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Old 07-18-2009, 11:19 AM   #1
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HELP with fuses

ok i have a jl audio 300/2 watt amp with 8 awg cable. the amp kit came with a 40A AFS fuse.

the fuse blew yesterday and im looking to buy a new ;one.

i bought a 80A fuse today for a few dollars and i am wondering if i can use that without causing any damage to my battery, amp cables or my actual amp???
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Old 07-18-2009, 11:27 AM   #2
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NOOOOOOOOOOO!!!!!! only use the rated fuse. any bigger and you could risk blowing up your amp. any smaller and you will go broke on fuses.
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Old 07-18-2009, 11:30 AM   #3
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Only replace fuses with the same size that was there before.
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Old 07-18-2009, 11:44 AM   #4
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WRONG
All of you.

You're fusing to the max amperage of the cable. The amount right under where the cable melts its jacket and catches something on fire. Thats when you want the fuse to blow. For 8awg, ampacity is at 75a. Fusing with an 80a might be pushing the limit of safety if the run is longer than 8ft. You can safely fuse up to 60A on anything longer than 8ft.
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Old 07-18-2009, 11:50 AM   #5
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so ur saying disregard when the amp says the fuse rating is and use what fuse if for the size of cable?? always thought the fuse was to protect the component, not the cable.
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Old 07-18-2009, 11:59 AM   #6
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Quote:
Originally Posted by johnecon2001 View Post
WRONG
All of you.

You're fusing to the max amperage of the cable. The amount right under where the cable melts its jacket and catches something on fire. Thats when you want the fuse to blow. For 8awg, ampacity is at 75a. Fusing with an 80a might be pushing the limit of safety if the run is longer than 8ft. You can safely fuse up to 60A on anything longer than 8ft.
so say he had 4 ga wire should he put an even larger fuse.
I think not, go with what the anp manufacture recomends.
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Old 07-18-2009, 01:23 PM   #7
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Johnecon2001 is correct. The OP is replacing the fuse in the power cable. That fuse is meant to protect the cable and the vehicle, not the component (amp). The fuse in the component protects the component. If the OP had a fuse blow on his amp, then he should replace it with the same size fuse that the amp originally came with from the factory. For the power wire, an 8awg cable should have around a 60A fuse. 4awg I stick with 80A, but the wire has ampacity for more current. 80A's are just easier to find.
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Old 07-18-2009, 02:00 PM   #8
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Quote:
Originally Posted by sooner07 View Post
Johnecon2001 is correct. The OP is replacing the fuse in the power cable. That fuse is meant to protect the cable and the vehicle, not the component (amp). The fuse in the component protects the component. If the OP had a fuse blow on his amp, then he should replace it with the same size fuse that the amp originally came with from the factory. For the power wire, an 8awg cable should have around a 60A fuse. 4awg I stick with 80A, but the wire has ampacity for more current. 80A's are just easier to find.
I stand corrected. this fuse would be located close to the power source, not close to the amp, correct, the amp really is irrelevant in this case.

I was misled by to OP.
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Old 07-18-2009, 02:52 PM   #9
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the fuse should be no bigger than the sum of all fuses on that circuit. so if the only thing on the line is the amp then go with what the amp is rated at.
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Old 07-18-2009, 03:09 PM   #10
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Quote:
Originally Posted by montgomery_30824 View Post
the fuse should be no bigger than the sum of all fuses on that circuit. so if the only thing on the line is the amp then go with what the amp is rated at.
While this can serve as a good rule of thumb, it is not sufficient for proper fuse selection. If wire up 4 1000w amps on a 20' piece of 8 awg, you can easily have more fused capacity in the amps than the power wire can safely handle. This is a bit of an exaggeration, but the point remains. You should pick the fuse that properly protects your power wire. It is not meant to protect the components that are powered by the power wire.

That being said, having a fuse that is under the ampacity of the wire and no larger than the sum of the fuses on the circuit can put a good constraint on what to purchase.
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Old 07-18-2009, 03:26 PM   #11
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Quote:
Originally Posted by montgomery_30824 View Post
the fuse should be no bigger than the sum of all fuses on that circuit. so if the only thing on the line is the amp then go with what the amp is rated at.
This is correct. Why play with Fire -literally- if you don't have to??? The manufacture doesn't just pull an arbitrary amperage out of it's ass for fuses. The fuse provided will be plenty to provide the nescicary amount of current to power the device.
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Old 07-18-2009, 04:19 PM   #12
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Quote:
Originally Posted by TacoNut View Post
This is correct. Why play with Fire -literally- if you don't have to??? The manufacture doesn't just pull an arbitrary amperage out of it's ass for fuses. The fuse provided will be plenty to provide the nescicary amount of current to power the device.
You're not understanding the point.
The fuse is there to protect the wire, if the amplifier total current draw is more than that wire/fuse combo can handle, it's time to move to a larger wire. With a larger fuse.
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Old 07-18-2009, 04:24 PM   #13
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Quote:
Originally Posted by sooner07 View Post
While this can serve as a good rule of thumb, it is not sufficient for proper fuse selection. If wire up 4 1000w amps on a 20' piece of 8 awg, you can easily have more fused capacity in the amps than the power wire can safely handle. This is a bit of an exaggeration, but the point remains. You should pick the fuse that properly protects your power wire. It is not meant to protect the components that are powered by the power wire.

That being said, having a fuse that is under the ampacity of the wire and no larger than the sum of the fuses on the circuit can put a good constraint on what to purchase.
and this is where common sense comes into play. don't wire your amps up with too small a gauge of wire. and i am sure he's not running thousands of watts of power so I am sure that 8 AWG is plenty big enough for his purpose. so again, stay with the rated fuse for what you are running and not what the wire is rated for because that will, in most cases, be too large of a fuse to protect anything.
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Old 07-18-2009, 04:27 PM   #14
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Quote:
Originally Posted by montgomery_30824 View Post
and this is where common sense comes into play. don't wire your amps up with too small a gauge of wire. and i am sure he's not running thousands of watts of power so I am sure that 8 AWG is plenty big enough for his purpose. so again, stay with the rated fuse for what you are running and not what the wire is rated for because that will, in most cases, be too large of a fuse to protect anything.
The fuse is to protect the wire from shorting out, not the amp. The amp has it's own fuses to protect itself.
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Old 07-18-2009, 04:43 PM   #15
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ok. just leave my truck alone.
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Old 07-18-2009, 04:58 PM   #16
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Quote:
Originally Posted by montgomery_30824 View Post
and this is where common sense comes into play. don't wire your amps up with too small a gauge of wire. and i am sure he's not running thousands of watts of power so I am sure that 8 AWG is plenty big enough for his purpose. so again, stay with the rated fuse for what you are running and not what the wire is rated for because that will, in most cases, be too large of a fuse to protect anything.
Did you miss the sentence after what you bolded? It was an exaggeration of the point. But the point still remains valid. The inline fuse (which should be no farther than 18" from the battery) is there to protect the power wire. It is not meant to protect anything else.

If you have properly fused components that draw more power than the power cable can handle, or you have a short, the inline fuse will go before the wire gets so hot that it catches things on fire. The maximum size for the inline fuse should be based on the ampacity of the wire, not what is drawing power from it. The minimum size for that fuse can, and wisely, is based on the total current draw of the components drawing power from that wire.

Common sense should say that you want power cable that is safely capable of carrying the amprage draw from the amps or what ever you are powering with it. The part of that safety is a fuse that is below the ampacity of the wire.
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Old 07-18-2009, 05:06 PM   #18
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Quote:
Originally Posted by johnecon2001 View Post
Don't worry. I don't do installations for a living anymore
I can see why. Who would want a properly fused vehicle anyway?
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Old 07-18-2009, 05:12 PM   #20
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johnecon, and sooner are 100% correct here, and frankly, I can't see why anyone would be arguing with their statements.

This is about as basic as it gets, and if you cant understand the fundamentals, you probably should not be installing your own audio equipment.
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