Electrical Conductors

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Element Electrical resistivity @ 20°C Density (near r.t.)
Silver 15.87 nΩ·m 10.49  g·cm−3
Copper 16.78 nΩ·m 8.96 g·cm−3
Gold 22.14 nΩ·m 19.3  g·cm−3
Aluminum 26.50 nΩ·m 2.70 g·cm−3
Magnesium 43.9 nΩ·m 1.738 g·cm−3
Titanium 420.0 nΩ·m 4.506 g·cm−3
Lower number => better conductor r.t. = room temperature

Aluminum

Aluminum is commonly used as a conductor here on earth, in fact you use it every day without realizing it. High Tension cables have a steel core and an aluminum outer layer. It's used because losses are fairly low at 110kV and the weight of the cable and cost of the towers is important. Steel cored aluminum cable allows a longer span and is the most common form of aluminum wire used for HT lines on Earth.

Aluminum is abundant on the Moon.

One major disadvantage of Aluminum on Earth is that it corrodes rapidly in an oxygen atmosphere. The corrosion does not go right through however, only forming a thin layer on the surfaces exposed to oxygen. On the moon, in a vacuum environment, it would be an excellent material to use.

As a general purpose electrical conductor it's not great, but considering that copper is not readily available on the Moon there appears to be no choice but to use aluminum. This means regular supply voltages higher than 110V would probably be better. In some places on Earth it is illegal to use aluminum for general wiring mostly as a result of fire risk caused by contractors using too light a gauge in the past.

Copper

As a general conductor copper is the most commonly used on Earth because it's cheap, reasonably flexible, reasonably light and the 2nd best conductor and the best per unit weight. Copper allows for ease of soldered and crimped/clamped connections. It corrodes worse than silver, this is usually seen in older wires that have turned green.

Copper is not readily available on the Moon.

Gold

Gold is is not an especially good conductor at all, though it is better than aluminum but not per unit weight as gold is much heavier. It is very expensive, but compared to the cost of transport to the Moon from Earth, the cost is not significant. Gold is usually only used as a conductor in very specialized applications such as very fine wires like those used to wire bond integrated circuits to their lead frames.

A more important everyday use of Gold is in connectors

For connectors gold reigns supreme for several reasons

1. It doesn't tarnish (important on Earth, important indoors on Luna)
2. It's soft, so you can make the connectors tight and they dig into each other forming a good connection.

Gold is not readily available on the Moon.

Silver

Silver is the best known conductor, but in an oxygen rich environment it tarnishes. Silver is used in specialized equipment, such as satellites, and as a thin plating to mitigate skin effect losses at high frequencies.

In the Lunar outdoors, (in a vacuum where it can't tarnish), silver would be a marginally better, if heavier, conductor than copper, and a way better, but much heavier, conductor than aluminum.

Silver is not readily available on the Moon.

Magnesium

Magnesium is not an especially good conductor, being less conductive than aluminum but it is lighter. It has some other major drawbacks which make it completely unsuitable for use in electrical installations. Magnesium burns in oxygen, or nitrogen (forming magnesium nitride) or even carbon-dioxide (forming magnesium oxide and carbon). This means it's very difficult to extinguish. Magnesium also reacts with water.

Magnesium is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk.

Magnesium has many other uses but it is completely unsuitable for electrical wiring.

Magnesium is readily available on the Moon.

Titanium

External References

Electrical_conductor#Conductor_materials