Why Voltage Drop Matters in Automotive Wiring
Electrical accessories need adequate voltage at the load to operate properly. As current travels through a wire, the resistance of the conductor causes some voltage to be lost along the way. The amount of loss depends on factors such as wire size, conductor length, current draw, and conductor material.
Voltage drop can become especially important with higher-current accessories or longer wire runs. Lights, amplifiers, electric fans, pumps, inverters, winches, and other equipment may perform poorly if too much voltage is lost between the power source and the device.
Wire Length Can Make a Big Difference
A wire size that works well for a short run may produce considerably more voltage drop over a longer distance. This is why wire length should be considered along with current draw rather than choosing a wire gauge based only on the number of amps a device uses.
Remember that an electrical circuit needs a complete path. When entering a one-way distance in the calculator, the return path also has to be accounted for. This is particularly important when comparing different wire gauges for an accessory located far from the battery or other power source.
Planning a New Automotive Circuit
Before installing a new electrical accessory, determine its expected current draw and estimate the actual distance the wiring will travel. Routing around panels, through the engine compartment, or along the vehicle can make the real wire run longer than a simple straight-line measurement.
The voltage-drop calculation can then help compare different wire sizes and show how much voltage may reach the accessory. Wire gauge must still be suitable for the current and installation conditions, and the circuit should use appropriate protection, connections, terminals, and other components for the application.