Electric cable
Electric cables, also called conductors, insulated conductors and wiring, are used for the transmission of electrical power, grounding and communications. For a Martian settlement the following requirements apply:
- It should be recyclable.
- It should be made in-situ from local resources.
- The insulation must be fire-proof if used inside a habitat.
Conductors
Most high voltage and high amperage conductors are aluminium, while copper is usually used in domestic distribution and communications. Both metals are recyclable. Conductors are temperature limited, and conductivity decreases with temperature. Although the embodied energy of aluminium is generally higher than for copper, the density of aluminium is 4 times lower, while the conductivity is about 2/3. So aluminium is less expensive to produce overall when evaluated in the terms of energy carried.
In a conductor, V=R*I where the voltage drop (V) is equal to the electrical resistance (R) * the current (I).
Power =Voltage * current, or W=V*I, or W=RI2, or W=V2/R.
Conductors are described by the American Wire gage system, from 24 to 0000, and then in the MCM (thouthands of circular mils) system from 250 to 2000. The system has many particular dimensions, such as 477 Aluminium wire, that is 477 MCM and used as its conductivity is equal to the older 300 MCM copper conductors it often replaces.
Most conductors inside buildings are likely to be sized following existing building codes, with a limitation in voltage drop of about 5%. So for a 480V system, motors will be rated to operate at 460V, and 120V at 115V.
Insulation
Glass fabric made from fiberglass is an interesting material for cable insulation, for it meets all above-mentioned requirements. See also lunarp:In Situ Electrical Insulation.
Plastics, such as PVC (polyvinyl chloride) could be manufactured on Mars from non edible biomass, that usually form at least 50% of vegetable production, of from hydrocarbons manufactured from CO2 and hydrogen using the Fischer Tropsch reaction.
Grounding
Grounding may pose a particular problem as Martian soil, being frozen, may not be very conductive. Extensive grounding may be required to complete electrical circuits and ensure that return voltages are not too high compared to various conductive elements in the settlement. Discharge of static electricity buildup in structural elements over poorly conducting ground will need to be included in electrical system designs.
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