Power/Ground wire Gauge?

[ChiTownLincoln 10+ year member]

I stopped at a car audio place last week and the tech showed me a 1/2" thick cable that he had running to the battery. Thats 1/2" metal not the whole thing. Today i was looking at wiring kits at the local auto parts place and 1 said "for 270w amps" and another said "for 2000w amps". The 270w package came with a 12 gauge power wire and the other came with something larger. I cant remember if it was 10 or 8.

Whats going on here? High voltage in our houses uses 12 gauge (from breaker to outlet). What's the point of using a larger gauge in a car? Is this a snake oil/myth that got out of hand?

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[vaiboy 10+ year member]

The problem is car audio amplifiers require high current(amperage) not voltage.

Voltage is the force that is pushing the electricity through the wire.

Amperage is a measure of the energy that passes a specific point in a period of time. Amperage is the gallons per minute of electricity.

Resistance opposes the flow of electricity, think of it like friction. When the current encounters resistance some of it's energy is converted to heat.

The conductor in wire has resistance, the smaller the diameter and longer the wire the greater the resistance.

Say you have a 1000 watt microwave in your home and a 1000 watt amplifier in your car. Just for the example we will say they are 100% efficient.

Voltage x Amperage = Wattage

Microwave

120VAC x amps = 1000

amps = 8.3

Amplifier

12.5VDC x amps =1000

amps = 80

As you can see the amplifier requires nearly ten times the current to produce the same wattage as the microwave. Resistance opposes current, if the resistance of the conductor is too high there will be excessive amounts of heat generated and voltage drop across the wire. Most household circuits are only rated for 15-20 amps so they can use higher resistance conductors than the power supply of a high current amplifier, but even household circuits have limits. You wouldn't run 12 gauge to 60 or 80 amp electric furnace that is a house fire waiting to happen.

 

[audioholic 5,000+ posts]

To sum up what vaiboy said, home wiring requires much smaller wire because it is 120 volts, as opposed to 12 volts in a car application. The lower the voltage of the system, the more "line loss" (voltage loss due to resistance in the wire) affects the final power available (volts * amps). Look at it like this, say your house wiring creates a 3 volt drop due to line loss. Now its only 117 volts, but that's only about a 3% loss. Now imagine that same wire size/length is used in a car application, and the same 3 volts is lost (resistance does not change). You now went from 12 volts, to 9 volts, a 25% reduction. This is an overly simplified description, but it usually gets the point across to the reader.

Its also worth mentioning that this voltage difference affecting line loss is also why its possible that we may have to run 0ga wire to the amplifier to supply it, but 12ga output wire can be used (speaker wire). The amplifier's output is significantly higher than the 12 volts of input supply so we can use much smaller wire for its output than its input. Remember, fundamentally an amplifier amplifies voltage. This is at the heart of what vaiboy was suggesting above.