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The easiest way without alot of math and guess work with efficency is too look at the fuses that come with the amp...That fuse tells you the max current that amp can draw before problems.

Add all the fuse values together and you have the max the amps can draw. So if for exapmle the 2000w amp has 2-80a fuses..and the 300w has a 30a fuse..190a would work but I would reccomend going slightly over in case of a surge..so a 200a would be fine. Remember the basics..if you use a fuse thats too small..it won't hurt anything..it will just blow when the current demands exceed it. If you use a fuse thats slightly larger..that also will not cause any problems in itself..the only thing that should blow the fuse is a short..or if the amp draws too much..now if the amp draws to much due to a defect..well no fuse will save the amp..it needs servicing or replacement regardless.

The main fuse is there for protection against wires or product burning up in the event of a short in the wire..or internal problem with the amp..it should not have an effect on it's performance.

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Too much effort...

How big is the cable you are installing. The fuse is there to protect THAT anyway (the cable and the car...), it has nothing whatsoever to do with protecting the amplifers. At the distro block, fuse according to the OUTPUT wire size.

#8 - fuse at 100A
#4 - fuse at 150A
#2 - fuse at 225A
1/0 - fuse at 350A

Any decent quality amplifier will have it's own protection fuses within or on it anyway. THOSE are for protecting the amplifier - period.

See here... Our wonderful 12v mods and admins have provided all of us with an awesome tool, specifically to answer this question.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Yes, looking at the total demand capability of your amplifiers and other parts of a system is one way to determine what size power and ground cable to use (and how large an alternator you are likely to need) but the fuse size is ALWAYS determined by the size of the power cable. The fuse used at the battery or at a distribution block is to protect the cable downstream, not the amp. Always fuse for the cable size. Always use no larger fuse than the smallest wire in the power chain before the next fuse and always use a new appropriately-sized fuse if the cable gauge is lowered.

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I have a basic question. with the statement "the fuse size is ALWAYS determined by the size of the power cable" wouldn't it be more appropriate to state "the size of the wire as well as the fuse rating is determined by the max current draw of the amp(s)"?

In other words..if the system called for a 4ga wire..and we used a zero gauge..is it understood that we should intentionally put in a larger fuse then required soley based on the wire gauge and not based on the systems maximum draw potential?

Someone enlighten me please.

I think I slightly misunderstand the post regardless as it states "there is a fuse in the block"..why would a distribution block have only 1 fuse?? He is asking about one fuse..anyone else notice that?

Oh and I hope no one read into my previous post thinking I meant the fuse protects the amp..not so, I only meant to state that the main fuse will protect the wire in the event of a short or excessive current draw...the amps protection fuse(s) are there to protect from the amp burning up in the event of an internal problem or short..not prevent it the problem, and should always be a lower rating then the main fuse. Hope I am understood.

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master5 wrote:

I have a basic question. with the statement "the fuse size is ALWAYS determined by the size of the power cable" wouldn't it be more appropriate to state "the size of the wire as well as the fuse rating is determined by the max current draw of the amp(s)"?

No, not in my opinion. The max draw of the amps can be used to determine how large a power and ground cable is required (like I stated in my previous post) but the fuse used in the power system is to protect the wire (and you) from over current.

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master5 wrote:

..if the system called for a 4ga wire..and we used a zero gauge..is it understood that we should intentionally put in a larger fuse then required soley based on the wire gauge and not based on the systems maximum draw potential?

The consideration of fuse value is based on the gauge of the wire it protects. If the fuse is NOT chosen with this consideration, other influences were allowed to interfere with the reasoning process.

Why use a fuse or breaker value of 300 to 350 amps on that 1/0 wire if the pull of the gear doesn't support such a large value? You have to answer this yourself with the simple question: Why is there a 1/0 wire installed when all that was needed was 4 gauge? That's an example of faulty reasoning based on the wrong consideration; it's based on the pull of the equipment, not the wire size. Or is it the associated cost of the fuse or breaker that prompts the choice in fuse value? There again, invalid reasoning. And how valid is that 1/0 wire anyway when you've installed a 4 ga. eqivalent fuse in the run? ...or with a breaker that will shut off when the thermal limits of a 4 ga. wire has been reached?

The intent here is to provide the basic principles of why and how. It should be known that the fuse protects the wire, and any mention of the current system's demand on the fuse's ability should not be addressed as it has no bearing on the principle of this wire/fuse safety system. A professionally-installed system should always have the correct safety devices in place for the wires they serve.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Ok thanks guys..I get the picture. The thing is in the real world where I am in the trenches performing all kinds of installs on a daily basis (not talking about a comp vehicle where there are rules and judging)..I might for example have some "kid off the street" come in to install all his "stuff".

Now lets say he has a generic 200watt amp and it has a 40a fuse from the manufacturer mounted on the amp. And he has a 4ga. wire long enough for the job. Now what I would do if he needed to buy a fuse from me is sell him a 50a or 60a fuse and be totally confident this will work.

If I go strictly by the logic above..I would want to use a 150a fuse..or sell him a smaller wire. Now I understand that a 4ga is overkill for this amp...but so would a 150a fuse, and the last thing I would do is reccomend a smaller wire..can you see my point as well? Just using common sense alone I have no "fear" of using a wire gauge that is larger then required..but I might have a concern with using a fuse that is 3 times the rating required to run this system..still keeping in mind it's sole purpose is to protect the wire/vehicle.

When I am designing a system myself from scratch....I determine the wire gauge based on the total draw of the amp(s), and use a fuse based on the total current as well...as long as the fuse is protecting the wire..and not too small where it will blow during normal use..what harm is it doing?

I am not looking for an aurgument by any means but some of you seem so adamant about this that it is causing me to question if i am properly fusing my installs.

while we are at it can I blow a sub by underpowering it?........KIDDING posted_image

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master5 wrote:

Ok thanks guys..I get the picture. The thing is in the real world where I am in the trenches performing all kinds of installs on a daily basis (not talking about a comp vehicle where there are rules and judging)..I might for example have some "kid off the street" come in to install all his "stuff".

We all live in the real world please stop being so condescending.

Your approach is OK as long as you remember that the fuse is intended to protect the wire and you always use fuse sizes SMALLER than the max capacity of the wire. Anything else is dangerous and unprofessional. Period.

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I apologize if I came off as condescending..I didn't mean it to sound that way. I was using the term "real world" for the particular example where I see amplifiers installed with wire gauge that is larger then required..not that I actually live in the real world and others don't as a comparison...

and I appreciate your response and agree with it 100%.

Thanks

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hahah this one became funny.... but i have a ? for ya DYON

this is the first honestly that i have heard find a fuse according to the wire gauge..."interesting to me"

what ever happend to take the RMS divide by alternator output at idle ?

thanks man just wanted to ask ;) its been along time since i have seen yalls names ;) good to see yall agian

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If we learn from each success and
each failure, then we can improve ourselves

Here's the answer to that, and it's PERFECT:

stevdart wrote:

master5 wrote:

..if the system called for a 4ga wire..and we used a zero gauge..is it understood that we should intentionally put in a larger fuse then required soley based on the wire gauge and not based on the systems maximum draw potential?

The consideration of fuse value is based on the gauge of the wire it protects. If the fuse is NOT chosen with this consideration, other influences were allowed to interfere with the reasoning process.

Why use a fuse or breaker value of 300 to 350 amps on that 1/0 wire if the pull of the gear doesn't support such a large value? You have to answer this yourself with the simple question: Why is there a 1/0 wire installed when all that was needed was 4 gauge? That's an example of faulty reasoning based on the wrong consideration; it's based on the pull of the equipment, not the wire size. Or is it the associated cost of the fuse or breaker that prompts the choice in fuse value? There again, invalid reasoning. And how valid is that 1/0 wire anyway when you've installed a 4 ga. eqivalent fuse in the run? ...or with a breaker that will shut off when the thermal limits of a 4 ga. wire has been reached?

The intent here is to provide the basic principles of why and how. It should be known that the fuse protects the wire, and any mention of the current system's demand on the fuse's ability should not be addressed as it has no bearing on the principle of this wire/fuse safety system. A professionally-installed system should always have the correct safety devices in place for the wires they serve.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

ok ,perfectly understood as well. but back when I worked at a shop that basically did 90% competition vehicles we would often use zero gauge when a 2ga or even 4ga would have sufficed. This never caused any harm, it looked great (well massive wire always does) and the judges appreciated it.

But if the systems demands were lets say for example, 125amp ,I would see no reason to install a 350a fuse..even though according to some here the wire "calls" for it.

In anyone elses opinion, was this improper or unsafe in any way? Keep in mind I am aware that a wire this large was "unnessesary" perhaps..but aside from the other listed benifits of this "overkill"..it added nicely to our profit margin using the larger wire, distribution blocks and terminals.

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master5, like I said before, the fuse is to protect the wire and one should size a fuse with the capabilities of the wire in mind. If the wire is capable of carrying 350 amps, then the purpose of the fuse is to prevent MORE THAN 350 amps from being carried by the wire. This does not mean you NEED a 350 amp fuse, just that you must not allow more than that. Will your 125 amp fuse do this job? Sure. It's called being logical and understanding electrical safety requirements.

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Thanks for the response, understood posted_image

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I'll chime in with a question related to a DIY build up 'cause i am at this stage, and you all seem to know the right answer. I am installing a PDX 1.1000 amp right now and the wiring will probably be 4 ga at the amp. however, I intend to add another PDX 2.150 or 4.150 later (3 months or less) and don't want to re do the wiring later. i would like to understand what my 'best' method to power the sub amp now and future amp(s) later will be for wiring. I am going to assume that the best should be to run 2 ga from the battery now (fused for wire size) to a 2 -4 output distribution block that can run 4 ga out to the amp(s). Then I can run additional wiring from the dist block later as I require it. Grounding will be the same ( I assume). Is there anything technically wrong with this? I am trying to avoid running wire twice and damaging my interior components by removing and replacing them over and over. Also, buying wire twice (cost is always a factor :) ) .

thanks.

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300M Special. Alpine CDA-9856; Infinity Ref 1252W (2)...so far

That's actually a great idea, and I'm basically doing the same with mine. I will have 4ga going back to the trunk, to a fused distribution block. From there, I can add 8ga wires and appropriate fuses to run to any additional amps or whatever I install down the road. For now it will go from 4ga to a single 8ga for my sub amp, but I'm adding a small 4ch amp for the highs and I can simply tap into that distribution block for power, rather than running a wire through the firewall again. I *hate* penetrating firewalls, especially on a volvo chassis where the thing is heavily reinforced. Luckily my car has a rubber boot where the manual models have a clutch pedal, but still... It's under the battery, so it's not fun. It will be nice to run one wire and be done with it. Also, I'm going to run some fans off the distribution block. It should be a very convenient way of doing things.

Yep same here. Basically I "pre-plan" for upgrades by installing a 4ga. or larger and using a distribution block. This way in the future when I add more power..or additonal amps etc. the main wire is already ran saving time and effort.

I will generally use a main fuse based on the power consumption of the device(s) connected to it..although I totally understand the premise of wire size being the determining factor. Once I perform the upgrades I will use the appropriate fuse(s) but I will never use a fuse with a rating that exceeds what the wire gauge can handle...or a wire gauge not up to task..I hope I did not give that impression.

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hey all.

the wiring kit i recently purchased (absolute AB-404, 4 gage amp instalation kit) has a 60A fuse for the main power line.

now..the amplifier i have is 1600watt RMS (5000 watt MAX, although not relevant) which is using the 4 gage wire for power (duh)

should i get a 150A fuse to replace the 60A????

cheers

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=success isnt mesured by the depths of your pockets=

I would say that is a definate yes.

However for an amp with that kind of power a 2ga. minimum may be called for depending on the final ohms load. But regardless I couldn't imagine a 60a fuse lasting the first heavy bass note with that amp.

Good Luck.

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Gday Master

the amp (2 channel>bridged) has two dvc subs (300watt rms each) rigged up to a 4ohm load.

still a 150A fuse?

cheers

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=success isnt mesured by the depths of your pockets=

Well your final load on the amp will be 2ohms when bridged...what is that amp's RMS power rating @ 2ohms? I bet it's pretty darned up there...above 1000w ?

Now using smaller fuses then you need will not hurt anything per say...just become annoying when they keep blowing. Since this thread had established that a 4ga. wire is appropriate to use up to a 150a fuse..that would be the best bet.

If you were using a lower powered amp..lets say 150w RMS....and you happened to be using a 4ga. then I could see no problem using a smaller fuse like a 60a since there would be no reason for it to blow if everything is properly operating and installed. In other words using a larger wire then is required is not going to force more current into the amp..the amp only uses what it needs.

The things to be most concerned about is...A) using a wire that is too small (this can cause voltage drop)...and B) using a fuse that is too large for the WIRE...afterall we would rather a fuse blow then burn up the ride.

Well thats the way I see it anyhow.

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Oh....and cheers to you as well....or how my Sister from Norway does it....."skoal !!!!!"

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posted_image

^^^thats how i've rigged up the subs because the amp is only stable as low as 4ohms when bridged. (1x1600watt RMS)

now i know i should be using 2ga or bigger but 4ga is all that was availiable. i will upgrade to a bigger wire down the track when i install a distribution block to run another amp......or three hehe. i know that the fuse will have to change (later on) as well because of more current the bigger wire will be drawing to power more amps. thats for another time later though.

cheers or 'skoal' lol

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=success isnt mesured by the depths of your pockets=

Series/parallel..perfect...and you are on the right track with considering the upgrade to a 2ga. in the future.

The only area it seems there is some confusion is when you stated "i know that the fuse will have to change (later on) as well because of more current the bigger wire will be drawing to power more amps"

It is NOT the wire that draws current..it is the device you connect to it..in this case a monster of an amplifier, and more in the future. The wire is simply a vessel for this current flow. If the wire is too small (higher gauge) all those "electrons" that are being called upon to do the work increasing the power..well they simply can't fit..they get choked up...rub up against each other and the wire..and you guessed it...heat (yes a wire too small gets hot) and voltage drop.

Although the following analogy oversimplifies the theory...as well as dealing with the speed of electron flow (quite fast..think light speed)..you can look at it this way......

Think of a tunnel..think of the cars as electrons..or the current..the more cars..the more current. What happens if too many cars try to speed into a small tunnnel all at once???? A crash...a mess..traffic stops flowing...or slows down quite a bit.

Now for the opposite...lets say a wire that is bigger then you actually need.....well if a tunnel was so big that there were never enough cars to slow down the traffic..that would not hurt anything...right? But it is overkill...you would be taking up real estate for a tunnel bigger then required (unless of course you are planning for the future when there is going to be more traffic).

If the wire is bigger then you need..it hurts nothing..has no effect on current flow at all...the current that is needed by the device (amp) will effortlessly flow...unless the fuse (toll booth..lol) is too small for the car...what happens??

Ok I think you get it now...cheers, skoal and salute...aye,lol

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i now know the physics on current flow etc. good description for a newb like myself...

but on another topic.

-amplifiers. 'RCA output'-

my amplifier has RCA outputs near the input. now. can i hook up another amplifier using those rca output on the amp?

or will i have to get a high level converter for the new amp

obviously ill be getting bigger wire or running a different power cable to run this amp.

it is a 150watt rms x4 stable to 4ohms. not sure of brand but thats the type of amp im looking for.

yes....slightly less power draining than the 1600watt rms model running the subs i have currently got. this other amp is for the 6x9 speakers and components in the car.

wiould the rca outputs on the other amp be able to use to send the signal to the other amplifier?

cheers mate

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=success isnt mesured by the depths of your pockets=

Hi All,

Installing a new system in my car, gotta love spending money, and have just got a couple of wiring kits. my plan was to run a 4 guage wire from the batt to a distribution block and then run two 8 guage wires to my amps. Now with my 4 guage wire i got an 80amp fuse and with the two 8 guage i got two 60 amp fuses. Now from what you've said running the fuses would be fine as they will be lower then the capacity of the wires and i would be able to run the two 60amps after the distribution block (thanks DYohn, would have missed that otherwise.) however according to the RMS to Current Draw i will be running more than 80 amps through the main wire and more than 60 amps through one of the 8 guage (2 amps are 4x100RMS and 2x125RMS).

So my questions; will i be blowing up fuses when there is nothing wrong if i install what i've got? should i go and buy a 120-150amp fuse for the main cable and put the 80amp fuse on the 4 channel amp? and are the fuses being packed in these kits significantly less then the wires capacity on purpose to stop people without access to the 12volt killing themselves?

Apologies for the newbie question, i think my bigger fuse method is right but would love to get your advice. have been reading the site for about 2 months now, been fantastc. Bit off topic but doing up a Feroza for some reason and now on the sound part, hoping to take some photos and show off my progress, trying my hand at box building, fiberglassing and lights/presentation thanks to the site.

Cheers,

Danger

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Danger Williams
Diahatsu Feroza 1990
Blaupunkt Amp, Splits and 6x9s
Pioneer Amp and Subs

Fuse Size?