LAYING CABLE

ELECTING the correct cable for your install is pretty important. The two main considerations are whether the cable is capable of holding the current you’re going to be sending down it and whether there will be an unacceptable amount of voltage drop along the cable length. To work out current capacity we have to go back to our Electrics 101 high school class and remember that the amps (current) is equal to the watts divided by the voltage. Say you have a 50W light you want to power, we know the voltage is 12V (actually it’s 13.8ish when your car is running, but let’s not get bogged down with details) so 50/12 gives us a figure of 4.17amp. It’s not a great idea to have a cable that’s operating at the upper end of its capacity, so you’d use wiring that’s rated to 10amp or above in this instance. However, cable does introduce resistance to the current, and the longer the cable is, the greater the resistance. There is a mathematical formula to work out resistance over cable length, but frankly it’s probably unnecessarily complicated and involves determining the cable’s resistance per metre (in ohms) so we won’t bore you with the brainsplosion. If you really care, there are plenty of voltage drop calculators online, or you can just use the rule of thumb: if you’re unsure if the wire is suited to the task, go up a size. Because, science.