Voltage drop explains how the energy of a voltage source is decreased as electrical current flows through the passive elements (elements that do not supply voltage) of an electrical circuit. The issue becomes important when the length of wire becomes elongated. A common analogy used to explain voltage, current, and voltage drop is a garden hose. Voltage would be the water pressure supplied to the hose. Current would be the water flowing through the hose. And the inherent resistance of the hose is determined by the type and size of the hose, just like how type and size of an electrical wire determine its resistance.
Excessive voltage drop can cause loss of efficiency of light, motors, and appliances. This could result in lights that are dim with a decreased life expectancy for motors or appliances. To avoid excessive voltage drop, select a wire size that will minimize voltage drop. You need to know the length of the wire run and the amp load or current that will be on the circuit. To determine amps, add up the wattage of all electrical devices that will be on the circuit and divide that total by the voltage of the circuit, 110 or 220.
Here’s an example: let’s say you’re working with a 50-foot extension cord at 16 AWG trimming weeds in your backyard. Your voltage is at 125 and the current is 13 amps. Therefore, your voltage drop would be 5.22 volts or 4.18 %. Or, we can take a 100-foot extension cord at 16 AWG. The voltage drop for this extension cord is 10.44 volts or 8.35% as the total voltage.
In electronic design and power transmission, various techniques are employed to compensate for the effect of voltage drop on long circuits or where voltage levels must be accurately maintained. The simplest way to reduce voltage drop is to increase the diameter of the conductor between the source and the load, which lowers the overall resistance. There are also voltage drop calculators and wire size charts available on the web, in order to make things easier when weighing voltage drop for your particular application.