1st gen 105 amp bolt in alternator.

Assuming the wires are the same distance and makeup (strand type).

 

Like @Gen1FTMFW said,you're just looking to protect the wire. For that distance, 6 gauge wire is rated for something like 150-200 amps. I'd probably fuse it somewhere in that range.

 

Perfect, thank you both of you for this info, I appreciate

 

It might be worth thinking about what order the fuses would blow should there be a short. For example, if the 6ga wire shorts and its fuse blows at max load, what happens to the fuse on the 8ga?

I don't think its a problem, but it would be good to be aware of.

I would want to fuse it so that there is no way to overload the altenator. I don't know what happens exactly to an alternator shorted to ground, but its not going to be good.

 

Fuse protects the wire... Select a fuse based on wire. Smaller than rated is fine.

 

So now I’m confused,
4 post above was stated to use 150-200 Amp with the 6 gauge cable.
And this chart says 80 Amps,

So what’s the correct fuse to use?

 

Maybe this will help... its important to understand that you are trying to protect the wire with your fuse. you go higher on the fuse than what the wire is rated for, the fuse will not blow and the wire will send you into a car-BQ. At least that is what I've learned (Ive been working on building a Bussmann RTMR up in the engine bay and also taking power to an AUX panel in the bed of the truck).

see the section on "Fuse Opening Time"
http://www.bcae1.com/fuses.htm

 

there is zero need to get a fuse that is rated significantly higher than the max amperage output of the alternator. Go with a 120 amp fuse and you will be fine. If you alternator starts having problems, it will pop long before the alternator burns out. Not only is a fuse to protect wires, it's also going to protect the components as well. And the components are an important piece of the puzzle.

 

It sounds to me like you can just run a fused 8 gauge wire in addition to the stock 8 gauge wire, which will split the current evenly to 52.5 amps for each wire, well within the wire's limits, correct?

 

Which of these tables is correct? Lots of conflicting information!

The last table nearly implies that the stock 10 ga wire is fine.










Which of these tables is correct? Lots of conflicting information!

The last table nearly implies that the stock 10 ga wire is fine.

 

right and the fuse blowing before the wire is compromised will protect your components.

The very short length in this case may definitely change things. @1997tacomav6 definitely research. I was just trying to put out the part about wire size and fuse rating.

 

Ok, in this case it’s better to be safe, so I will install a 100 or 125 amp fuse

 

where did you get this table from? This nearly implies that the stock 10 ga wire is sufficient at such a short length..

 

I guess I should read the entire thread but why are you going with #6 instead of #4? Just curious...

 

he's running 2 wires from the alt to the battery.

 

X2

 

It was just a google image search. If I were actually building a system, I'd use the resources from the blue seas website...

http://circuitwizard.bluesea.com/

 

Because we're talking about two parallel wires being run, you're not really getting protection for any other components unless you were to fuse the two wires to where the combined fused current is just over the alternator output. But I would agree that generally the best thing to do is to select a fuse size slighly over the anticipated maximum load.

Since there have been so many questions on wire sizing for a given current....

There are two major issues you have to consider when sizing wiring.

• Voltage drop
• Temperature rise

For short runs, voltage drop will not be the controlling parameter. For longer runs, you need to determine an acceptable voltage drop (3% is probably the most conservative value) and size accordingly.

Temperature rise is much more complicated. You need to consider the ambient temp, insulation max allowable temp, various parameters related to heat transfer (conductive coefficients, installed location, wind speed, natural vs forced convection, etc..). Given how complicated this is to do (and how it's not an exact science in most applications) various approximations are used. I've seen 300 amps per circular mill as an (albeit conservative) recommended value for chassis wiring. Given that 6 gauge wire is 26,251 circular mills, you can start from there and select a value you feel is appropriate.

 

Going to stick with what I said before... fuse FOR the wire. Not trying to turn this into an argument but don't go higher than what your wire is rated for.

If it were me, I'd got with 4 AWG and 125A fuse.

This is a good explanation -
https://www.stevemeadedesigns.com/board/topic/207673-fuse-for-big-3/?do=findComment&comment=3153507

 

Sub