What Size Fuse To Use?

120 amps should do very well for that amp in most length runs.

 

You need 2 types of fuses:
1) One located at the amp, to fuse protect each individual amp. Most amps have them built in, you don't need to augment these with external fuses in the rear of your car. This fuse protects the amp from any overdraw situations.
2) One located on the main power wire, 18" or less from the battery. This fuse protects your car, battery, and wiring from any situation resulting in a short circuit on that main power wire - whether that's a screw through the wire, friction rubbing the casing off, or a loose connection. The short circuit will cause hundreds of amps of current to flow, popping the fuse up front, before any damage can be done. This fuse needs to be at least as large as the sum of all your fusing at the rear of the car, and I like to factor in another 5%-10% just to cover any current that might be lost to resistance in the main wire.
So, your underhood fuse needs to be at least the sum of your fusing in the rear, and can be quite large - the larger it is though, the greater your risk if a short actually develops. I'd suggest your total fusing plus 5%-10%, personally... but if you purchased say, the Audiopipe 1/0 kit that includes a 250a fuse - then go with it, no harm done.

 

For the main power line I generally add the total wattage you are running and then divide by 10. Only if you do not know your amps' maximum amperage though. By dividing by 10 instead of 14.4 you factor in the loss due to the amps not being perfectly efficient and add a little more for just in case.

 

I cant believe geo just typed that......


the Main Power Fuse should have NOTHING to do with your Amps NOTHING....

the Main Power Fuse should be Fused at the Total Max Amprage Rating for the Gauge and Length of wire your Running... PERIOD.....

After all, this fuse is to protect the WIRE not the Amps........

grated if your using the proper wire in the First place this should be a Number Larger than all the Amps Power Requirements anyway. However I never Assume.

 

So let me get this straight, Michael is saying to fuse the main power wire at the MAX amerage rating for the guage wire being used? So for 0/1 awg wire, for instance, you'd want to use a 325 amp fuse and that's it?

I am not saying that what's written at bcae1.com is gospel, but he says to use a fuse that is somewhere in between the max amp draw the wire can sustain and the max amp draw of your amp(s). Maybe I misunderstood that. He also stated to add inline fuses anytime you drop down to a lower guage, like at a dist block.

 

James, I believe by "sum of all your fusing" Geo means the sum of all your amps' max current draws, which right now is just your one amp. But you might as well prepare for the future when you have 2 amps. I doubt another 75x4 amp will really draw that much current (30-40 amps tops maybe?)

I think a better question is if you actually need a fused dist block or not. I think that depends a lot on what fuse you have on your 0/1 awg wire. If you put a 120 amp fues on your 0/1 awg wire, for instance, your 4 gauge wire after the dist block could handle that much current. So if one of your 4 awg wires got a short, the main fuse on the 0/1 wire would pop. But if you had a 200 amp fuse on your 0/1 wire, for instance, then you'd need to add fuses either at the dist block or somewhere on the 4 awg wire going to your amps. Someone correct me if I'm wrong about this.

I am still blown away that your amp has five 30-amp fuses installed into it.

 

in reality if you get a short in your Line you will be Drawing in excess of 500amps (depending on your amprage of your battery)probally anyway. so fuse rating it more or less irrelvant anyway...

However, When your Placing fuses on a Item to protect it you do so based on the Specs for the item your Protecting, not Items that may be attached to it

Forexample. you dont see household Outlets with Breakers for 2amps because the appliance you may attach can only handle it, no theya re rated for normally 15-25 because that is what the wires and outlets can support then the applianices have there own fuses


same thing here

the main fuse is there to protect your wires, so the fuse should be relfected as such

the Manufacturers in most cases supply on board fuses to protect their devices


Clearer now???

 

What I mean is, if you install a fuse that's smaller than the sum of your amp's individual fuses, you run the risk that during normal operation - that is, any operation not blowing fuses in the back - you could blow the fuse underhood.

The higher you go above that, you start to run the risk of "what happens if it's a short circuit... but to a painted surface with a little resistance?" etc.
You simply have additional risk that the fuse won't blow, or at least as quickly.

But, I did make the point that the 250a fuse that the 1/0 wiring kit includes is just dandy to go with, no worries about it being "too large".

And you may be getting your wire for free... but you need a great many other things - distribution block, fuseholder, fuse, connectors, etc. It's not a freebie, ever.

 

So he should not have to put a 325 amp fuse on his 0/1 power wire as I think you suggested above, right? (0/1 awg wire can safely handle around 325 amps max if I am not mistaken). Seeing James' max draw would likely never surpass 200 amps (I really doubt it would ever break 100 amps even when he gets 2 amplifiers), he could add a 120-150 amp fuse on his main power wire and be ok. But he would also want to add either a fused dist block or some inline fuses on the 4 awg wires going to his amps. Keep in mind fuses cost money and the bigger the fuse the more the cost. So we are trying to keep his costs down by utilizing the smallest fuse possible while staying safe.

All I know is that I added 140 amp fuses on my main power wire since that is the absolute max draw of my two amps and anything above that likely means a short somewhere. Maybe I have this all wrong, which would not be the first time. My system works, which is all I care about!

 

OK, I think I have it now. Like Michael said, once you get a short, you would be drawing a current of 500 or more amps, so having a 200 amp fuse or a 250 amp fues really makes no difference at all. He just need to be above the max draw of his amps and below the max draw that 0/1 awg wire can safely sustain.

In addition, he will need to fuse his 4 awg wire to protect it.

So to make James' life as simple as possible, let's make a "fuses summary" for him:

He needs a fuse for his 0/1 awg wire, say 200-250 amps.
He needs a fused dist block to protect the 4 awg wire going to his amps, with a 100-125 amp fuse for his sub amp and a "X" amp fuse for his future front comp amp.

P.S. I wanted to address his amp having 5 30-amp fuses. Just because his amp has these fuses does not mean it will ever draw 150 amps. Likely its max current draw is below 100 amps, right?

 

That looks to be the proper fuse setup you want. Maybe someone will chime in and second this emotion.

 

For the underhood fuse - essentially yes.
For the fuses in the rear - it's imperative that your amps have their correct fusing installed... if five 30 amp fuses is that - then so be it.
But it does seem a bit suspicious.. I know of monsterous gigawatt monoblock amplifiers that have lower value fusing. Might want to verify it, that's all.

 

The 5 30-amp fuses are built into his amplifier, but I seriously doubt he needs a 150 amp inline fuse on the 4 awg wire leading to his sub amp. 4 awg wire can safely carry a continuous current of 150 amps, right? (might even be 125, I have heard both). Anyway, I think a fuse in between 100 and 150 amps on his 4 awg power wire would suffice.