Picking Power and Ground Cable Sizes
The following charts can give you some decent guidelines as to how big a cable you need to use for a particular power requirement. Originally meant for audio applications it has the same value for general automotive alternator and battery hookups. These figures have been rounded off for easy reference.
Ground cables should be the same size (or larger) as the power cable.
|Watts||Amps||4 feet||8 feet||12 feet||16 feet||20 feet|
** Current Draw figures are based on RMS Power of the amplifier with a 50% efficiency rating.
An amplifier rated at 100 watts RMS most often has a recommended power fuse rated at 20 amps at 12 volts.
Ohm’s Law says that P(power) = E(Voltage) x I(Current)
This suggest that this amplifier is capable of up to 240 watts maximum power at 12 volts. When a vehicle is running, voltage can be measured at 13 volts on average. Using Ohm’s Law again to calculate current draw for this amplifier at 13 volts at maximum current draw (fuse rating at 12 volts)
( P ÷ E = I ) or 240 ÷ 13 = 15.38 amps at maximum output. Our figure listed above for this 100 watts RMS rating is 16 amps.