How to select the CORRECT wire size

Standard

CABLE SELECTION BASED ON POWER NEEDS

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.


Recommended Cable Size by Power and Length
Total Power
(watts)
Cable Length
4 feet 8 feet 12 feet 16 feet 20 feet
100 10 10 8 8 4
200 10 8 8 4 4
400 8 8 4 4 4
600 8 4 4 4 4
800 4 4 4 2 2
1000 4 4 2 2 2
1400 4 2 2 2 2

 

Current Draw by Power
Total Power Current
Watts Amps
100 16
200 32
400 64
600 96
800 128
1000 160
1200 172
1400 188
** Current Draw figures are based on RMS Power of the amplifier with a 50% efficiency rating.

 

Cable Specs
Cable Size

(gauge)
Current Capacity

(amps)
1/0 350
2 225
4 150
8 100
10 60
12 40
14 25
16 15

Example

An amplifier rated at 100 watts RMS most often has a recommended power fuse rated at 20 amps at 12 volts. Since 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 ) 240 ÷ 13 = 15.38 amps at maximum output. Our figure listed above for this 100 watts RMS rating is 16 amps.

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