Power/Current Draw and wire thickness

[RSDXzec 10+ year member]

I currently have 8awg power wire to my amp and I was told by a few on here that after 500watts I should upgrade to a higher thickness.

What I don't understand is: if P=I^2*R then I=sqrt(P/R)

So on a 4 ohm load I could still use this wire for a much higher power draw than on a 1 ohm load. As I understand it, cables are rated for certain currents, not power draw as the current drawn changes at different impedances.

My fuse is 60Amps on this wire and my plan is to push 500Watts to a 1.34 ohm load.

Using the equation above and using 80% amp efficiency give me 24Amps (my amp is rated at 85% efficiency), even pushing 1000watts I would only be at 34Amps draw.

After taking into account box rise the draw would further decrease as the denominator (impedance) would increase.

So is there any reason other than the slight increase in Vdrop that would result in needing a thicker wire? Because it certainly can take it.

My other question is am I better off buying a second 8awg cable or replacing it with a 4awg wire? which could take more current?

Cheers.

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[goingdef 10+ year member]

google wire gauge amperage chart, it will tell you how many amps compared to the length of the wire, it will also tell you how high of a fuse you can safely run on your amps power wire to lower current resistance, fuse for the max allowance of the wire not the amp.

 

[JoeK 10+ year member]

4AWG is so cheap that you should just do it anyways. Its like $1/ft; i wired my whole car up on about $25 of 4AWG soundquest wire

 

[RSDXzec 10+ year member]

4AWG is so cheap that you should just do it anyways. Its like $1/ft; i wired my whole car up on about $25 of 4AWG soundquest wire

here in aus 2g wire is $15 per metre, so i'm guessing 4g is around the $10 mark.

google wire gauge amperage chart, it will tell you how many amps compared to the length of the wire, it will also tell you how high of a fuse you can safely run on your amps power wire to lower current resistance, fuse for the max allowance of the wire not the amp.

yes but my question was that the amount a wire can carry is measured in amps, so why do people here say over x amount of watts you need x size wire, when really it depends a lot on the impedance of the system in question. I mean the way I've calculated it I could run 1000wrms on 8g wire...

 

[goingdef 10+ year member]

here in aus 2g wire is $15 per metre, so i'm guessing 4g is around the $10 mark.


yes but my question was that the amount a wire can carry is measured in amps, so why do people here say over x amount of watts you need x size wire, when really it depends a lot on the impedance of the system in question. I mean the way I've calculated it I could run 1000wrms on 8g wire...

you could on a couple feet of it, but a 1000w amp is generally fused for 100 amps or better if it's under rated and I would not try/trust to run that on a 13-16 foot run of what I trust for sub speaker wire!

also it's all about fighting impedance in the wire!

 

[maylar 10+ year member]

For typical systems with typical efficiency 8 gage is fine for 5-600 watts. With efficient Class D amps you can stretch that to 750 watts.

Every 3 wire gages is twice / half the circular mils.. which means 2 x 8 gage wires is equivalent to a 5 gage. A single 4 gage is bigger.