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Discussion Starter #1
Sometime this weekend I hope to install my 2nd amplifier. As such I now have a fused distribution block, but I am not 100% clear on what size fuses will be OK to use.

I will be running an Alpine MRD-M605 and MRV-F345, both have their own fuses. Currently I am just running the F345 on some 8 gauge wire, with a fuse a few inches from the battery (can't remember the rating, but will look and post later).

When I put in the second amp, I plan to pull the 8 gauge power wire and replace that with some 4 gauge, and then use the 8 gauge to come out of the distro block to the amp. I will keep my inline fuse near the battery, and also have 2 x 50A fuses for the distro block.

Is all that OK? Or should I get larger fuses for the distro block? And, possibly the inline one depending on what size that is.

Thanks.
 

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Discussion Starter #3
OK, so it appears that the inline fuse is only a 60A, should I change that out for a 100A? or is that large enough? I don't mind having to change it out, but if I don't need to, then I won't.
 

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Keep in mind that if you're using the amp at less than its full rated power (say, a 2-ohm stable amp at 4 ohms), it won't draw the max current.
 

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You'll be fine with that as others stated. Keep in mind, you are fusing the wire, not the amps.
 

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Right you are fusing the wire so for 4ga it could be much larger than the 8ga wire fusing. However there is little point to running fuses way larger than you need. The idea with large wire is that it keeps the voltage higher for the amps under large draws, when you wire over distance (to your trunk/etc). A smaller fuse will always pass more than rated for a short time and usually only sub amps playing bass music get close to blowing the fusing in them. You should not need a main fuse that adds up to what is in the amps, but you can put how ever large a fuse that wire will safely handle if you need to.

For example I forget what fuses it had a photo would show, but I had a kicker 700.5 running 4x70rms 4 ohm and 1x420 (class D) 2 ohms. I played some bass music with the highs near clipping and the bass (level) about maxed out it didn't seem to clip much by ear. This was on quad 12s IB rated for 600rms. I got a max clamp reading of 74A on the power wire and RMS reading of around 40A. It had a 5ga amp kit good for about 1Kw class D likely less on class AB amps. Have different amps in now I keep changing them, but the main fuse is 100A I should go smaller just keep forgetting. I don't beat it regularly and never normally played it that loud with the kicker I could not hear the highs like that. I am sure a 60A would have been fine on the kicker possibly even a 40A for me though it somewhat depends on use and I would play it loud once in a while just not at max sub level.

To simplify remember a long wire with DC power will reduce voltage before it reaches the max power it can safely handle. A fuse will just blow. It is because wire has a resistance per foot that adds up over distance and a fuse is very short. And amp makers like to put the very largest fuses they might ever possibly need lol. I've seen a lot of blown amps with good fuses in them.

Fuses are in case of shorts, the smaller you can use the better.
 

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Right you are fusing the wire so for 4ga it could be much larger than the 8ga wire fusing. However there is little point to running fuses way larger than you need. The idea with large wire is that it keeps the voltage higher for the amps under large draws, when you wire over distance (to your trunk/etc). A smaller fuse will always pass more than rated for a short time and usually only sub amps playing bass music get close to blowing the fusing in them. You should not need a main fuse that adds up to what is in the amps, but you can put how ever large a fuse that wire will safely handle if you need to.

For example I forget what fuses it had a photo would show, but I had a kicker 700.5 running 4x70rms 4 ohm and 1x420 (class D) 2 ohms. I played some bass music with the highs near clipping and the bass (level) about maxed out it didn't seem to clip much by ear. This was on quad 12s IB rated for 600rms. I got a max clamp reading of 74A on the power wire and RMS reading of around 40A. It had a 5ga amp kit good for about 1Kw class D likely less on class AB amps. Have different amps in now I keep changing them, but the main fuse is 100A I should go smaller just keep forgetting. I don't beat it regularly and never normally played it that loud with the kicker I could not hear the highs like that. I am sure a 60A would have been fine on the kicker possibly even a 40A for me though it somewhat depends on use and I would play it loud once in a while just not at max sub level.

To simplify remember a long wire with DC power will reduce voltage before it reaches the max power it can safely handle. A fuse will just blow. It is because wire has a resistance per foot that adds up over distance and a fuse is very short. And amp makers like to put the very largest fuses they might ever possibly need lol. I've seen a lot of blown amps with good fuses in them.

Fuses are in case of shorts, the smaller you can use the better.

Isn't it always better to place the biggest fuse the power wire can handle to keep resistance low?
 

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Isn't it always better to place the biggest fuse the power wire can handle to keep resistance low?
You might if you do SPL comps and look for every last spec of power, but since the fuse wire is so short the resistance it offers is tiny.

Yes resistance of the fuse melts it in the end, but it is made to melt. Fuses don't often get warm unless the current is steady and near maximum, just the perfect conditions...and steady has no place in music excepting a pure sine wave. It does not take much resistance on 30A of current to start making a lot of heat. Resistance on larger current is always given away by heat.

So while you are right, conditions would have to be perfect to have the resistance of a fuse lower the voltage without blowing it, they are made to go one way or the other (example: closed in for no cooling). IMO the fuse holder can offer much more resistance if not in good condition, with ATC fuses.

On top of that you need a significant voltage drop to actually affect dB output at the speakers.


Note the last part at the bottom
FUSES
 
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