I recently had two amps installed at Quality Auto Sound. An old one just went out, so I bought a Phoenix Gold Xenon x100.4 to go along with my MTX 500D for my Sub. The MTX is rated at 250rms, but actually probably runs closer to 450rms. They installed a 60A fuse by the battery for the 4ga wire, and back in the trunk is a distribution block with 2 60A fuses splitting the wire into 2 8ga lines into the amp's. The xenon amp says it requires an external 80A fuse. The MTX has 3-25ga fuses in it. My question is, Should the fuse by the battery be bigger? From reading around sounds like I should go with a 125A, or add the fuse requirements on the amps, which gives me 155 and go with something in that range, or does that have nothing to do with it. Then I beleive I should probably replace the 60A fuse in the d-block with an 80A. Is this correct, or which size fuses do I need if not? Thanks.

IF you are running both amps at the lowest impedance they can run(usually 2 ohms) then you will be drawing that amount of current. if they're at 4 ohms, you'll draw 1/2 that. you are correct, you'll need a 150 amp fuse. (blade style, as you can't get a glass tube fuse that big) but there is another inherent problem. the power wires are WAAAAY too small for that kind of power draw. will it work? yes. but 4 gauge cable will create a voltage drop if more than 60 amps of cuurent draw is used @ 15ft to 18ft of length. if you were running 3 feet of 4 gauge, it could handle 300 amps, so distance is important. you should have the car wired with 1/0 gauge (looks like garden hose) and your amps will run better, without stressing the pwr supplies. then split it to 4gauge to the amps. 1/0 gauge ain't cheap, though, (around 6 bucks a foot) look for a GOOD car audio shop, as circuit of best buy won't have that. if you can't find 1/0 gauge (pronounced 'aught') do 2 runs of 4 gauge, one for each amp.

If the fuses haven't blown yet then you should be alright, but with that setup you do have the ability to blow them if you turn i up and leave it. I would buy a good bit of 4awg and do a second 4awg run back from the battery. If your current one isn't long enough to reach the amp then you would want a distro that has 2 4awg inputs and 2 4awg outputs, then just run both of the 4awg into it and run each output to each amp.

1/0 isn't that much either, locally it is but that's because locally it's a ripoff. You can get nice 1/0 power wire from www.darvex.com or www.knukonceptz.com for a little over $2/ft, or you can get 1/0 welding cable which will work just as well (but it will be uglier) for around $1/ft at www.weldingsupply.com.

as long as the strands are fine enough, sure you can save money. but i strongly disagree with the use of welding wire. current travels down the skin of copper, not the core, so the more strands you have, the better. i've measured it, and seen it with my own eyes...not all power wire is the same..

Short explanation is that the fuse by the battery is protecting your power wire from melting and not really to protect your amps. For more info on it go to www.bcae1.com and look at section 14 Fuses (and 16 Wire has some good info too).

In your situation I would be willing to bet a 125A fuse would be fine with your current wiring (that was almost a bad pun, sorry). But if you do start blowing fuses ever then upgrade to some 1/0ga or a second 4ga run (in that order of preference).

offset

Thanks for all the advice. I have looked into the bcae1 site a little more. Now my question is, It looks like they are suggesting a minimum wire gauge of 6 coming off the distribution block to the phoenix gold 4x100 amp. If I leave the 4ga coming off the battery, and the 8ga to the MTX which is a class D rated at 250 rms, what effect does this have. Seems like you would need the wire gauge to add up otherwise I would assume the MTX would lose allot of power. Is this correct, or could I get away with just switching the wire from the d-block to a 6 ga?

as long as the strands are fine enough, sure you can save money. but i strongly disagree with the use of welding wire. current travels down the skin of copper, not the core, so the more strands you have, the better. i've measured it, and seen it with my own eyes...not all power wire is the same..


yes it travels down the skin, the skin of the whole wire, not the skin of each individual strand. 1/0 will be able to conduct the same amount of current whether it has 10,000 strands or 1.

You're right, not all power wire is the same, the main differences are flexibility, appearance, and OFC won't oxidize over time while welding cable will. Other than that 1/0 is 1/0.

And besides, the welding cable you find at www.weldingsupply.com has thousands of strands, I can barely tell a difference in flexibility between the WS 1/0 and the darvex 1/0, and both of them work perfectly fine.