There's no single answer for how long a 12V cable can be; it depends on current draw (Amps), wire gauge (thickness), and acceptable voltage drop, but generally, longer runs or higher current needs thicker cables (e.g., 10 AWG for moderate loads, 2/0 AWG for high power) to prevent excessive voltage loss, with short runs (a few meters) allowing thinner wires like 24 AWG for very low loads (milliamps). Always double the one-way distance to get the total cable length and use a voltage drop calculator for precision.
Long lengths of wire have more resistance than short lengths. Thus, long lengths of wire will cause a larger voltage drop than shorter lengths.
As a general rule, a 12/2 wire with a load of 20 amps can be as long as 57 feet before it loses too much voltage to be effective.
But, to answer your question, yes, (electric) voltage does drop while traveling over long distances in/on wires.
voltage drop per 100 feet = 3/4 = . 75 volts per 100 feet. So, knowing that we can not allow anything greater than a voltage drop of .
When cable length is 50 feet or longer, voltage drop in cable occurs—the resistance in the copper measured per foot—causing heat buildup. With cord length beyond 50 feet, the heat buildup due to voltage drop can melt the cord and subsequently cause an electrical fire.
12 gauge- The minimum size for 30 amp use but not ideal. Best for shorter runs under 50 feet.
Use the Correct Wire Gauge: One of the most effective ways to prevent voltage drop is to use thicker wires. The thicker the wire, the less resistance it has, which means less voltage is lost along the way. For longer cable runs or higher current devices, always opt for a lower gauge (thicker) wire.
A 100 foot cord will have twice the resistance as a 50 foot cord. It is good practice to take into account the length of the extension cord by using the following table. This will result in a voltage drop of less than 5% due to resistance in the extension cord.
The NEC recommends a maximum of 3% voltage drop on feeders or branch circuits for branch-to-load, and 5% total (feeder + branch) for lighting and power at the furthest outlet. Utilities or manufacturers may impose stricter requirements.
From the diagram above the maximum length of the total wire back and forth should not exceed approximately 8 m for gauge #10 (5.26 mm2) . By increasing the size of the wire to gauge #2 (33.6 mm2) the maximum length is limited to approximately 32 m .
12-Gauge Extension Cords: Features and Applications
Even with equipment running 15 amps or more, a 12-gauge 15 amp extension cord guarantees consistent voltage throughout 50-100 feet, reducing the chance of overheating or performance problems.
12-gauge low-voltage wire: Ideal for long runs of 200ft and total wattage of up to 60W. 10-gauge low-voltage wire: Ideal for extremely long runs of 300ft and total wattage of up to 60W.
Long lengths of wire have more resistance than short lengths. Thus, long lengths of wire will cause a larger voltage drop than shorter lengths.
The maximum combined voltage drop on both installed feeder conductors and branch circuit conductors to the farthest connected load or outlet must not exceed five percent. This is the steady-state voltage drop under normal load conditions.
When a 208 or 240 feeder or circuit gets up to around 100' I do a voltage drop calculation. For 480 I generally do them when they get past about 250'. It's a really easy calculation to do so if I am questioning it at all I just do one.
The correct wire size for a 20 amp breaker is 12 AWG copper wire. It is rated 20 Amps at 75°C. Note that a 14 gauge wire on a 20 amp circuit is not the correct size, as it is only rated to handle up to 15 Amp in residential applications.
For a 12V system with a 100-amp load, cable size depends on distance. Use 4 AWG for short runs (up to 7 feet), 2 AWG for moderate distances (7-10 feet), and 1/0 gauge for longer distances (over 10 feet) or continuous high-draw applications.
Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage divided by resistance or the square of the current multiplied by the resistance) available from the source.
For residential applications, you must limit the voltage drop between the Point of Supply and the load to 5%. This means: The utility limits the voltage drop at the Point of Supply to 2%. As a guideline, you limit the voltage drop between the Point of Supply and the Main Switchboard to 2%.