How big the fuse should be?

I have a 75x4 amp that will get it source from a 4 gauge power cable. I need to fuse this cable and I am wondering how big should the fuse be? 60amp?

In the future, I might be adding another amp with a sub. Would this require even a more bigger fuse?

75w rms x 4 is usually about 60 amps of fusing. As a general rule, the size of your main fuse can be the same size of greater than that of the combined value of the fuses in the amp or amps. This fuse is not to protect the amp at all (except for some exceptions) but to protect the vehicle in the event of a short circuit.

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Top Secret, I can tell you but then my wife will kill me.

Would I need a bigger fuse if I add a second amp? Would this be calculated the same way, by combining all the amp fuses together? So if amp #1 has 60amp and amp #2 has 80amp, this will require me a 140amp fuse or something like that?

And I hear some people say to not get a bigger fuse than you need. Is it true?

vbel]A wrote:

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d I hear some people say to not get a bigger fuse than you need. Is it true?

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Absolutely. It's a safety thing. The fuse should be just large enough that it won't blow under normal operation, and small enough that if any little thing goes wrong with the wiring it'll blow. If your only fuse is at the battery like most installs I've seen, an oversized fuse will allow a wiring fault (insulation sliced on the B+ lead where it goes through a body hole) to dump gobs of current before the fuse will blow. Arcs like that reach thousands of degrees, and pose a significant risk in a moving evhicle. Not to mention the things that happen to a battery when it's shorted, even for a short time (sulfuric acid vapors, burst cells, spilled electrolyte, etc). It's not something you want to mess with.

Having been on the wrong end of several serious electrical accidents due to other folks not following established practices I tend to be conservative on safety. That doesn't mean you should dismiss what I say, only that I've had the right ways reinforced through experience.

-dave

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This is not a sig. This is a duck. Quack.

The combined value of 140 amps is the correct assumption. Now what you are hearing can be taken a number of ways. In 99% of the cases, the fuse has nothing to do with the amplifiers, remember though there are exceptions and we'll get to that. Even if you had a 140 amp fuse up front, under what circumstances are you going to be drawing this much current and for what continuous period of time. Most fuses are rated to pass much more current safely for breif moments, it is when they are asked to pass a large amount of current for a sustained time that they will blow. Now with the exception still outstanding, if you are the kind of person who is going to play the system long and hard and annoy just about everyone, chances are that a large value fuse will be necessary, if you want to listen to the system at a moderate yet sustained level a large to mid value fuse would be used. If you listen to a system that has 140amps of fusing at the amplifiers and want to listen to this system and don't plan on turning it up, you will be drawn and quartered.

The only problem with a fuse too small is that it may blow if it asked to do a job it was not designed for. If the fuse is too big, so what, the amplifiers will only draw what they need through it. Like I said with the exception still outstanding, the purpose of this main fuse is to protect the vehicle and it's contents in the event of a short circuit, most commonly cause by the power wire grounding out, might be do to chaffing or a nasty car accident.

Now for the exception, some amplifiers, like the older Rockford, Precision, Lineap Power, Orionand even Alphasonik did not have built in fuses. The manufacturer recommended to use x size fuse at the battery. This still meant that it could be fused at the back by the amp and a single large fuse at the battery, but this is the exception to above. Hope this helps out.

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Top Secret, I can tell you but then my wife will kill me.

I have always liked to run a seperat line for each amp when possible and this is why. Do you know how long you can dead short a wire with a 150 amp fuse inline. Probally long enough to weld together a bike frame. If you have smaller fuses like for example a 60 and an 80, then if something gets dead shorted its gonna blow a lot sooner and hopfully not cause as much damage.

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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

Wow, 2 power cables is an overkill I think. You are the first one I hear that uses 2 cables. I'm not exactly sure if this is really needed..cause then everyone would do it.

And lots of us have.......

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Top Secret, I can tell you but then my wife will kill me.