire and an untinned wire

Crutchfield tinned ground and untinned positive 1/0-gauge power wire

What is "tinning" and why do they do it?

Tinning prevents rust and, when applied to the ends of twisted wire, keeps the strands neatly together for clean and reliable connections with no loose, stray wires that could cause a short circuit. Tin and lead-zinc solder are common materials used for protective coating because they don't rust or react adversely with the environment.

Almost all wire manufacturers tin their oxygen-free copper wire for protection. Even the individual strands in stranded wire get coated. The tinning process makes copper wire look silvery-gray. You can scrape off the coating with a knife, if you want, and see the copper-colored conductor in tinned copper wire.

A tinned wire end, with the tin scraped off, exposing the copper underneath

A tinned wire end, with the tin scraped off, exposing the copper underneath

Wire construction

Wire is made by pulling a conductive metal through smaller and smaller circular machine dies until the resulting thin cylinder is the right size in diameter. Then the wire is given a thin protective coating by electrolysis or by being dipped in a molten coating material, like tin, solder, or in some cases clear plastic or enamel. Finally, the wire gets coated in a thicker insulation material, like PVC or nylon.

Several cube blocks of metal, with a copper block in the center

Metal conductors

Wire can be made from almost any conductive metal. Silver is the best, but is expensive (about $700 a kilo, as of Feb. 2022) and readily tarnishes, oxidizes, when exposed to air, losing its conductivity. Copper is the second-best conductor of electricity, cheap (around $2 a kilo), but also oxidizes in air. At number 3, gold will never tarnish or rust, but is very expensive (about $58,000 a kilo), so it's used only for coating contacts and terminals. Aluminum is next, is cheap (about $3 a kilo), and is used in a lot of different kinds of electrical installations. Aluminum wire also oxidizes and loses conductivity without a protective coating.

Aluminum wire

More importantly, aluminum wiring cannot carry as much current as an equivalent-sized copper wire, and so is limited in capacity. Also, aluminum wiring doesn’t work well with copper, brass, or steel terminals and fittings, causing undesirable conduction and heat issues. Over-loading aluminum wiring is a common and dangerous problem in the housing and mobile electronics industries. Copper-clad aluminum (CCA) is used for improved conduction and weight as well as cost reduction in many applications, but should not be depended on to deliver as much power as a pure copper wire would.

The colors of corrosion

Another incipient quality of aluminum is that when it corrodes to aluminum oxide, it doesn't change color — like iron oxide is red, copper oxide green, and silver oxide black — but just gets scaly and dull, so you might not notice when an aluminum wire's been compromised.

King copper with a tin crown

Copper wins, because of conductivity and cost. And because oxygen is the cause of corrosion, manufacturers super-heat their copper to burn away any air before encasing it in protective tin coating and insulation. That's why we like tinned 100% oxygen-free copper wire the best for all our wiring.

two tinned copper wires

Protect the connections — leave the tinning intact

The enemy of a good connection is corrosion, so anything that keeps water and oxygen away will help protect it. Corrosion in a power wire connection will increase resistance to the current flow and possibly get hot enough to melt wires and plastic fittings.

Exposed copper will rot

You would think that the absolute best way to make a connection, with the best conduction and least resistance, would be to scrape off any coating and make bare copper touch bare copper, tighten the conductors together, and then cover everything with a protective coating like tape, paint, or non-conductive electrician's grease.

But this doesn't always work in salt spray environments. In fact, doing so often accelerates the onslaught of corrosion by galvanic (electric) activity throughout the connection and the protective coating due to the contact between salt water and the different metals. A car environment can often be just as challenging as a marine one, so the same preventative measures will apply.

Tinning is your friend

Seeing as most wires and wire terminals, especially marine-grade wires and fittings, are already tin-coated, the best way to make safe and long-lasting connections is to leave the coatings intact, and, at most, give the finished tight connections a thin coat of solder.

tinned ring connector crimped to a tinned wire, showing a good connection with the tinning intact

Best practice is to leave protective coatings intact

Good connections

After crimping a ring connector, spade connector, or wire ferrule onto a wire end, a good practice is to then solder the parts together for strength and protection. A light coating will do best — using too much solder will compromise the conductivity and strength of the connection. Solder is a protective coating and an adhesive — it does not improve electrical conduction or current flow.

We only carry the best wire

All the wire Crutchfield sells is made of copper — not gold, silver, or unicorn bones. Most copper wires are tinned. Even the wires inside jacketed RCA cables are often tinned for protection against oxidation from contact with the air. It's true that some of our more expensive home theater speaker cables don't have tinned copper conductors, but they do sport elaborate air-proof insulation and shielding, plus gold- or silver-plated connectors to prevent corrosion instead.

Different wires for different functions

Crutchfield carries a few different high-quality brands of wire for almost all occasions. Check them out from the links below.

Call us for your wiring needs

If you have any questions about wiring or need help choosing the best wire for your job, give us a call to contact our advisors. And be assured that when you buy your wire from Crutchfield, you'll get access to our legendary free tech support to help you install and enjoy your sound system.

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