i have a question about fuses....

[smoka 10+ year member]

Why buy 1/0 wire and fuse it at 125A?

If your load is 125A, then why fuse it higher? Better to blow the fuse quickly???

Most people get oversized wire because of the lesser voltage drop, and also for future upgrades.

 

[jpexpc 10+ year member]

If your load is 125A, then why fuse it higher? Better to blow the fuse quickly???

Why not just run smaller gauge wire? There are reasons for this........

 

[smoka 10+ year member]

my new question was what fuses should i be running at this fuse block... http://www.knukonceptz.com/productDetail.cfm?prodID=KNF-12 for a system that is 900 watts rms- 1100 watts rms.. and i dont see 250 amp //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Instead of using theoretical power output. It would be easier to pick your fuses based on the fusing on the amps when buying that distro block.

Ex. If one amp has 3x20amp fuses and the other amp has a total of 2x20amp in fuses, the just buy one 60 and one 40 fuses for the distro. Then, near the batt put one 100amp fuse leading out to the distro.

 

[gnatnoop 10+ year member]

Instead of using theoretical power output. It would be easier to pick your fuses based on the fusing on the amps when buying that distro block.
Ex. If one amp has 3x20amp fuses and the other amp has a total of 2x20amp in fuses, the just buy one 60 and one 40 fuses for the distro. Then, near the batt put one 100amp fuse leading out to the distro.

THANK YOU!!

 

[lantz 10+ year member]

Instead of using theoretical power output. It would be easier to pick your fuses based on the fusing on the amps when buying that distro block.
Ex. If one amp has 3x20amp fuses and the other amp has a total of 2x20amp in fuses, the just buy one 60 and one 40 fuses for the distro. Then, near the batt put one 100amp fuse leading out to the distro.

thats right,sorry about that...i dont use distibution blocks and im not used to having small amps.i always fuse big between each battery and between my last battery and amp is a big fuse considering it pulls almost 450 amps at full tilt.

and kyle,next time you say somebody is wrong,stand up and explain yourself...dont leave it for somebody else to do!

 

[McIntosh 10+ year member]

Sorry guys, but I disagree.
If you know what the max continuous load is, then you fuse to protect the equipment.

Here is how you calculate your fuse size:

You take your max continuous load, which is 200a in the example above. Multiply that times 20% to get your correct fuse size. So you would use a 240a (or 250a) fuse for the above example. 20% is a 'rule of thumb' that electricians often use. (the details can get pretty technical)

If your correct fuse size is less than the max ampacity of the wire, then use it. If its higher, then you need to upgrade your wire.

Between the alt to batt, and amps to batt, you can easily calculate the fuse ratings, so why would you oversize it?

Fuses are to protect the conductors, not the equipment. Where your 20% "rule of thumb" comes from I've no idea. 125% is a rule (without the thumb) and is applied in the conservative direction (ie conductors rated for 125% of load). For motors, not car stereos.

 

[AlterEgo99 5,000+ posts]

Fuses are there to protect the conductor (wire) first, the equipment second. That is why it is suggested that you locate the fuse as close to the power source (aka battery) as possible. This way, if there is a short, the liklihood of a fire is minimized.

It is correct to state that you should fuse based on the wire gauge, IF you have no information as to what the equipment connected to it requires.

My '08 Silverado has a stock 175 amp fuse for the the main line between the alternator and the battery. That was with stock 4 gauge wire. When I went to the Big 3, I replaced all of the 4 gauge with 0 gauge. I kept the fuse at 175 amps. It is much better and smarter to stay the same or even go a little smaller if you are not sure of the overall load. Better to pop the fuse and then step higher than putting in too large of a fuse and end up with your car burning to the ground.

I only have a 1000W RMS system, and each Alpine amp contains fuses at the amp itself. However, I still fused each power wire at the battery for each amp based on the total amperage of the fuses on each amp. One totals 60 amps, the other totals 80 amps, so a fuse on each power lead to the battery at the battery, one for 60 amps, the other for 80 amps.

Fuses are pretty cheap insurance when you think about it. And it is always better to go too small than to large. Most equipment manufacturers will list the rated amperage for their equipment (amp). If you don't know, call their tech support line or better yet, check Crutchfield.com. They carry a lot of the amps you may buy and they always list the fuse size in their on-line specs. Or post the question here...there is always someone who will know.

 

[MakeshiftAudio 10+ year member]

I say fuse for the equipment, as long as you have the sufficient size of wire for that given load.

1000kcmil 545A

750kcmil 475A

600kcmil 420A

500kcmil 380A

400kcmil 335A

350kcmil 310A

300kcmil 285A

250kcmil 255A

4/0 230A

3/0 200A

2/0 175A

1/0 150A

1 110A

2 95A

3 85A

4 70A

6 55A

8 40A

10 30A

12 20A

14 15A

These numbers may seem weird, but are rated for 100% duty/constant use.

This is not fuse rating, this is the maximum current rating for the wire.

 

[Lakota 5,000+ posts]

Fuse amperage ratings are such a joke. Just throw something in there between the values of 200-300A. It's not like fuse tolerance is that great, anyways.

 

[blackman 10+ year member]

ok, i have another question for you guys....if i get this kit.. http://www.knukonceptz.com/productDetail.cfm?prodID=KFX-PK20

which fuses should i get if i am running about 900-1100 rms

if ur getting only 1100 rms u could go with a 150....it actually should depend on wire size and the watts of your amp.....depending the amp, I have an audioque 2200 the fuse it requires is 300 amps because of the power it can do at 1 ohm or .5 ohms, now i just got a 2nd amp so now i must run (2) 300 amp fuses, if I had the AQ1600 I could get away with a 250 but maybe a 200 amp fuse?, then if i go with the 1200 I could use a 200 amp maybe a 150 amp fuse.... basically take the fuse and times by 10 and thats how many watts u should maxx it at.

100AMP = 1000w

150AMP = 1500w

200AMP = 2000w

250AMP = 2500w

300AMP = 3000w

idk your setup but u could try and use just a 150 first, and if it blows the fuse then go with a 200.

 

[blackman 10+ year member]

Instead of using theoretical power output. It would be easier to pick your fuses based on the fusing on the amps when buying that distro block.
Ex. If one amp has 3x20amp fuses and the other amp has a total of 2x20amp in fuses, the just buy one 60 and one 40 fuses for the distro. Then, near the batt put one 100amp fuse leading out to the distro.

depending on the amps.....he might not have external fuses....

 

[smoka 10+ year member]

Fuses are to protect the conductors, not the equipment. Where your 20% "rule of thumb" comes from I've no idea. 125% is a rule (without the thumb) and is applied in the conservative direction (ie conductors rated for 125% of load). For motors, not car stereos.

Of course fuses ARE to protect the conductor. But to put larger fuses than the load requires is pointless.

Since you are an electrician, when you run wires you often have no clue what the load will be. You don't know what someone will plug into and outlet so you just put in a breaker based on the wire size.

But when designing an electrical system, I know exactly what the max load is. In the case of a single car amplifier with a 100amp built-in fuse connected to a 0ga wire. If that amp is the only thing on that wire, then the max load will be 100amps and you will NEVER want to see anything over that on the wire. So you would be dumb to put anything more then a 100amp fuse at the other end of the wire near the batt.

Either way the point is that fuses are sized to be larger than the max load which I'm sure the average CA guy doesn't know.

 

[bw_audio 10+ year member]

..

 

[McIntosh 10+ year member]

Of course fuses ARE to protect the conductor. But to put larger fuses than the load requires is pointless.
Since you are an electrician, when you run wires you often have no clue what the load will be. You don't know what someone will plug into and outlet so you just put in a breaker based on the wire size.

But when designing an electrical system, I know exactly what the max load is. In the case of a single car amplifier with a 100amp built-in fuse connected to a 0ga wire. If that amp is the only thing on that wire, then the max load will be 100amps and you will NEVER want to see anything over that on the wire. So you would be dumb to put anything more then a 100amp fuse at the other end of the wire near the batt.

Either way the point is that fuses are sized to be larger than the max load which I'm sure the average CA guy doesn't know.

Point well taken. I know you're not the average when it comes to knowledge on this website, your posts prove otherwise. I didn't intend to belittle you by any means. The ampacities that are posted (by others) FAR EXCEED the code maximums. Using a lesser rated fuse can never hurt (other than annoying blown fuses killing your tunes). Every amp I've ever owned was fused from the factory. If those fuses blow, Houston we have a problem (in the amp most likely). You are absolutely correct in saying there is no need to fuse above expected current. I'm more concerned about people using too large a fuse. Your last sentence: Either way the point is that fuses are sized to be larger than the max load which I'm sure the average CA guy doesn't know, is of concern. It sort of implies that you fuse according to the load. You MUST fuse according to the wire size, not the load. I'm quite sure you know better, but some 16 year old kid will read it differently and burn down his Honda. For some strange reason, people here seem to think that a shorter wire can carry more currrent than a longer wire. I know (and I assume you do as well) this is total BS. The "car audio bible" sites are full of absolutely incorrect information these people seem to take as Gospel. They sell their wares that way. A salesman trying to sell you his goods is like a hawker at a carnival: he has his eyes on his mark. PT Barnum wasn't wrong.

 

[smoka 10+ year member]

If only someone had the right equipment to bench test several car audio power wires. It would be interesting to see how much current they can run before they melt....