Doing the Big 3
Doing the Big 3 Almost finished wiring this stuff up and have a question or 2. I am using 4 gauge wire for all of it. The wire from the battery to the alternator needs to be fused according to the SoundDomain website. He states it needs to match the ampacity of the wire. What would be the correct rating fuse for 4 gauge wire? Also, is the wafer style fuses the correct type to use for this?
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From: Texas
A 4ga wire of that length can handle a lot more current then you’ll be using.
Its there mostly for protection of alternator short circuit which could be very dangerous in the event that wire finds ground since it is tied to the hot side of the battery. It can be even more dangerous when the engine is running. I would go with a 250+ amp fuse since it is just for short circuit protection and you don’t want to be stranded because the fuse was too small in the event of a voltage spike
Its there mostly for protection of alternator short circuit which could be very dangerous in the event that wire finds ground since it is tied to the hot side of the battery. It can be even more dangerous when the engine is running. I would go with a 250+ amp fuse since it is just for short circuit protection and you don’t want to be stranded because the fuse was too small in the event of a voltage spike
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From: Georgetown, DE
250+ amp fuse?? Are you nuts? 4 ga. wire has an ampacity of about 125 amps max. You want the fuse to blow before the wire starts a fire. SO any fuse larger than 100 amps is wreckless. That ought to be plenty for an amplifier of 1000W or less.
On The Tree
Joined: Aug 2005
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From: Wichita Falls, Texas
250 ... PLUS ... with a wafer fuse no less (very slow blow) can you say COOK! I usually take the values of the fuses for the amps I'm using and use that as a gauge. If you want to be on the safe side, go to the manufacturers site for the amps you're using and find the amp draw for the amps (usually given as a max amps) but the easy way would be find the highest fuse value and go with that (your amps are fused at 30 and 20 fuse your main around 50-60 amps, and that plenty within the amp handling of the wire) you never want to be anywhere close to the max amperage rating of a wire. Why run the risk of the fuses +/- rating to be on the + side and frying your wire and possibly smoking your car out or worse yet catching fire. Most fuses have a tolerance of +/- 10% (some as high as 20%- 40% depending on the manufacturer) so a 250 (+) amp fuse could possible be in the neighborhood of 275 amps + ( a BIG plus) ...
Like I said ... look at the MAX amperage you are "possibly" going to use and use that as a gauge. even if your are using bigger gauge wire than you need you still don't have to fuse for the wire ... fuse to protect your equipment ... and car.
Last edited by joe_kool315; Nov 30, 2005 at 08:56 AM.
That's why I ask this question. I know very little about amps and current and want to do it right. I don't want to catch anything on fire and I don't want to keep blowing a fuse that's to small. You guys keep discussing amongst yourselves and I'll check back later. 
Thanks for everybody's input so far.
Thanks for everybody's input so far. On The Tree
Joined: Aug 2005
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From: Wichita Falls, Texas
well for your specfic question ... you need to give us a little more information. What Amps are you using (manufacturer & model numbers), what are they fused at and will there be anything else on this 4 guage line from the battery (crossovers, lights, ...)? that way the input can be taylored to your specific set up instead of just "fusing" in general.
I would just hook up a multi meter where you are planning to put the fuse (in line) and crank up the stereo, find out how much current you are pulling and get a fuse 5-10 amps above that. I'd rather blow a fuse thats too small rather than melt my car.
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From: Georgetown, DE
Umm. That's if you happen to have a multimeter capable of doing dc current greater than 10 amps, which is the standard one most people have (if they have decent one at all).
Using the MFR specs for the Amplifier is better. And easier.
Must amplifiers come with installation instructions that will tell you what fuse and wire gauge to use for the power leads. If your buying a used amp, go to MFR website and download the instructions. Or call them and ask them what to use.
There is no harm with going with a larger gauge wire than the MFR spec. But you never, ever want to go with a larger fuse rating than the MFR spec. If you have more than one amp, run seperate power wires and fuses to each according to their individual specs.
Using the MFR specs for the Amplifier is better. And easier.
Must amplifiers come with installation instructions that will tell you what fuse and wire gauge to use for the power leads. If your buying a used amp, go to MFR website and download the instructions. Or call them and ask them what to use.
There is no harm with going with a larger gauge wire than the MFR spec. But you never, ever want to go with a larger fuse rating than the MFR spec. If you have more than one amp, run seperate power wires and fuses to each according to their individual specs.
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Verdad Gallardo TECH Senior Member
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From: Texas
Remember, we are talking about the hot wire that goes from the alternator to the battery.
This has nothing to do with how much amperage your amps are drawing. No matter how many amperes
your amplifiers demand, your alternator will only charge as much as it capable of.
The distance of the wire plays a big factor in how much current the wire can hold.
I suggested a 250 amp fuse so he is not stranded in the event of a voltage spike.
The alternator will never charge this much obviously but it is solely for the purpose of short circuit protection.
It is not uncommon to see north of 300+ amp fuses in stereo applications.
Just because it has a 250 amp fuse doesnt mean its going to pull 250 amps all the time.
The only time it would come close is in the event of a short circuit which is what this fuse is for.
This has nothing to do with how much amperage your amps are drawing. No matter how many amperes
your amplifiers demand, your alternator will only charge as much as it capable of.
The distance of the wire plays a big factor in how much current the wire can hold.
I suggested a 250 amp fuse so he is not stranded in the event of a voltage spike.
The alternator will never charge this much obviously but it is solely for the purpose of short circuit protection.
It is not uncommon to see north of 300+ amp fuses in stereo applications.
Just because it has a 250 amp fuse doesnt mean its going to pull 250 amps all the time.
The only time it would come close is in the event of a short circuit which is what this fuse is for.
I will be running one JL e6450 amp. It's a 450 watt 6 channel amp. It specifies a 60A inline fuse from the battery which I installed and it specifies to use a 4 AWG minimum power wire, which I did use. Remember, I am asking about the Big 3 upgrade mod and the one from the battery to the alternator specifically, not the amp to battery power wire. Thanks!
Originally Posted by joe_kool315
well for your specfic question ... you need to give us a little more information. What Amps are you using (manufacturer & model numbers), what are they fused at and will there be anything else on this 4 guage line from the battery (crossovers, lights, ...)? that way the input can be taylored to your specific set up instead of just "fusing" in general.
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From: Georgetown, DE
Originally Posted by 2MuchRiceMakesMeSick
Remember, we are talking about the hot wire that goes from the alternator to the battery.
This has nothing to do with how much amperage your amps are drawing. No matter how many amperes
your amplifiers demand, your alternator will only charge as much as it capable of.
The distance of the wire plays a big factor in how much current the wire can hold.
I suggested a 250 amp fuse so he is not stranded in the event of a voltage spike.
The alternator will never charge this much obviously but it is solely for the purpose of short circuit protection.
It is not uncommon to see north of 300+ amp fuses in stereo applications.
Just because it has a 250 amp fuse doesnt mean its going to pull 250 amps all the time.
The only time it would come close is in the event of a short circuit which is what this fuse is for.
This has nothing to do with how much amperage your amps are drawing. No matter how many amperes
your amplifiers demand, your alternator will only charge as much as it capable of.
The distance of the wire plays a big factor in how much current the wire can hold.
I suggested a 250 amp fuse so he is not stranded in the event of a voltage spike.
The alternator will never charge this much obviously but it is solely for the purpose of short circuit protection.
It is not uncommon to see north of 300+ amp fuses in stereo applications.
Just because it has a 250 amp fuse doesnt mean its going to pull 250 amps all the time.
The only time it would come close is in the event of a short circuit which is what this fuse is for.
TECH Senior Member
Joined: Apr 2004
Posts: 6,157
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From: Texas
Originally Posted by HiTechGent
He specifically asked about 4 gauge wire. You would NOT use 4 ga. from the alt to the batt. I can see using #0 or #00 ga. wire with a 250A to 300A fuse depending on the insulation material of the wire. Kynar or Teflon being preferrred.
The distance of a wire plays a big role in how much a specific wire can take.
The factory wire from the alt to the battery is 8ga but they put a 800 amp capable (cold peak discharge) battery on the car.
I guess the GM engineers should have ran double alt.
Again, to answer this question you have to consider.
Why is this wire there?
The answer is short circuit protection.
Your entire cars electrical system will be charged through this wire.
Just so were all on the same page here.
This is the wire from the alternator to the battery.
Choosing fuse sizes for your power wire to the back and specific amplifiers is a whole different ball game
Thanks for all your input on this matter 2Much. You seem to be in agreement with the post on http://forum.sounddomain.com/forum/u...c;f=5;t=007801 which I was reading earlier. You're right, there already is an 8 gauge wire in place from the battery to the alternator and it's not fused either, that I can tell. I was going to leave it in place and add my 4 gauge wire to it. All this is probably overkill for my application but I will probably do it anyway. I will put a 250A fuse inline and call it a day. 
Originally Posted by 2MuchRiceMakesMeSick
The distance of a wire plays a big role in how much a specific wire can take.
The factory wire from the alt to the battery is 8ga but they put a 800 amp capable (cold peak discharge) battery on the car.
I guess the GM engineers should have ran double alt.
Again, to answer this question you have to consider.
Why is this wire there?
The answer is short circuit protection.
Your entire cars electrical system will be charged through this wire.
Just so were all on the same page here.
This is the wire from the alternator to the battery.
Choosing fuse sizes for your power wire to the back and specific amplifiers is a whole different ball game
The factory wire from the alt to the battery is 8ga but they put a 800 amp capable (cold peak discharge) battery on the car.
I guess the GM engineers should have ran double alt.
Again, to answer this question you have to consider.
Why is this wire there?
The answer is short circuit protection.
Your entire cars electrical system will be charged through this wire.
Just so were all on the same page here.
This is the wire from the alternator to the battery.
Choosing fuse sizes for your power wire to the back and specific amplifiers is a whole different ball game
