# fusing debate



## bobditts (Jul 19, 2006)

Scenerio:

amps in the trunk, battery under the hood. A single properly fused 4ga power wire run from the batt to the trunk to a non-fused distro block. 3 8ga runs from the distro to 3 amps and a small wire to the processor (we will say 18ga) approximately 4ft in length each. 

Question: do you.....

A: fuse the 4 wires after the distro block even though the 4ga wire is properly fused at the battery?

or

B: forget about adding extra fuses - the short wires are protected by the main fuse at the battery?

What is your answer and WHY?


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## kimokalihi (May 27, 2007)

I don't know a whole lot about electricity but I'm guessing you should fuse the invividual 8gauge wires just in case one of them happens to draw more current than it can handle but not enough to blow the fuse for the 4gauge because it's rated higher since the 4gauge wire can handle more power. 

I would never have thought about that if I was doing this setup had you not brought it up.

If all the wires were the same gauge as the main power wire and it had the right fuse for that size wire, I wouldn't bother fusing the others.

Am I right or is there more to it that I don't see?


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## bobditts (Jul 19, 2006)

Thats the thing, I dont know if there is a 100% right or wrong answer. Im pretty sure there is a best answer but im just curious what everyone would do personally.


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## Thumper26 (Sep 23, 2005)

my understanding is you fuse any time the wire changes size. so get a fused distro block for each of the extra wires. on the processor, you might need to get another fuse block to get it covered, or just run an inline fuse with it.


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## kimokalihi (May 27, 2007)

Yeah I'd definately fuse the processor, nothing like losing your H701. I wish I could even afford to buy one in the first place...God knows I can't afford to lose one due to laziness.


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## Infinity (Jun 28, 2005)

By most standards, you SHOULD fuse the individual 8's, but I never do. Actually, I've never blown a fuse on my power lines (knock on wood).


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## Rudeboy (Oct 16, 2005)

I may be missing something, but unless the fuse at the battery is sized for 8 AWG, say 50 AMPS, you have to fuse at the distro block or just after it. Doing it that way would make the use of 4 AWG pointless. Otherwise, as kimokalihi said, the fuse at the battery protects the 4 AWG up to the distro block, but the 8 AWG may fail before the fuse at the battery blows.


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## Oliver (Jun 25, 2007)

The fuse is to protect the wire...

Yes, if you understand the BCAE site, you will enjoy listening to your music, instead of posting rather funny situations that have happened to you .

The fuses in my friends amplifier did there job perfectly, he was listening to some strong bass oriented music...when he turned the volume knob up...both fuses blew as the inrush of current hit them [ 9002 Orion amplifier, A/B for his AA, Avalanche 12 " ].


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## flapperdink (Aug 27, 2007)

Fusing the individual 8 gauge wire runs should better protect the individual components. Say if you don't fuse the individual runs and only rely on the hood fuse (which may be around 100A or so) then if an amp on the 8 gauge run starts to short, that amp will have to draw 100A worth of current before the hood fuse blows. 

This could damage the unit beyond repair, and it could also cause a fire because the 8AWG wire is not designed to handle that much current draw.

IMO there's no hurt in adding the extra fuse. It may also help in isolating the faulty equipment if one of the components causes the whole system to come to a halt.

just my two cents worth of EE knowledge


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## Oliver (Jun 25, 2007)

This way will save you a little money and a little time [ as long as nothing goes wrong ]


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## durwood (Mar 7, 2007)

If the amps have fuses built in, then I wouldn't worry about it, however if there are no fuses to protect the amps I would definitely use one.

Fuse at the battery is to protect your battery and car from fires.

Fuses at the distro in the trunk are there to protect your amps if no internal fuses.

Lets say two amps connected (no internal fuses), no distro fusing. Amp one starts to fail, and it uses 30A safely but your fuse at the battery is 150A for the entire system. If that amp goes into meltdown, by the time that 150A fuses pops, that amp that usually draws 30A will be toast.

I use fused distros for easy service if anything in my system goes south. Alot easier to pop the cover and replace the same type of fuse for everything then to have to have all sorts of different types of fuses laying around.


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## kyheng (Jan 31, 2007)

Advantages of not adding fuse :
reduce restrictions of current flow(can we feel it? Atleast I cannot)
save money, of course. If your system requires 5 fuses and those fuses cost XX, then it will be 5XX.
Disadvantages :
Can result of fire(worst case)
If it don't burn your whole car out, atleast it will burn your money(amps, E-crossovers)


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## Oliver (Jun 25, 2007)

My nephew saw two guys jump out of their vehicle at a stoplight, open the rear doors and smoke poured out, they then began ripping wires out of their vehicle.

You guessed it, the wire was overfused, as the current went thru the wire, it began to melt the insulating on the wire.


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## quality_sound (Dec 25, 2005)

As long as there are fuses in the amps or processors and the fuse at the battery is the correct size then there's no reason for the extra fusing at the distro block.


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## Thumper26 (Sep 23, 2005)

while i agree that you're fine if the amps are fused, personally, i don't want a surge to get far enough in the chain to pop the fuses on the amps. just my .02


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## chad (Jun 30, 2005)

I sure love running one amp 

I'd fuse the processor close to the distro block and screw the short 8GA chunks ON AN AVERAGE SYSTEM, say 100A fuse at the battery. But I don't fuse at the battery for the max possible handling of the main line going back, I'm VERY conservative. My 4GA is fused now at 40A


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## unpredictableacts (Aug 16, 2006)

I would fuse the main wiring going to the trunk in the trunk before the distro block...to me it is more so convience...i like to disable my amplifiers from the rear if i am moving thing around or changing things up.


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## chad (Jun 30, 2005)

unpredictableacts said:


> ...i like to disable my amplifiers from the rear if i am moving thing around or changing things up.


I heard that's not the only thing you disable from the rear while "changing things up"


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## Thumper26 (Sep 23, 2005)




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## johnson (May 1, 2007)

I always used a fused distribution block when going to a smaller gauge even if there are already fuses inside the amp.


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## unpredictableacts (Aug 16, 2006)

chad said:


> I heard that's not the only thing you disable from the rear while "changing things up"


LOL....you got me.....I just off of work and my mind is not on gaurd........
+1 Chad


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## Oliver (Jun 25, 2007)

LMAO, sweet, Chad


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## JasonPaul (Jul 2, 2007)

durwood said:


> If the amps have fuses built in, then I wouldn't worry about it, however if there are no fuses to protect the amps I would definitely use one.
> 
> Fuse at the battery is to protect your battery and car from fires.
> 
> ...


X2
Protect your investment..


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## Mr Marv (Aug 19, 2005)

quality_sound said:


> As long as there are fuses in the amps or processors and the fuse at the battery is the correct size then there's no reason for the extra fusing at the distro block.



Something that appears to have been missed in this thread is the fact that the _short_ 8AWG from the distro block to the amp will have _more capacity_ than the _long_ 4AWG from the battery to the distro block and will be protected by the _proper_ fuse at the battery.


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## HIS4 (Oct 6, 2005)

The fuses on the power lines are typically not meant to protect your equipment, it's meant to protect the wire. Your equipment usually has built in fuses to protect itself from a fault condition. The reason for the inline fuse is to protect the wire from an overcurrent condition. If you change wire sizes and the smaller wire is not rated for the current allowed by the main fuse, then you should fuse the smaller wire with the appropriate sized fuse. For example if your 4 AWG is has a 100A fuse and then you hit a distribution block that splits to 3-8AWG and a 12 AWG then you should have a fuse for the maximum rated capacity of the smaller wires on each of the wires. I would probably put a 50A fuse on each 8 AWG and a 20A fuse on the 12 AWG to protect those wires from melting in the case of an overcurrent condition. If there were no fuses after the distribution block, you could possibly force 100A through the 8 AWG and 12 AWG wires which would melt the insulation off and possibly start a fire.


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## chad (Jun 30, 2005)

Mr Marv said:


> Something that appears to have been missed in this thread is the fact that the _short_ 8AWG from the distro block to the amp will have _more capacity_ than the _long_ 4AWG from the battery to the distro block and will be protected by the _proper_ fuse at the battery.


Egg-Zachary, some people forget that they have ever looked inside a fuse


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## Whiterabbit (May 26, 2006)

bobditts said:


> Thats the thing, I dont know if there is a 100% right or wrong answer. Im pretty sure there is a best answer but im just curious what everyone would do personally.


There is a 100% right answer. That answer is this:

For Safety, every connection point is a possible failure. Assuming you have a failure and the wire slips and grazes the frame, is there a fuse that protects the wire from burning? The wire under the hood may protect the 4 gauge, but if your non-fused D-block has a 16 gauge output, the 200 amp fuse isnt gonna do much to keep it from burning!

can you find ONE wire in the car that will burn if it slips and falls out of its place?

Need to add a fuse there.


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## Mr Marv (Aug 19, 2005)

Whiterabbit said:


> There is a 100% right answer. That answer is this:
> 
> For Safety, every connection point is a possible failure. Assuming you have a failure and the wire slips and grazes the frame, is there a fuse that protects the wire from burning? The wire under the hood may protect the 4 gauge, but if your non-fused D-block has a 16 gauge output, the 200 amp fuse isnt gonna do much to keep it from burning!
> 
> ...


Very good points.


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## Oliver (Jun 25, 2007)

A fuse or circuit breaker will protect what comes after it [ think up , {meaning before } and { down, meaning after }.

For example:

If the main breaker in your fuse panel trips, no more power to house.

Will this protect the transformer on the pole? { before the circuit breaker }


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## chad (Jun 30, 2005)

Hic said:


> Will this protect the transformer on the pole? { before the circuit breaker }


Depends on what else is on that transformer, if it's cooking along with you and your neighbors on it, and you dump a 200A short across it then yes, the main breaker in your home will protect it to a degree


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## Oliver (Jun 25, 2007)

Chad, you're not helping  

Hang on Consumers is here to reset my circuit breaker, the city just lost power, when my microwave and refrigerator were trying to run simultaneously on the same receptacle


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## chad (Jun 30, 2005)

Hic said:


> Chad, you're not helping


I was being a smartass, sorry


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## bobditts (Jul 19, 2006)

Thanks for all of the input guys. I kinda figured what the responses I would get but I just wanted to make sure. This is great info for members in the future. It seems the popular concesus is to fuse at the battery and at or right after the distro block.


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## Oliver (Jun 25, 2007)

chad said:


> I was being a smartass, sorry


So was eye, lovin every minute of it  

I think some should hop on over to [ Basics of Car Audio and Electronics ]!

Some fo hist is scary, some ton


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## khail19 (Oct 27, 2006)

My rule of thumb is fuse at the battery, and every time the wire steps down in size.


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## Oliver (Jun 25, 2007)

There is nothing that will be done, where safety is not first and foremost !


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## GlasSman (Nov 14, 2006)

kimokalihi said:


> Yeah I'd definately fuse the processor, nothing like losing your H701. I wish I could even afford to buy one in the first place...God knows I can't afford to lose one due to laziness.


The H700/H701 has a white twisty inline mini AGU fuse from the factory on the yellow wire.

And yes...if theres a reduction in wire gauge you fuse.


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## Oliver (Jun 25, 2007)

Chad, this is probably a good time to mention-The safety on your gun will prevent you from accidently discharging the firearm


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## Mr Marv (Aug 19, 2005)

Just to be more clear, reduction in wire _*capacity*_ is the determining factor in whether or not you _*need*_ to fuse that wire not just wire size _(capacity_ is determined by the _size *and* length_ of the wire).


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## Vestax (Aug 16, 2005)

khail19 said:


> My rule of thumb is fuse at the battery, and every time the wire steps down in size.


Definitely my rule of thumb as well. This should've been the answer the first time. There is a reason why you have one or two fuse boxes in your car.


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## bass_lover1 (Dec 10, 2005)

I've always believed that the fuse protects the wire from a dead short, nothing else.

In my setup, I've got 0awg running off the battery, with a 150A ANL fuse, back to my trunk. There I have an unfused distro block that splits 4awg out to my 3 amps. The runs are each less than 3ft and they do not touch any sharp panels or objects that could cause them to short. I leave them unfused, for that reason, if they manage to short out in my car, it'll be because some act of God. Could they short out? Yes, but it's HIGHLY unlikely, because they haven't in the 3.5 years my setup has been installed like this.

I did however, blow the 40A fuse when my LP 2.2 was powering a single Dayton HO 12. I decided to ditch the fuse, because the power line is like 8-10 inches, and never touches anything metal.


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## HIS4 (Oct 6, 2005)

Mr Marv said:


> Just to be more clear, reduction in wire _*capacity*_ is the determining factor in whether or not you _*need*_ to fuse that wire not just wire size _(capacity_ is determined by the _size *and* length_ of the wire).


I'm going to have to disagree with you on this one. Current carrying capacity is not affected by length but voltage drop is. Voltage drop is affected by length because the impedence of the wire increases as a function of length. If you're trying to keep the voltage within a certain range, then yes, you increase the size of the wire to carry a specified current in order to limit the voltage drop.


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## Mr Marv (Aug 19, 2005)

HIS4 said:


> I'm going to have to disagree with you on this one. Current carrying capacity is not affected by length but voltage drop is. Voltage drop is affected by length because the impedence of the wire increases as a function of length. If you're trying to keep the voltage within a certain range, then yes, you increase the size of the wire to carry a specified current in order to limit the voltage drop.


That's cool!  I'm no EE for sure and that info was from a well respected EE I speak to quite often about stuff like this however I'll be the first to admit that with the overload on my brain I could have it wrong!


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## chad (Jun 30, 2005)

Mr Marv said:


> That's cool!  I'm no EE for sure and that info was from a well respected EE I speak to quite often about stuff like this however I'll be the first to admit that with the overload on my brain I could have it wrong!


Regardless, a 3' hunk of 8 guage can carry a hell of a lot of current before melting! The starter primary on my car is 8 Ga!


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## Mr Marv (Aug 19, 2005)

chad said:


> Regardless, a 3' hunk of 8 guage can carry a hell of a lot of current before melting! The starter primary on my car is 8 Ga!


That's how I understood it.


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## HIS4 (Oct 6, 2005)

The insulation on the wire will not melt on a large transient draw which is what is common in car audio. The wire can handle short burst of current higher than its rated capacity but if the current draw is sustained for a longer duration, the heat will build up and eventually melt the insulation.


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## chad (Jun 30, 2005)

HIS4 said:


> The insulation on the wire will not melt on a large transient draw which is what is common in car audio. The wire can handle short burst of current higher than its rated capacity but if the current draw is sustained for a longer duration, the heat will build up and eventually melt the insulation.


Then the question that needs to be answered is how much current can a short chunk of 8GA sustain and for how long. I wouild feel comfortable allowing a peice of 8GA to blow a 100A-150A fuse. It WILL pass that current long enough to not heat up and still crack the fuse. Just like it does it in your starter wire. A short is a transient


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## HIS4 (Oct 6, 2005)

chad said:


> Then the question that needs to be answered is how much current can a short chunk of 8GA sustain and for how long. I wouild feel comfortable allowing a peice of 8GA to blow a 100A-150A fuse. It WILL pass that current long enough to not heat up and still crack the fuse. Just like it does it in your starter wire. A short is a transient


There are many variable involved with that calculation. It is not uncommon to see undersized wire in a motor starting application.

For example, in a/c installations, the motor for the a/c consendser will have a certain running load. Per electrical code, the conductor feeding that load is required to be sized for 125% of that running load. The motor also has another rating for the current drawn when the motor is started from is locked rotor state which is typically when the motor is first started. It is not uncommon to see a locked rotor current rating that is about 5-6x that of the running load. So you have a transient draw of 5-6x the running load delivered over a conductor rated for only 125% of the running load. To make it even more confusing, electrical code requires that the circuit breaker protecting the conductor is sized for between 175% and 225% of the running load.


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## chad (Jun 30, 2005)

HIS4 said:


> There are many variable involved with that calculation. It is not uncommon to see undersized wire in a motor starting application.
> 
> For example, in a/c installations, the motor for the a/c consendser will have a certain running load. Per electrical code, the conductor feeding that load is required to be sized for 125% of that running load. The motor also has another rating for the current drawn when the motor is started from is locked rotor state which is typically when the motor is first started. It is not uncommon to see a locked rotor current rating that is about 5-6x that of the running load. So you have a transient draw of 5-6x the running load delivered over a conductor rated for only 125% of the running load. To make it even more confusing, electrical code requires that the circuit breaker protecting the conductor is sized for between 175% and 225% of the running load.


Or the use of motor start breakers, which, incidentally us audio guys LOVE


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## Rudeboy (Oct 16, 2005)

chad said:


> Then the question that needs to be answered is how much current can a short chunk of 8GA sustain and for how long.


Or it doesn't even have to be considered if you put a fuse on it. This is an interesting theoretical discussion and some people may be able and willing to do the calculations to know they are safe. The rest of us should just fuse for the wire every time we step it down in size. 

Fusing should be the rule of thumb, not fusing should be the exception. To those who are thinking otherwise, Chad did not just say that you don't have to fuse anywhere but at the battery. You know who you are


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## chad (Jun 30, 2005)

Rudeboy said:


> Or it doesn't even have to be considered if you put a fuse on it. This is an interesting theoretical discussion and some people may be able and willing to do the calculations to know they are safe. The rest of us should just fuse for the wire every time we step it down in size.
> 
> Fusing should be the rule of thumb, not fusing should be the exception. To those who are thinking otherwise, Chad did not just say that you don't have to fuse anywhere but at the battery. You know who you are


Again, Think god I run just one amp  One fuse at the battery sized for the amplifier and the small 12Ga tap off of that fused at a blazing 1A for the fans 

Chad


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## MarkZ (Dec 5, 2005)

I haven't read the entire thread, so I don't know if this was brought up. But I think it can sometimes be useful to fuse your remote wire too. Not to protect the wire, but to protect the head unit's remote output. You'll see some head units with an inline fuse already on the remote wire.


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## Mr Marv (Aug 19, 2005)

HIS4 said:


> I'm going to have to disagree with you on this one. Current carrying capacity is not affected by length but voltage drop is. Voltage drop is affected by length because the impedence of the wire increases as a function of length. If you're trying to keep the voltage within a certain range, then yes, you increase the size of the wire to carry a specified current in order to limit the voltage drop.


I found where my brain overload came from. :blush: The scenario I was speaking of to the EE had a 4 awg power wire already installed and I reduced it to 8awg at a distro block in order to physically fit in the amp (30 amp draw). Since this was the _only_ load connected to the wire(s) I was told a fuse at the reduction point was not *necessary* _as long as the fuse at the battery was rated lower than the capacity of the *smallest* wire_.


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## Abmolech (Nov 2, 2006)

A fuse is a heat limiting device.

As long as it can limit the heat to stop the device from reaching ignition temperature it has done its job.

The fuse at the battery is to protect YOU.
The fuses at the power amplifier are to protect the manufacturer from liable. By the time the fuses have limited the heat in a power amplifier, sufficient damage has occurred to the unit. They are there to stop fire only.


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## HIS4 (Oct 6, 2005)

Mr Marv said:


> I found where my brain overload came from. :blush: The scenario I was speaking of to the EE had a 4 awg power wire already installed and I reduced it to 8awg at a distro block in order to physically fit in the amp (30 amp draw). Since this was the _only_ load connected to the wire(s) I was told a fuse at the reduction point was not *necessary* _as long as the fuse at the battery was rated lower than the capacity of the *smallest* wire_.


That would be correct. Since the fuse is sized for the smallest wire in the run, both wires are protected. Basically you just have a section of oversized wire which will help reduce voltage drop if nothing else.


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## Oliver (Jun 25, 2007)

MarkZ said:


> I haven't read the entire thread, so I don't know if this was brought up. But I think it can sometimes be useful to fuse your remote wire too. Not to protect the wire, but to protect the head unit's remote output. You'll see some head units with an inline fuse already on the remote wire.


Yes !
Ideally, if you run the remote wire to a relay and then the relay sends power to the amps, this protects the HU from taking a direct hit if the amps fail or otherwise get too much current flowing thru the wires.

To rephrase this if the remote goes to an amp=then the amp can get to the source.

Anyone who has experienced this, sends the HU in for repairs.

A relay will protect your HU from costly shipping and repairs


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## MarkZ (Dec 5, 2005)

Hic said:


> Yes !
> Ideally, if you run the remote wire to a relay and then the relay sends power to the amps, this protects the HU from taking a direct hit if the amps fail or otherwise get too much current flowing thru the wires.
> 
> To rephrase this if the remote goes to an amp=then the amp can get to the source.
> ...


I'm not big on the relay idea though, because I think you need to use an ungodly number of devices until you start taxing the remote output. Also, I'm not the biggest fan in the world of using a relay as a fuse, because you've always got the possibility (albeit small) of somehow shorting the relay coil -- whether it's by shorting it to the ground in close proximity to the relay pin, or by somehow destroying the relay itself. Also, not all relays have quenching diodes installed. Bosche ones usually do, but there are some relays that don't...


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## Oliver (Jun 25, 2007)

1] fuse block - wire - relay - amp [ this is a power circuit from your fuse panel to your amps ].

2] HU remote out - wire - relay [ this becomes a control circuit, that engages a power circuit ].


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## Ge0 (Jul 23, 2007)

Forgive me for being too lazy to read through the entire post. But, just in case this has not already been brought up.

Install fuses to keep each individual wire within its safe operating limits should a fault occur. If you have a fuse right at the battery this should be sized to protect the main power cable running to the back of your vehicle. And yes, this fuse should be as close to the battery as possible. Preferably right on top of the damn battery terminal. Now, if you have a distro block branching off of this feeding other components (example, two 8ga conductors for amps and a couple 18ga conductors for processors) FUSE EACH INDIVIDUALLY according to the wires rating. This should happen at, or as close as possible, to the distro block. Nevermind the fact that your amps and processors may have built in fuses.

If an amp or processor takes a crap internally then the fuse built into that device will protect the wiring (that is if that equipment has a built in fuse). HOWEVER, what happens if the cable leading to the amp or processor gets abraided and shorts to ground (chassis) somewhere between the distro block and amp/processor? Without fuses at the distro block you only have the fuse at the battery to help you. Do you really want 200+ amperes flowing through an 18ga cable? Hell, that's dangerous for a 8ga cable. They WILL catch fire before that fuse blows.

The fuse at the amp/processor won't help. Since the short occured before this, no current flows through the fuse built into the amp/processor.

I know a lot of you are super anal about how you route wiring and also put pretty jacketing over it to protect it. But, **** happens. What happens if you get in an accident and a piece of sheet metal cuts through a wire? If you car wasn't damaged too bad, it will be if you didn't fuse you stuff properly. It could also turn into a crispy critter. I've seen some pretty stupid stuff (hell, I've done some pretty stupid stuff) in my time. Don't take the risk. Say you drive a screw through a power wire and into the chassis by accident... Why do you think all household wiring is fused (or breakered) right at a distrobution panel? Why not fuse them at each outlet (equivalent to fuses inside an amp)? For the exact reasons I mentioned above...

Adding fuses is like buying insurance. Chances are you'll never need it. But, you'll be glad you had it when you do need it. Don't be cheap and save yourself the $10 to $20 it would take to buy a simple fused distro block. Spend the money and have some piece of mind.

Ge0


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## Ge0 (Jul 23, 2007)

Hic said:


> Yes !
> Ideally, if you run the remote wire to a relay and then the relay sends power to the amps, this protects the HU from taking a direct hit if the amps fail or otherwise get too much current flowing thru the wires.
> 
> To rephrase this if the remote goes to an amp=then the amp can get to the source.
> ...


Make damn sure you suppress the inductive kickback a relay coil will give you if connecting a relay to a remote output. The inductive voltage spike WILL kill the device inside the head unit. All it takes is a $0.20 diode available at Radio Shack. Well, maybe a $2.00 diode if purchased at radio shack .

Ge0


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## Whiterabbit (May 26, 2006)

for all future reponses, please read the entire thread. It will help prevent the thread getting much larger.

thanks,


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## Megalomaniac (Feb 12, 2007)

durwood said:


> If the amps have fuses built in, then I wouldn't worry about it, however if there are no fuses to protect the amps I would definitely use one.
> 
> Fuse at the battery is to protect your battery and car from fires.
> 
> ...


a fuse on wire is to protect the wire from catching fire....

edit: i try to fuse all my wires. it helps me sleep better at night knowing i a fuse a to protect my equipment for the most part


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## MiloX (May 22, 2005)

Vestax said:


> Definitely my rule of thumb as well. This should've been the answer the first time. There is a reason why you have one or two fuse boxes in your car.


Mine 2.

Wire gets step-downed? Wire gets a fuse.


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## MarkZ (Dec 5, 2005)

MiloX said:


> Mine 2.
> 
> Wire gets step-downed? Wire gets a fuse.


I never really saw the point of this, actually. And Marv hit on the reason earlier.

The difference between, say, 4ga into a block and 8ga coming out is so minor that you should just fuse the 4ga as if it was an 8ga. You're not going to be pushing the limits of the wire anyway, so fusing the 4ga for lower current will be perfectly fine and will protect both wires with one fuse. The only time I ever put a new fuse is when I step down in a ridiculous step, like 4ga to 18ga (yes, my distro block has one 18ga wire coming out of it).


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## durwood (Mar 7, 2007)

Megalomaniac said:


> a fuse on wire is to protect the _anything_ from catching fire....


fixed.


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## HIS4 (Oct 6, 2005)

MarkZ said:


> I never really saw the point of this, actually. And Marv hit on the reason earlier.
> 
> The difference between, say, 4ga into a block and 8ga coming out is so minor that you should just fuse the 4ga as if it was an 8ga. You're not going to be pushing the limits of the wire anyway, so fusing the 4ga for lower current will be perfectly fine and will protect both wires with one fuse. The only time I ever put a new fuse is when I step down in a ridiculous step, like 4ga to 18ga (yes, my distro block has one 18ga wire coming out of it).


4 AWG has almost twice the current carrying capacity of 8 AWG so I would not call that a minor step down but if you're load is small enough to be supported by the 8 AWG then yes, you can fuse the 4 AWG for the 8 AWG capacity and be fine. 

In this case though we're talking about multiple 8 AWG feeds coming off a single 4 AWG main so fuses should be installed at each 8 AWG because there's a chance you would blow the main fuse if it was only sized for the capacity of a single 8 AWG.


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## MarkZ (Dec 5, 2005)

HIS4 said:


> 4 AWG has almost twice the current carrying capacity of 8 AWG so I would not call that a minor step down but if you're load is small enough to be supported by the 8 AWG then yes, you can fuse the 4 AWG for the 8 AWG capacity and be fine.


I meant that it's minor in the sense that we don't need to fuse the 4ga wire according to the max that 4 ga. can handle because we're not operating these wires at their limits. Most of the time, we're choosing wire based on the minimum acceptable voltage drop. So, typically, those of us who use 4ga wire could get away with using 10ga wire before safety starts to become a concern. But we don't because the voltage drop associated with a 10ga. wire is unacceptable to us. So if we fuse the 4ga. as if it was an 8ga., then we won't pop the fuse under normal usage.



> In this case though we're talking about multiple 8 AWG feeds coming off a single 4 AWG main so fuses should be installed at each 8 AWG because there's a chance you would blow the main fuse if it was only sized for the capacity of a single 8 AWG.


If the main fuse was fused as an 8ga., then the other fuses would be unnecessary. Doesn't matter how many of them there are.


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## Hi There (Mar 16, 2007)

Most issues that would cause one to have to lean on the fuse, imho, have nothing to do with the rated capacity of the wire. 

I think, in our assessment of how to fuse, we should be asking ourselves, "In what situations are fuses typically needed?" Most of these situations involve abrasion of the wire, or some instance where the wire becomes partially connected to ground. This connection can be any size or shape from a sharp abrasion to a few strands connecting to ground to an open wire end making a fairly full contact. In all these situations, you have some amount of localized heating at the point of contact to ground, unless you just so happen to make complete and full contact of the wire to the vehicle chassis or other source of ground potential. 

So, we should balance the design of our protective devices against the safety concern of some amount of localized heating in a fault causing a fire. 

We have no way to be 100% safe, in any regard, from generating enough heat to cause a fire, regardless of the wire size in question. In a fault situation, it's usually not a question of wire gauge and current carrying capacity of a properly connected wire. So, in the case of utilizing wire with various points of distribution and size change, what exactly is wrong with fusing at wire size changes? It seems to me a good compromise of safety versus usability, although it has little to do with overcoming the capacity of the wire. I think it would have more to do with partial faults to ground not being enough to blow large size fuses at the head end, but enough to cause localized heating that is dangerous in a smaller wire.


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## Megalomaniac (Feb 12, 2007)

durwood said:


> fixed.


quit being so ****


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## Rudeboy (Oct 16, 2005)

A few other things to consider if you choose to step down wire size without fusing at the point of transition. If you fuse at the battery for the smaller gauge wires you are assuming that nobody will ever look under the hood and say: "what idiot put a 50 AMP fuse on 4 AWG" ? before replacing it with a 125. I can absolutely imagine myself doing that.

Many of us run power for the system we want to have rather than the one we are actually installing. I've got 1/0 running from the battery to the trunk and know without any doubt that 4 AWG would more than meet my needs. I can fuse for my existing requirements but if I upgrade, I'm again counting on myself to remember that I didn't fuse for the wire originally. 

If you follow standards, it' much less likely that you or somebody else will do something dangerous that seems logical at that moment.


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## quality_sound (Dec 25, 2005)

I remember reading an article a looooooong time ago that you size your main fuse at half the reserve capacity rating of your battery. 

Thoughts?


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## Oliver (Jun 25, 2007)

quality_sound said:


> I remember reading an article a looooooong time ago that you size your main fuse at half the reserve capacity rating of your battery.
> 
> Thoughts?


Go here : http://www.bcae1.com/

# 14 {Fuses}


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## Diru (May 23, 2006)

Less then a paycheck for proper fusing, or thousand of dollars to replace it all cause the insurance company won't, because you added **** that was not from the factory. 

No debate, fuse it or loose it, any questions?


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## Oliver (Jun 25, 2007)

Diru said:


>


That is the "Hottest" car, I've seen in awhile


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## tr0y_audi0 (Feb 13, 2007)

Rudeboy said:


> I may be missing something, but unless the fuse at the battery is sized for 8 AWG, say 50 AMPS, you have to fuse at the distro block or just after it. Doing it that way would make the use of 4 AWG pointless. Otherwise, as kimokalihi said, the fuse at the battery protects the 4 AWG up to the distro block, but the 8 AWG may fail before the fuse at the battery blows.



I have always felt the same way, I always use a fused distro block
For only afew bucks more why not...


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## HIS4 (Oct 6, 2005)

MarkZ said:


> If the main fuse was fused as an 8ga., then the other fuses would be unnecessary. Doesn't matter how many of them there are.


You wouldn't need to worry about protecting the wire but load may become an issue. I don't know what the loads are at the end of those 8 AWG wires but I would think that you may approach the limit of the wire if you're combining 3 of those loads on one 8 AWG.


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## MarkZ (Dec 5, 2005)

HIS4 said:


> You wouldn't need to worry about protecting the wire but load may become an issue. I don't know what the loads are at the end of those 8 AWG wires but I would think that you may approach the limit of the wire if you're combining 3 of those loads on one 8 AWG.


I understand, but I think you would need a lot more than 3 branches for that to become a problem. Again, remember that we're not operating these devices anywhere near the current capacity of the wires. You would probably have a hard time heating up a 16ga wire with a 500w amp at full blast, let alone an 8ga wire with three of them. 

Also keep in mind that the musical transients aren't typically long enough in duration to pop the fuse, so unless you're playing sine waves your average current draw is going to be considerably lower.


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## HIS4 (Oct 6, 2005)

MarkZ said:


> I understand, but I think you would need a lot more than 3 branches for that to become a problem. Again, remember that we're not operating these devices anywhere near the current capacity of the wires. You would probably have a hard time heating up a 16ga wire with a 500w amp at full blast, let alone an 8ga wire with three of them.
> 
> Also keep in mind that the musical transients aren't typically long enough in duration to pop the fuse, so unless you're playing sine waves your average current draw is going to be considerably lower.


That's true. The chances of having a large transient draw from all three at the same time is small. The circuit breaker near my battery is very undersized for the cable I'm running. I have a 150A breaker on the main 1/0 wire which branches off to 2-4AWG with 100A breakers on them. The 100A breakers are recommended by the amp manufacturer because they have no internal fuses. The manufacturer actually recommends 125A but I felt that the 100A would be sufficient.


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## MiloX (May 22, 2005)

So consider the source on this... You all know how I am with wiring....

I am amazed that there is even a debate on this. 

The fuse protects the wire. If you drop the wire size... Fuse it.

Simple. IMO, of course.


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## Tommythecat (Apr 6, 2006)

I would say that no one has mentioned the problems that might arise when your battery gets shorted out and how IT might feel instead of just the wire.

It's important if you're running a battery under the hood and 1(+) in the trunk to fuse at the front and the back batteries for all of their safeties. If one of those was missing and the wire was shorted in the middle, it could go badly for a battery.


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## Oliver (Jun 25, 2007)

OK,

We need a consensus of opinion...

A fuse protects ______ ?

a] the wire
b] the battery
c] the alternator
d] the amplifier
e] anything electrical within 5 feet of it
f] They're really just for looks
g] I only use circuit breakers
h] Beats the hell out of me

BCAE, has some reading on this.


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## MarkZ (Dec 5, 2005)

Hic said:


> OK,
> 
> We need a consensus of opinion...
> 
> ...


i] the stuff downstream from the fuse.


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## Daishi (Apr 18, 2006)

Fuses protect the wire IMO. I wouldn't want an 8 awg wire fused upstream only with 130A fuse for a 4 awg wire...


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## Sassmastersq (Jan 12, 2007)

The fuse only protects downstream from it, however, if the install is proper, and the wire can't short out, then it will also protect the wire ahead of the fuse. Ideally there should be a fuse coming right off of the battery terminal to protect the battery and the wire.


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## Oliver (Jun 25, 2007)

along the same lines...

How are fuses rated _____ ?

1] by amperes { in current }
2] by voltage { in electromotive force}
3] by ohms { in resistance }
4] by the color of the fuse

How is wire size rated _____ ?

1] by the load in amperes it can safely handle
2] by the amount of electromotive force the insulation can contain safely
3] by the color of the insulation on the wire


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## Tommythecat (Apr 6, 2006)

You are a total _________ ?
a) Fool to ignore reality
b) Sheep to only take one website as fact
c) Savior
d) Master of asking loaded quiz questions


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## kyheng (Jan 31, 2007)

After 9 pages, this thread still ongoing, with some facts keep on repeating and repeating. I will suggest to close this thread, else it might turn >50pages of debating the same thing....


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## Oliver (Jun 25, 2007)

Tommythecat said:


> You are a total _________ ?
> a) Fool to ignore reality
> b) Sheep to only take one website as fact
> c) Savior
> d) Master of asking loaded quiz questions


Know enough to be dangerous , electricians apprentice for 1/2 a year, studied electricity in college [ instructor, told me to go home during final ! He said what is the point since you got a 100 on everything already ]

HVAC Technician [ graduated 35th in the graduating class [ for whole college ]of over 6,000 .

Still trying to remember lefty lucy , righty tighty [ with Chads help  ]

Truly believe in this instance [ fuse is to protect the wire ].

You are a total ?????? [ I can think of a few answers to this ], maybe, even the one your thinking of !


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## Tommythecat (Apr 6, 2006)

Sorry man, I was being a total dick. I didn't know you had such good grades in school...


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## Oliver (Jun 25, 2007)

A fuse let's you know something is wrong, and protects your investment.

Whether or not you figure out the problem or just keep replacing the fuse is up to you .


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## Exalted512 (Jul 23, 2006)

Fuses are for pussies.
-Cody


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## Whiterabbit (May 26, 2006)

for all future reponses, please read the entire thread. It will help prevent the thread getting much larger.

thanks,


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## bobditts (Jul 19, 2006)

congrats!!!!! you guys have taken a perfectly good thread and turned it into a SDOT worthy worthless POS. I hope you are all happy you bickering whining pansies.  

**disclaimer - this statement was only directed at those involved in the immature cyber "fighting"**


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## quality_sound (Dec 25, 2005)

Sassmastersq said:


> The fuse only protects downstream from it, however, if the install is proper, and the wire can't short out, then it will also protect the wire ahead of the fuse. Ideally there should be a fuse coming right off of the battery terminal to protect the battery and the wire.


How would a fuse protect the wire UPSTREAM of it. If it shorts between the battery and the fuse sure the fuse will blow but it won't stop the flow of current.


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## MadMaxSE-L (Oct 19, 2006)

quality_sound said:


> How would a fuse protect the wire UPSTREAM of it. If it shorts between the battery and the fuse sure the fuse will blow but it won't stop the flow of current.


I think he was trying to say that if the fuse was close enough to the battery that if it blew it would prevent the rest of the wire upstream of it from contacting a ground. By install it seems like he meant keep the fuse as close to the batt. as possible...

that's how I took it at least.


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## Oliver (Jun 25, 2007)

quality_sound said:


> How would a fuse protect the wire UPSTREAM of it. If it shorts between the battery and the fuse sure the fuse will blow but it won't stop the flow of current.


Once the fuse blows, "All is good, it breaks the circuit"


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## quality_sound (Dec 25, 2005)

Hic said:


> Once the fuse blows, "All is good, it breaks the circuit"


Except for the length of wire between the terminal and the fuse.


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## Oliver (Jun 25, 2007)

Hot and sparky


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## quality_sound (Dec 25, 2005)

Hic said:


> Hot and sparky



Kinda like that burrito that catches fire in the Taco bell commercial.


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## MarkZ (Dec 5, 2005)

Hic said:


> along the same lines...
> 
> How are fuses rated _____ ?
> 
> ...


The colors aren't a quality of the wire or fuse though. The other stuff is.


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## HIS4 (Oct 6, 2005)

Hic said:


> Know enough to be dangerous , electricians apprentice for 1/2 a year, studied electricity in college [ instructor, told me to go home during final ! He said what is the point since you got a 100 on everything already ]
> 
> HVAC Technician [ graduated 35th in the graduating class [ for whole college ]of over 6,000 .
> 
> Truly believe in this instance [ fuse is to protect the wire ].


You need to study electricity more. Fuses are designed into a system to protect what is downstream from the fuse. Per NEC, all components should be rated for as much current as the upstream overcurrent device will allow.


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## Oliver (Jun 25, 2007)

HIS4 said:


> You need to study electricity more. Fuses are designed into a system to protect what is downstream from the fuse. Per NEC, all components should be rated for as much current as the upstream overcurrent device will allow.


Thank you !

I'll fuse my boss 2000 watt amp with a 15 amp fuse and run 14 guage to it!

Call me crazy


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## Fran82 (Jul 30, 2007)

Whiterabbit said:


> There is a 100% right answer. That answer is this:
> 
> For Safety, every connection point is a possible failure. Assuming you have a failure and the wire slips and grazes the frame, is there a fuse that protects the wire from burning? The wire under the hood may protect the 4 gauge, but if your non-fused D-block has a 16 gauge output, the 200 amp fuse isnt gonna do much to keep it from burning!
> *
> ...


Yes. Every wire that was installed at the factory.


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## Gary S (Dec 11, 2007)

Some of the excessive use of fuses is due to the popularity of car stereo soundoffs... the more thingys you have the more points you can score... even if they are unnecessary.


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## bobditts (Jul 19, 2006)

alright, who brought this thread back from the dead!  I thought this was all said and done with?


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## 89grand (Nov 23, 2006)

When threads get resurected from the dead, it's usually a sign that things are sort of slow on the forum.

If nothing new and exciting is going on, people look for old threads to comment on.


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## Whiterabbit (May 26, 2006)

Fran82 said:


> Yes. Every wire that was installed at the factory.


Those factories products are to be avoided. Honda is certainly not one of them. Not coming from the factory a fire trap.


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## Fran82 (Jul 30, 2007)

Whiterabbit said:


> Those factories products are to be avoided. Honda is certainly not one of them. Not coming from the factory a fire trap.


I've owned Hondas and many other brands of cars, and NONE of them that I know of has fusing at the front and back of the car. So when I fuse my system, there is just one fuse, under the hood. Each component is then fused, hopefully internally. That should be enough protection, otherwise every car on the road is in danger of going up in flames based on improper fusing.


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## Fran82 (Jul 30, 2007)

bobditts said:


> alright, who brought this thread back from the dead!  I thought this was all said and done with?


Sorry :blush:


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