Do I Need a Car Amp Fuse?

car amp fuse
The safest way to wire in a power amp is with an inline car amp fuse at the battery. Image courtesy of Andy Arthur, via Flickr (Creative Commons 2.0)

Most cars come with very basic audio systems that only include a head unit and four speakers, so upgrading beyond that is more complicated than simply replacing old components with new ones. If your car didn't come from the factory with an amplifier, and it probably didn't, that means you need to wire it in to power and ground, and that means you need some type of amplifier fuse.

Who Needs an Car Audio Amplifier Fuse?

If your new power amp came with a built-in fuse, that’s great. However, that fuse is meant to protect the amp itself, and it won’t do anything to protect the rest of the wiring in your car. Of particular concern is the amplifier’s own power wire, which could potentially short out somewhere down the line.

If you aren't careful when running a power wire for your new amp, and it shorts out, and it isn't fused, you could be looking at significant damage. In a worst case scenario, a shorted out amp power wire could even cause a fire.

Even if you are careful, simply driving around on the smoothest of roads causes everything in your car to bump and jostle around a whole lot. Wires shift over time, and abrade against each other and other things, which can cause even the best laid of plans to go awry. That's why the fuse is one of the most vital parts of amp wiring.

Connecting Your Amp to Power

It might be tempting to just hook up your new amp to the existing fuse box in your car, especially if the fuse block is located under the dash. It’s certainly easier than running a whole new power cable all the way to the battery, but you need to resist the urge to take this shortcut.

The reason that you should avoid connecting an amp to the fuse box inside your car, and especially never connect to an existing circuit or fuse, is that your amp is almost certainly going to draw more amperage than the wiring in your fuse box is designed to carry.

That means you’re risking a potentially catastrophic failure, even if you swap out a smaller fuse for a bigger one, or use an empty slot in your fuse box.

The issue at hand is closely tied into the way fuses work and the problem they’re designed to take care of. In most basic terms, a fuse is a component that’s designed to fail in order to protect everything else in the circuit. If any component in the circuit draws too much amperage, or a short circuit results in a sudden amperage spike, the fuse will “blow” and interrupt the circuit.

If there is no fuse present, or the fuse fails to break the circuit due to arcing, then other components may be damaged, or there may even be an electrical fire.

The Right Car Amp Fuse Location

Since car audio amplifiers draw a lot of amperage, wiring one in improperly can result in overloaded power wires, shorts, and even electrical fires. That’s why it’s a good idea to run a separate power wire all the way from your battery to your amp.

If you have multiple amps, you can run a single power wire and use a distribution block, but the power cable has to be thick enough to handle the current draw from all of the amps that it feeds.

If there is ever an issue with one of your amps, or your amp power cable shorts out, the results could be potentially catastrophic. In a worst case scenario, the car could catch on fire, or the battery could even explode.

That’s why it’s necessary to install an in-line fuse between the battery and the power cable, and it’s also why you should place that fuse at the battery instead of at the amp. If you place the fuse at the amp, and the cable shorts out somewhere between the battery and the fuse, then the fuse won’t provide any protection at all.

The Right Car Amp Fuse Size

In addition to placing your fuse in the right place, it’s also important to use the right size fuse. If you use a fuse that’s too small, it will blow during normal operation. On the other hand, if you use a fuse that’s too big, you could end up dealing with component failure or an electrical fire.

If your amplifier has an internal fuse, then your inline car amp fuse should be a little bit larger. For instance, you might want to use a 25 or 30 amp inline fuse if your amp has an internal 20 amp fuse.

If you have two amps that both have internal 20 amp fuses, then you should add those numbers together to figure out the right size for your inline fuse. That gives you a little bit of wiggle room without opening yourself up to a dangerous situation.

Some amplifiers don’t have internal fuses, in which case you’ll need to check the power ratings of your amp to determine the right size for your inline car amp fuse.

If you’re dealing with an amp that doesn't have an internal fuse, or even multiple amps that don’t have built-in fuses, you should also consider using a fused distribution block. In the same way that the inline fuse protects you from a shorted out power wire, a fused distribution block will protect your other amps and related components if one of your amps fails.

Types of Fuses For Amps

Most amplifiers that have internal fuses use some type of automotive fuse. These are the same type of fuses that are used elsewhere in your car, and other audio components, like your head unit, may also use very similar fuses.

When you install an inline fuse, you can use this same type of blade fuse. The fuse itself is installed in a fuse holder, which you connect in-line with the amp power line.

The other option is to use an in-line barrel fuse. This also uses a fuse holder that you install in-line with the power wire, but it will typically take the form of a clear or translucent plastic tube that holds a barrel fuse.

Regardless of the type of fuse you use, it's important to select a fuse holder that meets or exceeds the rating of the fuse that you plan on installing. If you determine that you need a 30 amp inline fuse, don't install a fuse holder that's only rated for 25 amps.