power wire fuse

How far from the battery should the fuse be installed.. i only have 1 fuse till i get teh other one for back. by amp.. so for now im just running the one by the battery.. Does it have to be so far away form the battery or can i make the 1st lead like  3 inchs way from battery? then fuse then rest of wire??

Fuse within 12" to 18" of the battery. If you can get it closer, fine. The fuse is to protect the WIRE. I do 60A for 8 AWG 100A for 4 AWG, 200A for 2 AWG, 300A for 1/0AWG. Fuse anytime you change wire guage.

The fuse is not for the wire, it is for the car. Fusing circuits has only one objective and that is to protect the car from a fire in the event of a short circuit. The rating of the fuse should be that of the maximum load on that circuit. The wire must be of the correct gauge to safely handle that current over the length of the wire run. By law, the fuse must be no more than 18 inches away from the power source. If you are only running one component off this wire, then you do not need another fuse at the rear. The reason amps have fuses in them is to prevent an internal short/defect from affecting the power feed input. Always make sure that the wire gauge is correct for the fuse rating otherwise the wire becomes the fuse. The ground cable for the cicuit must be the same size as the power cable.

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sparky

"The fuse is not for the wire, it is for the car. Fusing circuits has only one objective and that is to protect the car from a fire in the event of a short circuit"

It is very much implied that the protection applies to both vehicle and wire as a cause an effect relationship. Yes the wire must of proper guage but also of proper protection. The battery fuse is not ment to protect the amp or other equipment downstream. This specific fuse is to protect the vehicle agaist fire by protecting the WIRE.

Ditto.

The primary aim of a fuse is to protect what is immediately downstream of it - ie, wiring; or the equipment it its an "equipment" fuse.

Hence a n-Amp cable needs a fuse of n-Amps or less protecting it.

That doesn't preclude fuses of much less than n-Amps being used.
But you wouldn't use a 20A fuse to protect 15A or 10A cable etc.

Fusing for the "load" aka wire or equipment is protecting the "car".

Its OVER-CURRENT protection, lets keep it that simple.

AudioCG's comment to fuse when changing wire size is key. You should have to, if you're doing it right.

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This is what I do for FUN!

i got a 300 amp breaker fuse about 2-3 inchs from front battery Useing 0 gauge wire hooked just to one amp... so Im good to good ?  i dont need a fuse in back?

You only need a fuse to protect the downstream stuff.
IE - the 300A fuse protects the 0G (though powerstream.com say the max 0G current for chassis wiring is 245A -0 if so, the cable may flame before your fuse blows....).

You add other fuses as required, but usually amps have their own fuse(s).

A 300 amp breaker is too high. Find out what the maximum current your amp is designed to safely handle and put that same size fuse up front. If you have more than one device on the end of the circuit, then add up the current ratings and that will be your fuse size at the front. This can continue until you reach the current capabilities of the wire runing front to back. Using a 300 amp breaker for one amp is dangerous. A slight short circuit in the wire could cause a fire before the 300 amp breaker blows. Ask yourself this: Do I want to replace my vehicle or my amp,this will help clear your mind when making the right decision.

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sparky

Ditto.
Not that I like hi-current DC circuit breakers - fuses are bad enough.
(I've seen 3kA & 6kA DC protection EXPLODE... )

The amp dont have a built in fuse..  and it calls for a 300 amp.. im just doing everythign by the book..

A ~3kW amp?
Funny that they don't supply it.....

I think you may need 000 gauge cable though.... else 2 lots of 2G. (And don't forget your GNDs!!)

got 0 gauge power adn ground.. made by monster

So does 0G handle 300A?
HERE says 245A.
300A will generate 50% more heat than 245A.

In a 12V system 1/0 AWG will handle 300 amps. The site listed above says their ratings are conservative. Short Distance, not bundled and not in conduit. You are running a single wire with 90C or 105C jacketed copper. The load is not 100% duty factor and in less than 20 feet in most cases.

Thanks ACG.

Amazing as it sounds, I never use such tables (except for mandated stuff - but that's usually AC and rarely if ever 12V-24V DC etc) - I go by resistance etc.
Though I might sanity-check with certain handy tables....

But isn't 20' too long for heat conduction?   2' ok, but 20'?
(That's more of a general inquiry - 10W per foot at 300A isn't too bad for 0G... - I'd guess warm, but far from hot.)