Sizing Electrical Cables
There are two main problems when it comes to transmitting electrical energy though wiring. The first is the resistance of the wire, which is a factor determined by the material, its purity and surrounding magnetic impedance factors.
The second problem is the heat generated when the electricity encounters resistance. An extreme example of this would be to to run the entire power supply of one’s home though a small copper wire, like the kind used in headphones, which of course is far too dangerous to actually do.
The result would be the wire turning white hot almost instantly before either vaporizing or melting into a molten puddle. By contrast, if a technician were to try to run a simple low voltage audio signal though a huge steel bar line, it would degrade beyond audibility quite quickly due to resistance.
Choosing the Wire Gauge
There are two main factors to consider when choosing a wire gauge. The first factor is what gauge is required by local fire, building and electrical codes to be legally used. The second factor is whether or not any other gauge of wire is acceptable for the job by using a different approach.
For example, it may not be legal or safe to use a lower gauge wire to transfer a high wattage between two points, but if the starting end of a circuit splits the current evenly between several lengths of a lower gauge wire the wattage is reduced per wire. The transmission wires can the be recombined at the other end of the circuit to achieve the initial level of energy concentration.
When in doubt, refer to the local electrical code or defer to an electrician for advice.