Copper is used for electrical wires because it has high electrical conductivity (which is another way of saying it has low resistance to the flow of electrons), enough tensile strength, enough ductility and is not normally brittle.

If copper is beaten into a thin sheet or drawn into a fine wire it becomes brittle (called "work hardening") but it can be made soft again by heating it enough, i.e not up to its melting point, and then allowing it to cool slowly.

Other materials with higher conductivity are either too expensive (like gold) or too brittle to be good candidates for use for electrical wires.

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Copper is used because it is a good conductor of electricity. The conductivity of silver is greater than copper but we use copper because copper is cheaper than silver.

Copper combines several properties that have traditionally made it preferred for most electrical wiring. Copper is a good electrical conductor, provides a good contact surface, is ductile (is easily bent repeatedly without breaking) and it is not too expensive. Copper wire is also relatively easy to manufacture, and there is a long history of using it.

However, other materials can and are used for electrical wiring. Furthermore, in the future it is reasonable to expect that copper will fall out of favor as new and better means of conducting electricity are better developed and perfected.

Aluminum wires conduct electricity with about 1/2 the weight of copper for a given amount of electricity. It is also less expensive than copper. The problem with aluminum is that the surface of the wire oxidizes, forming a non-conductive layer. Unless cleaned-off thoroughly before making wire connections, oxidation makes a joint have high-resistance, which, at high current flows, causes overheating which can start a fire.

After making a connection the aluminum joint must be protected from the air to prevent further oxidation from taking place. Because of the need to take care making connections which do not have high resistance and the need to take the proper steps to prevent further oxidation, using aluminum wire is much more expensive than using copper wire except for very long runs.

The ends of aluminum wire can be terminated with short lengths of copper for connection but this adds cost and complexity. Although properly-made copper-coated aluminum is less expensive, lighter and just as safe as copper, it is not used very much.

"Nanowire" made of carbon nanotubes can be used to conduct electricity at 1/6 the weight of normal copper. The main problem with using nanowires has been that they are extremely expensive and very short. An economical means of connecting short lengths of nanotubules to produce a practical wire has not been demonstrated yet.

Another electrical wire based on the metals sodium and lithium has recently been patented and is expected to be available in a few months. For the same amount of current flow - depending on whether the electricity to be conducted is constant or impulsive - it conducts electricity at about 1/3 to 1/1000th the weight of copper.

Lastly, there are a variety of superconducting materials. However, they require cooling with liquid nitrogen or other very cold liquids. The physical size of the cooling equipment - and its high cost - makes the use of superconductors impractical and uneconomic for most ordinary applications, so they are used only for major scientific and industrial projects.

Copper is sometimes nickel-plated to prevent oxidation in high temperature environments.

Often copper electrical terminals are gold-plated to help to prevent surface oxidation.

If wire used to carry high frequency currents - such as for radio, television and local area networks - its cross-sectional area is usually like tubing that is silver plated. This works fine because only the wire's surface "skin" actually carries most of the current at high frequencies.

The big wires on national grid transmission lines are usually made of aluminum sheathed steel cable. The physical "skin effect" of the flow of current through wires means that most of the current is carried in the aluminum which is the outer 1/8" or so. Also aluminum weighs a lot less than copper or steel. The steel cable core can handle 200,000 psi so you can put the supporting towers much further apart than if only pure copper or aluminum were used.

The twin-lead telephone wire drop into your house is probably made of copper plated steel wire.

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Copper is used because it is a good conductor. It's a good conductor because it has lots of free electrons.