Thread: Should distribution block fuses be used?!?

any time there is a change in wire gauge, I fuse.

It's the smart thing to do.

Buying a fuse block and a fuse is extremely cheap insurance.

I'm fairly surprised Crutchfield would post something like that...then again....Car Audio and Electronics has published some pretty stupid stuff too....

Originally Posted by lexdiamond20

Was just on Crutchfield.com and read this:

Q: Do I need a separate fuse block too?

A: A safe system will have the right fuses installed at each amplifier and also on the power cable by the battery. But if you've ever taken a peek at some competition-style car audio systems, you may have noticed fuses at a third location — in a fuse block by the components. Sure this hardware looks good, but is it necessary?

Unless your amplifiers are among the few that don't come with fuses installed, the answer is no. The reason you see these "redundant" fuses is that in the early days of car audio competition, amplifiers frequently didn't include their own fuses, or if they did, often hid them behind panels that were hard to get to, especially in the heat of competition.

Today, the use of such fuse blocks is largely a matter of style. But that's OK — looking cool definitely counts. In the world of car audio, it's a close third, right behind being safe and sounding great.

I wholly disagree with Crutchfield. The fuses are there for a lot more than just "good looks".

The purpose of fuses on power lines is to protect the wiring, not the components. The fuse will blow, preventing higher-than-rated current from flowing through that power line, which could heat up the wire to the point of causing a fire, melting insulation and causing a short, and possibly worse.

I currently have a fused distribution block getting 4ga wire from my battery (fused at the battery) and sending out two 8ga wires to power my amp and invertor. Though both components have onboard fuses, it was my understanding that the power wire coming form the distr. block to the components needed to be fused in order to prevent fire in the car. Should I stick with getting fuses for the distr. block or will they be a waste of time as the pasted text indicates?

The fuses onboard your components are there to protect the component only. If there is a short (I hope not!) that sends too much voltage down one of the lines, the component fuse will blow first, protecting the equipment. There could still be current flowing down the power line, and if that current is more than the wire can handle, you still have the fire risk.

Yeah, the mistake in the above by Car Audio is that it assumes the fault at or after the amp (indeed where most such faults occur in well-run wiring)...but a partial fault to ground along some 8-guage wire run to an amp of, say, even .1 ohms will cause quite a bit of localized heating near the fault, certainly enough to melt the nearby insulation away, and may not be enough to cause, say, a 200-amp fuse at the battery part. But then again, there's nothing that protects the larger gauge wire before that from doing the same thing except the battery fuse and the fact that the wire is rated for more current and thus more well-insulated against such heating.

For these types of faults, there's really not much you can do to prevent ALL danger...but prudent wire running using proper gauges as well as fused components will get you 90% of the way there. Fusing separate wire sizes adds a small amount of protection, but add protection it does.

I have a later issue of CA&E that says fusing is there to protect wire sizes as they get smaller.

Originally Posted by rationalpi

The cable that run from the distribution block is short, should only be at most 3 - 4 feet. which can support way more amp then the 20+ feet 4 gauge wire. So the fuse or breaker you have set up on you main power wire should be more the enough to keep the wire from causing a fire.

What does length have to do with it?

The longer the wire, the greater the overall resistance of that wire, and the less current it can handle.

As for fused distro blocks, sure, they are not REQUIRED, but a fuse at the battery is not REQUIRED for a system to run, but it sure as heck offers a great deal of safety. A fuse at the distro block offers safety as well.

So, the question really is whether your car and audio setup is worth the extra $50 or so price premium that a fused distro block is over a regular distro block. My choice is that my car is definitely worth the extra $50 for the added safety.

Dave

Originally Posted by Caelric

The longer the wire, the greater the overall resistance of that wire, and the less current it can handle.

As length of wire increases, so does volume, and surface area over which heat is dissipated. At the same current, whether the wire is ten feet or ten inches, it will dissipate the same heat per unit volume or surface area, and thus fail at or very near the same current level.

As a matter of fact, the longer the distance to fault, the more resistance in the wire, and thus, the less fault current the wire will experience. A longer wire is somewhat safer in this regard.