300amp fuse with 0 gauge wire?

[skittlesRgood 10+ year member]

so if you are only having 1 run of 0 awg from front to back and it will be powering the 90 fused amp , add the fusing on the kicker to the 90 and the total of those numbers is the size of the anl fuse you will need when kicker is added

thats what the guys at BB and such tell people. AKA hacks/morons/ people you never bring your car to.

going off of that... my 1000w cadence amp doesnt have any fuse on it so a 5amp fuse would be plenty rite????

listen to penn and the others, not BB.

 

[knukonceptz 10+ year member]

The fuse is there as a safety and to protect YOU in case of accident. As a result you have two options:

1) Fuse based on the max capacity of the wire.

2) Fuse based on system draw

#1 is fine for the main inline fuse, but in a dist block is down right silly. Most blocks use 4 gauge out, a 4 gauge wire that is 3' long can handle over 300A so fuse selection in a block based on gauge is not practical. It does not make the system better to use a 150A fuse on a 30A draw.

#2 from a safety stand point is more logical - Even if your amp lists three 30A fuses (90A) the ONLY time it will draw that is during a bass note/sweep. No normal music CD will create that kind of load, the beats too quick. Grab a clamp meter, you'll see what I mean.

What we recommend is to add up the system's total draw for the main fuse and then fuse each leg of a block according to the load on that leg. Reason for this method - safety! If you have 0 gauge running and a 300A fuse under the hood and 90A worth of draw, there is ZERO gain by putting a single 300A fuse in place of a 100A fuse. Under normal use, it makes no difference, but what happens in an accident? Why risk it if you have no need for it?

I am sure this is why MOST companies will tell you to fuse for the draw - safety. Just because your speedo says 160mph does not mean your car will go that fast

 

[dman4486 5,000+ posts]

The fuse is there as a safety and to protect YOU in case of accident. As a result you have two options:
1) Fuse based on the max capacity of the wire.

2) Fuse based on system draw

#1 is fine for the main inline fuse, but in a dist block is down right silly. Most blocks use 4 gauge out, a 4 gauge wire that is 3' long can handle over 300A so fuse selection in a block based on gauge is not practical. It does not make the system better to use a 150A fuse on a 30A draw.

#2 from a safety stand point is more logical - Even if your amp lists three 30A fuses (90A) the ONLY time it will draw that is during a bass note/sweep. No normal music CD will create that kind of load, the beats too quick. Grab a clamp meter, you'll see what I mean.

What we recommend is to add up the system's total draw for the main fuse and then fuse each leg of a block according to the load on that leg. Reason for this method - safety! If you have 0 gauge running and a 300A fuse under the hood and 90A worth of draw, there is ZERO gain by putting a single 300A fuse in place of a 100A fuse. Under normal use, it makes no difference, but what happens in an accident? Why risk it if you have no need for it?

I am sure this is why MOST companies will tell you to fuse for the draw - safety. Just because your speedo says 160mph does not mean your car will go that fast

then why does the speedo go that high?//content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[knukonceptz 10+ year member]

maybe the car manufactures are using the old "ILS" rating //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[dman4486 5,000+ posts]

maybe the car manufactures are using the old "ILS" rating //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

//content.invisioncic.com/y282845/emoticons/hilarious.gif.02a037aad04aa96f19982b298a3d70a8.gif

 

[n2audio 5,000+ posts]

Knu - I agree w/you 99%, and preach it routinely, but...

a 4 gauge wire that is 3' long can handle over 300A so fuse selection in a block based on gauge is not practical.

Voltage drop might be low, but at 300A heat would be out of control and the insulation would be melted in a hurry.

 

[knukonceptz 10+ year member]

What creates heat? - Resistance. If the resistance of 3' of 4 gauge passing 300A is less then the resistance of 20' of 1/0 at 300A you will have less heat created in the 4 gauge wire then you would with the 1/0 cable at stated lengths.

http://www.powerstream.com/Wire_Size.htm

4AWG Copper - 3' Long 12VDC @ 300A = 0.46V loss (3.83%)

1/0 AWG Copper - 20' Long 12VDC @ 300A = 1.21V loss (10.09%)

The 1/0 has twice the resistance in the above scenario due to length and amperage level

 

[n2audio 5,000+ posts]

for one thing - powerstream's V-drop calculator for 1/0 is wrong. 20' of 1/0 at 300A drops .59v

I just can't concede that a short run of 4 ga is safely going to pass 300A. I think that much current would heat 4 ga enough that the insulation would be melted in a few seconds. I understand a long run of significantly larger wire may have less total resistance, but in regards to thermal capacity of a wire I think resistance/length is the key, not just total resistance.

I know that on top of voltage drop when sizing a wire there is also circular mils/A to consider, and it doesn't take length into account.

 

[hemi=22s 10+ year member]

i always fuse the front line for the wires rated amps, then the distro in rear use manufacturers recommended fusing since my amps have no internals

 

[PSturmer 10+ year member]

i like no fusing //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[hemi=22s 10+ year member]

i like no fusing //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

well i like my 35k car too enuff to waste 10 bucks on fusing

 

[knukonceptz 10+ year member]

for one thing - powerstream's V-drop calculator for 1/0 is wrong. 20' of 1/0 at 300A drops .59v
I just can't concede that a short run of 4 ga is safely going to pass 300A. I think that much current would heat 4 ga enough that the insulation would be melted in a few seconds. I understand a long run of significantly larger wire may have less total resistance, but in regards to thermal capacity of a wire I think resistance/length is the key, not just total resistance.

I know that on top of voltage drop when sizing a wire there is also circular mils/A to consider, and it doesn't take length into account.

Pretty sure that calculator is accurate, regardless though, lets just take 4 gauge at 20' - Would you agree that 150A is a common limit put on 4 gauge? Then if thats true there is far less resistance in 3' of 4 gauge @ 300A then 20' of 4 gauge @150A

4AWG Copper - 3' Long 12VDC @ 300A = 0.46V loss (3.83%)

4AWG Copper - 20' Long 12VDC @ 150A = 1.53V loss (12.77%)

Without resistance, there is no heat. You need heat to melt PVC, if the 3' of 4 gauge is going to be "cooler" you will never have an issue. Its physics, not that I am good at it, but that is how it works.

 

[knukonceptz 10+ year member]

Just to compare calculators - use 24V since 12V is not available on all and you get pretty much the same numbers. You get the same voltage loss at 12/24/48V but the percent of the loss changes due to the higher base voltage

http://www.cerrowire.com/default.aspx?id=48

http://www.powerstream.com/Wire_Size.htm

http://www.csgnetwork.com/voltagedropcalc.html

 

[jrwalte 10+ year member]

What creates heat? - Resistance. If the resistance of 3' of 4 gauge passing 300A is less then the resistance of 20' of 1/0 at 300A you will have less heat created in the 4 gauge wire then you would with the 1/0 cable at stated lengths.
http://www.powerstream.com/Wire_Size.htm

4AWG Copper - 3' Long 12VDC @ 300A = 0.46V loss (3.83%)

1/0 AWG Copper - 20' Long 12VDC @ 300A = 1.21V loss (10.09%)

The 1/0 has twice the resistance in the above scenario due to length and amperage level

That's why I've never been concerned with installing another fuse at my distro block for my 4g to amp from 0g because it's length is under 2 feet and it could easily handle the amperage the 0g can provide from ~15 feet.

You'll see this concept in every day use. It's why your speaker VCs can have such a small wire. It's why your fuse holder can pass 300amps on a very thin piece of solid metal. Length has everything to do with how much a conductor can handle.

 

[n2audio 5,000+ posts]

My physics comprehension is fairly clear.

I'm not arguing resistance isn't part of the equation, I'm arguing it's not the only part.

And I still say the only application of resistance is PER LENGTH, not the cumulative total of resistance in a long run of wire, because it sounds to me like you're trying to say 100A through 100' of 4 ga is guaranteed to have thermal problems while 300A through 3' is ok.

After looking into it a little further.

Heat in electronics is a result of power dissipation - would you agree with that?

P= I^2 x R (Hmm, current is squared - seems like a much bigger factor than resistance...)

3' of 4 ga @ 300A ----- P = 300^2 x .00075 = 67.5w - or 22.5w per foot

20' of 4 ga @ 300A = 450w - or 22.5w per foot

You run the exact same risk of heat damage to the wire at a million feet as you do at a millionth of a foot.

Just for fun -

1/0 at 300A, 3' ----- R = .00029763, P = 26.8w, 8.9w/ft

1/0 at 300A/20' ---- R = .0019842, P= 178.58, 8.93w/ft

Let's just agree that we shouldn't be trying to run 300A through 4 ga at any length.