[cyanb]

Question - has anyone had any luck getting 2 and/or 4ga cables through the firewall for audio installs?

Just curious as to how others have done it. After unstapling the carpet from the side moulding, it looks as though it's still in there pretty tight.. doesn't look as though it's going to be terribly easy to get cabling from the front to the rear of the car.

That having been said, I haven't found a good place to run a 4ga through from the engine bay into the car yet, and looking for ideas.

Anyone, anyone?

Thnx.

-Cyan

[DrPhyzx]

Originally Posted by cyanb

Question - has anyone had any luck getting 2 and/or 4ga cables through the firewall for audio installs?

My question is... why? The runs in a car are so short that impedance should not be an issue for smaller cables. 2 gauge cable is 0.5 ohms per KILOMETER. That simply doesn't buy you anything unless you are wiring a football stadium.

[cyanb]

I'm perfectly fine w/running a 4ga.. same problem. *where*

I've seen that the passenger side is a good place to go on the 04-07's .. was looking to see if anyone had done something similar on the 08s yet.

[DrPhyzx]

Originally Posted by cyanb

I'm perfectly fine w/running a 4ga.. same problem. *where*

I've seen that the passenger side is a good place to go on the 04-07's .. was looking to see if anyone had done something similar on the 08s yet.

4 gauge is 0.8 ohms/km. I was thinking more like 10 gauge, which will give you 0.01 ohms for a 10 foot run.

American wire gauge - Wikipedia, the free encyclopedia

[mattjk]

Originally Posted by DrPhyzx

4 gauge is 0.8 ohms/km. I was thinking more like 10 gauge, which will give you 0.01 ohms for a 10 foot run.

American wire gauge - Wikipedia, the free encyclopedia

those ratings are for 120v ac. as you go higher in voltage, less current is needed.

for a car, it is a different animal. where 10ga would be fine to run 120v, for over 300 feet (6amps for a typical 200w amp)

the same wire would only be good up to 7 feet at 30amps for a typical 200watt 12volt amp.

to go into the trunk, 8ga would be optimal for an amp with a 30amp load.

[DrPhyzx]

Originally Posted by mattjk

those ratings are for 120v ac. as you go higher in voltage, less current is needed.

for a car, it is a different animal. where 10ga would be fine to run 120v, for over 300 feet (6amps for a typical 200w amp)

the same wire would only be good up to 7 feet at 30amps for a typical 200watt 12volt amp.

to go into the trunk, 8ga would be optimal for an amp with a 30amp load.

What ratings? I'm pointing at the resistances per unit length of various wire gauges. I'm not sure what you think I was saying, but resistance is resistance, independent of voltage or current. Typical speaker loads are several ohms, so anything like 0.01 ohms is totally negligible.

[mattjk]

Originally Posted by DrPhyzx

What ratings? I'm pointing at the resistances per unit length of various wire gauges. I'm not sure what you think I was saying, but resistance is resistance, independent of voltage or current. Typical speaker loads are several ohms, so anything like 0.01 ohms is totally negligible.

what are you talking about? he's running a power wire, not speaker cables through the firewall.


ever try jumping a car with 10ga wire? starters take less than 15 amps and will cook a 10ga wire within 10 seconds.

[mattjk]

DC Wire Table

[DrPhyzx]

Originally Posted by mattjk

what are you talking about? he's running a power wire, not speaker cables through the firewall.


ever try jumping a car with 10ga wire? starters take less than 15 amps and will cook a 10ga wire within 10 seconds.

Sorry, I misunderstood the first sentence of his first post. Not enough sleep here to turn on my brain and wonder what he'd be doing with speakers under his hood

So... yes... the question is what is the power draw. Even for a big system shouldn't be more than a few amps, yes? Let's call it 10 amps... that would be about 0.1 W/ft ... should be no problem.

Lessee... 15 amp starter through 10 gauge should be 0.225 W/ft. Seriously, that's like 1/20th of a night light lightbulb per foot. That's not going to melt the wire.

===

I don't have any experience here so I did a quick search: a lot of amps at Crutchfield specify 30A fuses and call out 10 gauge wire for installation...

[DrPhyzx]

Originally Posted by mattjk

DC Wire Table

Yep... your table says 15A through 10 gauge is OK.

Now, 40 A in 10 Ga. would be 1.6 W/foot. That's almost half of a night-light bulb per foot, which sounds scary to me without some active cooling.

[mattjk]

Originally Posted by DrPhyzx

Yep... your table says 15A through 10 gauge is OK.

Now, 40 A in 10 Ga. would be 1.6 W/foot. That's almost half of a night-light bulb per foot, which sounds scary to me without some active cooling.

you're reading it wrong. the first section is AMPS, NOT GAUGE!

It says: 10ga wire, 30amps is goog only up to 6.6 feet.

[mattjk]

Originally Posted by DrPhyzx

Sorry, I misunderstood the first sentence of his first post. Not enough sleep here to turn on my brain and wonder what he'd be doing with speakers under his hood

So... yes... the question is what is the power draw. Even for a big system shouldn't be more than a few amps, yes? Let's call it sqrt(10) amps... that would be about 0.1 watts for a 10 foot length... should be no problem.

Lessee... 15 amp starter through 10 gauge should be 0.225 W/ft. Seriously, that's like 1/20th of a night light lightbulb per foot. That's not going to melt the wire.

no problem.

yes, it will melt. My coworker bought a jumper cable from the 99cents store. It was 10 gauge and it melted, no only the wire but damaged his bumper paint.

[DrPhyzx]

Originally Posted by mattjk

no problem.

yes, it will melt. My coworker bought a jumper cable from the 99cents store. It was 10 gauge and it melted, no only the wire but damaged his bumper paint.

Either the cable was defective (probable) or you were drawing more than 15A.

225 mW/foot is not going to melt.

[04STiguy79]

Run it through the firewall rubber grommet next to the drivers side floor board and run it along the trim panels along the floor back to the trunk, the easiest and cleanest way. Also remove the rear seat for easy access and for routing the power cable/RCA's/Ground.

[DrPhyzx]

Originally Posted by mattjk

you're reading it wrong. the first section is AMPS, NOT GAUGE!

It says: 10ga wire, 30amps is goog only up to 6.6 feet.

Sorry... not used to unlabeled table headings. Fact remains a lot of audio amps call out 10 gauge for 30A fuse (remember that fuse rating has a lot of headroom over nominal operation).

Please note that the point of that table is not safety issues from melting a wire, but not creating too much power loss (limited to 5%) for solar panels. This is not a solar installation, and that table isn't relevant to the discussion of overheating a wire.