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I am running 4awg wire to my car's 400watt amplifier. The wire is running about 10 feet from the circuit breaker that it is connected to. The circuit breaker (as of now) is connected to the car's battery via about 18 inches of 6awg wire.

Should I be worried about using 6awg wire between the battery and the breaker - or since it's so short will it be ok? All of the wire I'm using is pure copper welding cable from TEMCo, not the aluminum stuff you get in Amazon and eBay kits. That gives me peace of mind but I want to make sure that this is not a bad way to set up the system.

I know that the amp is only going to use about 33amps at max, but I want to be sure that it won't cause any problem in the long run... (Pun intended)

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2 Answers 2

up vote 3 down vote accepted

According to this chart. 8 gauge is sufficient for 400watts rms for 8 feet. so 6 gauge should be perfectly fine.

If you want to be extra sure then you should do a voltage drop test.

Start and run the vehicle playing music at the max you would listen to it. Measure the voltage across the battery terminals and record the reading. While keeping the negative lead still attached to the negative of the battery measure the voltage at the positive terminal of the amplifier. Record the reading.

Subtract the second reading from the first reading to get the voltage drop. If the drop is significant. eg. 14.3v at battery. 13v at amp then you might want to upsize the cable. If it is more like 14.3v at battery 14v at amp I wouldn't worry about it.

Basically you don't want the amp to see less than 11.2v approximately. A very low battery level would be 11.8v so a .6v drop is probably pushing it. .3v drop is probably safe though.

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Thanks for the technique. I'll give that a try in the morning. –  Sponge Bob Jul 11 '13 at 6:30

18 inches doesn't seem like enough length to be too concerned. Most sources back up your assumption that 12 volts x 33 amps isn't a problem for 6 awg wire at only 1 or 2 feet. The charts below suggest you would only run into problems past 10 feet at 6 awg.

Keep in mind though, electricity can be unforgiving. Insufficient wire could have dangerous and deadly consequences if you get it hot enough to cause a fire. So, just be careful out there.

http://www.allfordmustangs.com/forums/attachments/audio-alarms/62425d1235669252-wire-gauge-ampacity-table-wiringdiagram.jpg

http://docs.engineeringtoolbox.com/documents/730/12V_cable_maximum_amps.png

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