In its most basic form, 12 volts are equivalent to 12 units of labor. If your line has a 2% voltage drop, it is using 0.24 volts, or units of labor. That leaves 11.76 volts (or units of labor) available. So, a line marked "12-volts" uses about 1 unit of labor.
The voltage of a wire is the force per unit length between the wires. The more force per unit length, the higher the voltage. For example, an electric fence can be as high as 600 volts while a household circuit is only 120 volts. A metal object will prevent electrons from moving through it so there is no current flow but the wire still creates a voltage because it is a continuous loop so there is no path for electrons to take.
Electricity is the flow of electrons through a conductor such as a copper wire. The amount of electricity that flows is called current. Electric circuits always include at least two elements connected together: a +ve terminal or pin and a -ve terminal or pin. These terminals are called buses because they carry current freely from one element to the next. Buses may have other names depending on what kind of bus they are; for example, a ground bus is a common reference point for removing electrical noise from a system.
Current flows from the positive terminal toward the negative terminal across any conductor which connects them.
Of course, with a low-voltage system, safety is paramount, but power loss is what drives cable size the most. A 10% power loss in a 12 volt wire is 1.2 volts! Some gadgets may be rendered inoperable as a result of this. For example, some digital cameras need about 12 volts to work properly, so if there's a short circuit anywhere in the cable run, they will shut down immediately.
The best way to avoid power losses is to use 14 gauge or larger wire for all circuits. This will provide the maximum possible current capacity, which reduces the risk of fire. However, if you only have access to smaller wires, such as #14 copper tubing, you can still reduce the risk of fire by enclosing each circuit in an independent metal conduit. Make sure that you use heat-resistant tape to cover the ends of the conduit when attaching it to other structures or equipment.
The amount of power lost in a wire depends on its diameter. The thicker the better, up to a point. Thicker wire requires more force to break, which means less chance of damage from accidental contact. Also, thinner wire is more likely to get damaged over time from exposure to moisture or corrosion. Finally, if you're trying to keep weight down, then thin wire is not as efficient as thick wire at transferring power from battery to load.
Losing a single volt of electricity in the wire represents a massive 8% loss in automotive applications of just 12V, so it may be a huge concern for voltage-critical applications like your headlights, where higher voltage means more light. A human hair is about 40 microns wide and lies approximately 2.5 million miles on the earth's surface. So at a rate of one mile per hour, you would need about three hours to cover a quarter of a mile with a string of lights powered by a voltage divider.
In practice, the actual loss will be less than this because some of the power is lost as heat within the conductor, but eight hundred watts is a lot of heat to put out into the atmosphere every minute!
The other major source of loss is radiation from the conductor itself. The most effective way of reducing the risk of cancer from electrical radiation is to avoid exposure altogether or to limit exposure as much as possible. But even if this wasn't the case, many experts believe that the benefits of lighting our lives with electricity outweigh the risks. For example, it is estimated that if all US electricity were generated using nuclear power, the average person would get an extra 1 year of life thanks to reduced stress levels from not having to worry about pollution or global warming.
The amount of power lost to radiation increases with the fourth power of the conductor's diameter.
In 12Volt systems, we try to stay on the safe side of Australian Standards, which state that we should have less than 5% volt-drop. That is 0.6 volts or less for 12-volt systems. In other circumstances, the calculator may provide us with one cable size that is exactly 0.6 volt drop and another that is less, say 0.4 volts. We would want the lesser voltage because it provides more room for error if we need to make adjustments to the wiring later on.
The voltage drop across any wire will reduce the total voltage available to our circuit, just as if someone took away part of its power supply. So, if we have 10 volts coming in from a power source and there is a 6-volt drop across a cable, then 8 volts will remain after the cable has taken its loss.
Now, if we need to send signals over long distances, we will need different cables. Cables used for sending data signals need to have less voltage drop for them to be readable at the receiving end. In most cases, this means that we will need two types of cables: one with a small voltage drop for use within our office or home network and one with a larger voltage drop for use between buildings or with other circuits outside our immediate area.
For example, let's say we want to run a cable from our desk to the wall socket and connect it up so that we can transmit data over the line.
The voltage is normally dictated by the system (battery or generator) and remains constant if the system is functioning properly (until voltage drop from resistance occurs, which is a whole 'nother bag of worms). So, according to Ohm's Law, 12 volts at 10 amps produces the same amount of power as 120 volts at 1 amp = 120 Watts.
However, power is power, no matter what level it is being used at. If more efficient motors become available that can run on 12 volts but not on 120 volts, then these motors would be able to use less energy per unit time than older motors that need higher voltages to operate them. This would lead to a reduction in the overall cost of operation for the motor, because fewer batteries are required to do the same job. Modern motors tend to be quite efficient, so this isn't an issue anymore. A common example of this is when a car owner uses 24 volts instead of 120 volts to power their car's door locks, this saves energy since the total voltage needed from the battery is reduced by one third. Door lock systems now exist that can operate correctly using 12 volts even though most other components of the car require 120 volts to function.
In conclusion, power is power, no matter what level it is being used at. More efficient motors are available today that can run on lower voltages, so this is done to save energy.
Depending on the current load and length of the circuit, household wiring for 120-V circuits is nearly usually 12- or 14-gauge copper wire. A 12-gauge copper wire has a metal conductor diameter of 0.0808 inches, whereas a 14-gauge wire has a diameter of 0.0641 inches.
The general rule is that you should use wire no smaller than what the circuit will bear without breaking down. For example, if you're sure your circuit will never carry more than 15 amps, use 15-amp wires. If in doubt, use 16-amp wires because they're almost always available where 120-volt power is used.
Household wiring for 240-V circuits is usually either 2 or 3 wire. 2-wire branch circuits can handle up to 20 amps while 3-wire branch circuits can handle up to 30 amps. The voltage between any 2 points on a 2-wire branch circuit cannot exceed 15 volts maximum. The voltage between any 2 points on a 3-wire branch circuit cannot exceed 20 volts maximum.
Because electricity always takes the path of least resistance, it's important to ensure that all branches of 240-volt circuits are crossed with solid conductors. Otherwise, you might get a short circuit when something breaks or an open circuit when something burns out.
Household wiring for 400-V circuits is usually 4 wire.