Does Ohms Law Apply Here???

Q: When building a true off-road rig, and not just a stock vehicle with a lift, it is usually nesssasary to re-wire some circuits to run the variouse accesories that you plan on using. Either way, you need to protect that circuit from an overload with either a fuse, fusable link, or a breaker. But how to you determine what rating of fuse to use? Would this idea work out okay: Measure the amount of resistance the load offers to the curciut Assuming the system operarates at 12 volts, use ohms law to figure how much amperage the load will draw given the voltage and resistance measurments

A: -When building a true off-road rig, and not just a stock vehicle with a lift, it is usually nesssasary to re-wire some circuits to run the variouse accesories that you plan on using. Either way, you need to protect that circuit from an overload with either a fuse, fusable link, or a breaker. But how to you determine what rating of fuse to use? Would this idea work out okay: Measure the amount of resistance the load offers to the curciut Assuming the system operarates at 12 volts, use ohms law to figure how much amperage the load will draw given the voltage and resistance measurments Then, pick the closest fuse. Use an amp meter in series with the load and fuse it over that by 20 to 50%. I.E. 10 amps of current use a 12 or 15 amp fuse. I have used a .1 or .2

ohm precision resistor in series with the load and measured the voltage drop across it, and then used ohms law to figure the current flowing in the circuit. A lot of things change resistance when the operating voltage is applied to them, (a bulb is one) so measuring it with an ohm meter will not give the actual value. -Resistance varies by its temperature so it's not possible to just measure the Ohms of a device to see what it will draw under load. Most items have a wattage or amperage rating, that's what I would use. W=EI or I=W/E. You need to go to a fuse rated probably 50-75% above the constant max load since many things draw more current when they first turn on