To fuse, or not to fuse, that is the question

[JBurt09]

Alright so I used work at a shop that was huge on fusing.Fuse here, fuse there, fuse everywhere.Not excessively, but fuse where deems appropriate.So that's what I've always done when building.However I have another buddy that owns a very reputable shop that does great quality work that says fusing in certain places is completely unnecessary, such as in this scenario: I have 0 gauge running from the front battery, fused within a foot of the battery, and ran to the back to a distribution block where the 0 gauge comes back out to an amp, and 4 gauge comes out the other side to another amp.Like this build for instance:

Now, according to the shop I work at, they say to fuse before all amps after any distribution block because where one amp may take 250 amps, the other may only take 50 and you want to have a way to make sure all that extra power doesn't find it's way to that smaller amp during a surge of some sort or something.So fuse before the amp after a distribution block.

However, according to my buddy with the other shop, he says fusing after the distribution block is completely unnecessary in all cases UNLESS the amp is not fused, like a lot of Rockford amps, but other than that you don't need to fuse for many reasons such as it is just adding more resistance, the fuse is only for protecting the wire and not the amp, and it makes no sense to "double-fuse".

The Kicker amp is externally fuse with two 20 amp fuses.The Hifonics amp is not.So according to my buddy, there is no reason to fuse the Kicker amp, but should fuse the Hifonics.According to the guys at my shop, fuse both.Some one please clear this particular scenario up for me, and if possible, tell me a few general rules of thumb to remember for these situations on fusing.Thanks ahead of time.

Edited January 19, 2010 by JBurt09

[Boon]

Well.... yes and no... if the wire falls out of the amp the amp fuses aren't doing shit to protect it so the only thing protecting the wire is the (probably much too large) fuse on the main power wire.

Say you have an unfused 8ga coming off a distro that has a 300A fused 0 gauge feeding it. The 8ga will probbbbabbbbblllyyyy still manage to flow the requisite 500 odd amps to blow the 300A fuse but it'll get REALLY hot in the moment it takes to do it.

What will seriously bone you is if it instantly heats up enough that it can only flow, say, 300A. Then it won't blow the fuse up front and instead will just get REALLY REALLY hot. That's the bit where your car burns to the ground.

[JBurt09]

Well.... yes and no... if the wire falls out of the amp the amp fuses aren't doing shit to protect it so the only thing protecting the wire is the (probably much too large) fuse on the main power wire.

Say you have an unfused 8ga coming off a distro that has a 300A fused 0 gauge feeding it. The 8ga will probbbbabbbbblllyyyy still manage to flow the requisite 500 odd amps to blow the 300A fuse but it'll get REALLY hot in the moment it takes to do it.

What will seriously bone you is if it instantly heats up enough that it can only flow, say, 300A. Then it won't blow the fuse up front and instead will just get REALLY REALLY hot. That's the bit where your car burns to the ground.

Thanks for the reply man.I know it was a decent little bit to read through.So, in this instance with the Kicker and Hifonics amp, where the Kicker amp is already fused on the amp with two 20 amp fuses, but the Hifonics amp is not fused, would I only need to technically fuse the Hifonics amp after the distribution block?Technically the 300 amp fuse in the front would still allow almost 500 amps to surge through it, but wouldn't the fuses in the amp blow first, leaving the power to go nowhere else since there is no draw?

I've never seen a car in person that has completely burned to the ground from an audio install gone wrong, but I've seen a few people come in who's "friend" installed their system with fuse blocks that have completely melted down and amps that have gone up in smoke with the internal circuitry totally fried.

[Boon]

Thanks for the reply man.I know it was a decent little bit to read through.So, in this instance with the Kicker and Hifonics amp, where the Kicker amp is already fused on the amp with two 20 amp fuses, but the Hifonics amp is not fused, would I only need to technically fuse the Hifonics amp after the distribution block?Technically the 300 amp fuse in the front would still allow almost 500 amps to surge through it, but wouldn't the fuses in the amp blow first, leaving the power to go nowhere else since there is no draw?

I've never seen a car in person that has completely burned to the ground from an audio install gone wrong, but I've seen a few people come in who's "friend" installed their system with fuse blocks that have completely melted down and amps that have gone up in smoke with the internal circuitry totally fried.

If the power wire falls out of the amp and shorts on the floor the fuses on the amp do NOTHING (obviously )

Most amps will happily completely shit themselves and leave the fuses on the end completely intact

[JBurt09]

If the power wire falls out of the amp and shorts on the floor the fuses on the amp do NOTHING (obviously )

Most amps will happily completely shit themselves and leave the fuses on the end completely intact

Hahahaha that's so reassuring.

Not to sound cocky or arrogant but I think I install well enough for the power wire to not fall out of the amp So was I wrong in what I did in fusing amps in that scenario pictured above by fusing a fused amp?Obviously the fact that the amp is "fused" doesn't really matter, as you stated, but am I just adding resistance and fuses where they don't belong?From what you said, I seem to be right, but do you know why he would feel the way he does about not fusing them?He owns a pretty reputable shop and does nice quality work, I just didn't know why he would think the wrong way about something that should be so basic and well understood.

[Boon]

He probably feels the way you do... that his installs are good enough that the wire from the distro to the amp will NEVER short. Fuse holders are expensive and time consuming.

If you are confident of this fact, don't worry about fusing them.

At the same time, voltage drop across a fuse is pretty damn negligible.

The fuses on the end of the amp are reallllly only there so that they blow if you hook the amp up backwards. I can't see any other reason - most amps will either shit themselves or go into over-current protection before the fuses on the end will blow. I'm yet to EVER pop one, personally.

Occasionally I have seen a Class A/B amp that has dropped a channel and the power supply section has been strong enough that the fuses popped before the FETs in the power supply did but it's fairly rare.

[JBurt09]

He probably feels the way you do... that his installs are good enough that the wire from the distro to the amp will NEVER short. Fuse holders are expensive and time consuming.

If you are confident of this fact, don't worry about fusing them.

At the same time, voltage drop across a fuse is pretty damn negligible.

The fuses on the end of the amp are reallllly only there so that they blow if you hook the amp up backwards. I can't see any other reason - most amps will either shit themselves or go into over-current protection before the fuses on the end will blow. I'm yet to EVER pop one, personally.

Occasionally I have seen a Class A/B amp that has dropped a channel and the power supply section has been strong enough that the fuses popped before the FETs in the power supply did but it's fairly rare.

It's the client that's paying for it, not me, but if it were mine I would much rather pay for a fuse than to have to pay for a new amp.

A lot of people that I have seen like to look at the amperage of the fuses in the side of the amp to get a general idea of what kind of current the amp will pull and put out.Is this in any form a reliable way to get a guesstimate or just an old myth?

And the last thing, for now, is do you agree that fuses/fuse blocks are only used for protecting the wire?I mean sure you don't want to throw a 300 amp ANL fuse on a piece of 10 gauge wire, but I always thought the fuses were mostly for the amps, hence why they make such a wide variety of sizes and ratings.

[jack]

It's the client that's paying for it, not me, but if it were mine I would much rather pay for a fuse than to have to pay for a new amp.

A lot of people that I have seen like to look at the amperage of the fuses in the side of the amp to get a general idea of what kind of current the amp will pull and put out.Is this in any form a reliable way to get a guesstimate or just an old myth?

And the last thing, for now, is do you agree that fuses/fuse blocks are only used for protecting the wire?I mean sure you don't want to throw a 300 amp ANL fuse on a piece of 10 gauge wire, but I always thought the fuses were mostly for the amps, hence why they make such a wide variety of sizes and ratings.

never over-fuse the wire capacity. ther is a sticky in electrical section that gives this info

[JBurt09]

never over-fuse the wire capacity. ther is a sticky in electrical section that gives this info

No I understand that.I was asking if fuses were mainly intended to protect the wire it is connected to or the amp that it delivers power to.For instance, if I have an amp that is only meant to draw 50 amps max and I am running 4 gauge wire that can easily take 150 amps, would you recommend a 50 amp fuse or the 150 amp fuse?That's pretty much my question.

[Boon]

The fuse is only to protect the wire. The amp has, well, protection to protect it

The fuse rating is a reasonable way to guesstimate an amp's power... then again I have seen 1 or 2 amps from shifty chinese companies that had 3 40A fuses... and only 1 was actually connected to the PCB