*As an Amazon Associate, this site earns from qualifying purchases. Learn More.

What Size Fuse to Use for Your Amplifier Power Wire

Almost all cars these days come with factory-installed stereo systems, and while these work relatively well, they are usually basic units that are nothing to write home about, sound quality wise.

Most often, factory-installed audio systems include only a head unit and a couple of speakers, so upgrading beyond that is more complicated than simply swapping out old components with new aftermarket ones.

If your car didn’t come from the factory with an amplifier, and there’s a good chance it didn’t, you need to wire it into power and ground. That means you need some type of amplifier fuse.

What size fuse to use depends to a great extent on several things including the material, thickness (gauge), and length of the power and ground wires used for your amplifier’s installation.

Here’s everything you need to know about which fuse you should use for your amp’s wiring, and why.

What Is a Fuse Used For?

A fuse is an expendable electrical safety device that is designed to become a permanent open circuit when exposed to excessive current.

Generally speaking, fuses are used to protect much more expensive electrical components from electrical overloads, which could damage components or wiring and potentially cause a fire.

When it comes to vehicles, a fuse is meant to protect you and your car from a catastrophic electrical disaster. I mean, think about it, a car amp’s 12 volt power wiring can carry enough electrical current to cause significant damage not only to the wires themselves, but also to your car. In a worst-case scenario, a shorted-out power wire could cause a fire.

Additionally, driving with a tank filled with gasoline is already dangerous enough, as that could easily catch fire or explode in the event of an accident. You certainly don’t want to make things worse by adding the threat of an electrical fire occurring under the same circumstances. This is the reason why using a fuse is one of the most vital parts of amp wiring.

Since car amplifiers draw massive amounts of current, wiring one improperly can result in overloaded power wires, shorts, or even electrical fires. Thus, in order to protect you and your car from an electrical disaster, an in-line fuse must be installed between the battery and the power cable — as close to the car’s battery as possible.

What Does a Car Amp Fuse Do?

It goes without saying that the answers to most questions regarding amp fuses include the word “safety.” While most car amplifiers do come with built-in fuses, these fuses have one main purpose and that is to protect only the amps themselves.

That is to say you need to consider installing an additional in-line fuse between the amp and the the battery to protect the power wiring, your car, and yourself against fire, in the event of an electrical mishap.

So, to answer the question, What does a car amp fuse do?, the answer is it blows out and interrupts the circuit by stopping the flow of current.

Fuses are dirt cheap and are a lot easier to replace than your car or your life. So, given the alternatives, “blowing a fuse” is a blessing in disguise.

Once a car amplifier fuse is blown, it must be replaced with a fuse of the same specification to ensure the circuit is properly protected.

Keep in mind that when an in-line fuse blows, you should thank it for saving your life, and then it’s critical to figure out why it had to sacrifice itself, before you even consider replacing it.

When a fuse blows, something must be wrong. It just doesn’t make sense to replace a fuse that’ll just blow again because the underlying problem (e.g loose or frayed wire) was never fixed.

Why Should You Use an In-line Fuse?

Like other types of fuses, the main purpose of an in-line fuse is to protect the wiring from overheating when excessive current flows through the amp wire.

Additionally, an in-line fuse is also meant to protect your vehicle and its electrical equipment from the dangers of a short circuit. A short circuit occurs when a positive current-bearing wire comes in contact with bare metal (like your car chassis).

Because your entire car chassis can be considered “negative” or ground, you can think of a short circuit as positive touching negative.

This is the last thing you want to happen, but even if it does happen, a properly installed fuse will prevent a fire or other damage.

Types of Fuses for Amps

There are three main types of fuses used in car audio. Each of which is best suited to different applications and electrical equipment within a vehicle.

AGU fuse

This is the most common type of fuse. An AGU fuse is a cylinder shaped fuse with either metal caps at both ends. The metal caps are the contact points. They’re are connected by a fuse element that’s meant to melt in the event of an over-current event. The fuse link is encased in a translucent glass/plastic tube which makes it really easy to visually determine if the fuse is blown.

Automotive fuse (Blade fuse)

Sometimes called spade or plug-in fuses, automotive blade fuses specifically designed for automotive systems. They come in ‘blade’ form (a transparent plastic body with two flat prongs that fit into sockets) and are color coded according to rated current.

Most car amplifiers with built-in fuse use automotive fuses. Other audio components, like the head unit, might use similar fuses.

Automotive fuses are generally rated for circuits no higher than 32V DC, but some types are rated for 42-volt electrical systems.

ANL fuse

ANL fuses are the most common types of fuses used in car audio systems. These fuses are usually used in large fuse holders and are run in-line between the battery and the amplifier.

ANL fuses have the highest capacity of any fuse type, which makes them ideal for high wattage systems.

 

P.S: Keep in mind that regardless of the type of fuse you use, it’s important to opt for a fuse holder that meets or slightly exceeds the rating of the fuse you plan to install. If your system ,for example, requires a 40-amp inline fuse, don’t install a fuse holder that’s rated for only 35 amps.

 

Fuse Size Matters

A common car audio question we often get is, “What fuse size should I use for my amp power wire?“.

This is not an easy question to answer. Several things must be factored in in order to determine the right fuse size for your power wire including your amp’s current draw, the material, thickness (gauge), and length of the power and ground wires used for your amplifier’s installation.

The fuse must be able to handle the power that flows through the amplifier’s power wire under maximum operating conditions (full power) and no more (ideally).

Choosing a fuse size that is too large will not provide adequate protection and choosing one that is too small will blow more often than it should. Here’s a few guidelines you need to take into account when sizing the main power fuse for your amplifier.

First of all, to determine the right fuse size, you will need to know the current draw (amperage) of each part of the system that draws power from the main power wire. For example, if you have two amplifiers drawing 60 amps each, you’d want to use a 120 amp fuse. You should be able to find the maximum current draw of your amplifier(s) in the amplifier’s owners manual.

But what if the maximum current draw of your amp(s) is greater than one value of fuse but less than another (i.e. 160 amp)?

Well, in that case, you have the option of either choosing a 150 amp fuse or a 175 amp fuse. To reduce the chance of accidental fuse blows, you can choose the larger fuse. However you may also opt for a smaller fuse for greater short circuit protection. Just keep in mind that if your amplifier fuse keeps blowing out every now and then, you’ll probably need to move up to the next size. But if you’re using the right sized fuse for your current draw and it keeps blowing out, you may have another problem that needs to be addressed.

But what if your amplifier has an internal fuse?

Well, if your amplifier comes with a built-in fuse, your inline car amp fuse should be slightly larger. For example, if your amp’s internal fuse is 20-amp, use a 25- or 30-amp inline fuse.

If you have multiple amps with internal fuses, add the amperage ratings together to figure out the right size for your inline fuse.

For safety reasons, your amplifier power wire should use a fuse sized equal (ideally) to the maximum amperage ratings listed in the chart below.

Power wire Max fuse size
00 AWG 400A
0 AWG 325A
2 AWG 200A
4 AWG 125A
8 AWG 50A
10 AWG35A
12 AWG 20A
14 AWG 15A
16 AWG 7.5A
18 AWG 5A

The chart above should be used only as a general guideline. This is because most manufacturers rate their wires differently.

So, when discrepancies occur concerning what fuse size to use, always go for the wire manufacturers’ fuse recommendations. If you’re using an amplifier wiring kit, use the fuse that came with the kit.

For safe installations, if you find one or more blown fuses, it’s important to replace it with a fuse of the same size and rating. Using a smaller fuse than what is recommended can cause it to blow out faster during normal operation. If you use a fuse that’s too large, you could end up with component failure. Replacement with a fuse that’s too large also poses a real fire risk.

How to Select the Proper Fuse Size for Amp Wire

For those of you who want to get right down to business, let’s not waste any more time, here’s how you’d go about determining fuse size for amp wire correctly.

1. Determine Your Wire’s Current Carrying Capacity

The very first thing you need to do is to figure out your wire size’s maximum amperage capacity. Refer to this article to look up the rated amperage of different sizes and types of wires.

Keep in mind that the current carrying capacity of a wire is defined as the amperage a conductor can carry before melting either the conductor or the insulation. Every kind of wire has a limit to how much current it can safely handle before over-heating.

Since most people use 1/0 gauge wire, we will use that as an example. The maximum amperage for 1/0 gauge wires is 350 amps.

2. Understand the Point of the Fuse

As mentioned above, the main purpose of a fuse is to blow or melt before the overcurrent causes a fire or damages something valuable.

With that in mind, always make sure the fuse you’re using is not larger than the maximum capacity of the wire, as you want the fuse to blow before the wire burns. So right now we are looking at fuses under 350amps.

P.S: When you’re dealing with a fuse size greater than 300amps or so, you’ll probably be looking at ANL fuses, not automotive fuses (Blade fuses) or AGU (the cylinder ones).

 

3. Determine the Maximum Current Draw (Amperage) of Your Amp(s)

To figure out the maximum current draw (amps), we have some calculations to do. So, let’s say you have a 1,200watt Class D mono amp powering your subwoofer, and a 400watt Class A/B amplifier driving your speakers.

To calculate the estimated current draw (amps) that each of these amplifier will require, here is a quick calculation.

A.) Take each amplifier, one at a time, and divide the RMS rating of each of them by 12 volt. (More realistically, your car runs at about 13.8volts, but to be safe, divide by 12. You could calculate for both 12volts and 13.8volts and average the two, but for the sake of simplicity we are just looking for a ballpark figure).

P.S : Keep in mind that a fuse or a breaker can actually handle much more than its rated amperage in short bursts. So, using amplifier peak wattage isn’t going yo give you ideal protection. Instead of that, we use RMS rating to determine the right fuse size to use for your amplifier.

 

Fuse size = Rated power / Voltage

  • Class D Amplifier: 1,200(watts RMS)/12(volts) = 100 amperes (or amps)
  • Class AB Amplifier: 400(watts RMS)/12(volts) = 33 amperes (or amps)

B.) Next, you want to factor in amplifier’s efficiency. Class D amplifiers are extremely efficient. They can reach peak efficiencies of 90% or greater. So take your figure from your class D amp, 125amps, and multiply it by .1 (or 10%) to take efficiency into account.

  • 100amps * .1 (class D amp efficiency) = 10amps

Let’s add this result to to the original one.

100amps(from the RMS Of class D amplifier divided by 12V) + 10amps (the class D efficiency) which gives you 110amps.

So, you class D amplifier will draw around 110amps.


Now, let’s do the math for the class A/B amplifier.

Class A/B amplifiers are about 60% efficient, so multiply the original figure by .4 (40%)

  • 33amps * .4 (class A/B amp efficiency) = 13amps

Next, add 33amps (from the RMS Of class AB amplifier divided by 12V) to the 13amp (Class A/B efficiency) = 46amps.

So, your class AB amplifier will draw around 46amps.

C.) The final result is 110amps for you class D amp, and 46amps for your class A/B amp. Therefore, your car audio system will draw around 156amps, at full RMS and at 12Volts (although when your engine is running, you are more at around 13.8volts, which would give us a smaller figure than 156, more around 135 amperes or so).

4.) In-line Fuses Should be Larger Than Your System Amperage 

Generally speaking, your in-line fuse must be rated slightly above what your audio system will draw. This is especially true if your amp(s) have an internal fuse.

In our case here, the system will draw approximately 156amps. Therefore our fuse must be under 350amps, and over 156amps.

A 200amp or 250amp fuse would be fine for this situation, most people go with a 250amp fuse on 1/0gauge.

What’s the Proper Car Amp Fuse Location?

The main function of the in-line fuse is to protect the main power wire. Without this fuse, a short in the main power wire could cause excessive current and heat build-up to ignite the wire and eventually the vehicle.

The recommended practice is to place the in-line fuse near the battery, preferably within eighteen inches from the battery but the shorter the better.

The reason why it’s of paramount importance to have your amplifier’s in-line fuse as close to the positive terminal of the battery as possible is because you want the whole circuit to be dead if the fuse blows.

Since the vehicle’s chassis and metal body parts are all bonded to the negative terminal of the battery, and therefore they are considered “ground” or “negative”, when a power wire frays or comes loose for example in the event of an accident and touches metal, it’ll easily create a short circuit, which in turn could set the vehicle on fire. This is why you want the distance between the battery clamp and the main power fuse to be as short as possible.

Frequently Asked Questions

What Size Fuse to Use for 3000 Watt Amp?

Let’s assume that you car’s voltage (with the engine turned on) is around 13.5V, and that you have a Class D amplifier pumping out 200W RMS power, What size fuse is adequate for this amp? Let’s find out:

Let’s use the formula mentioned above and do some calculations:

  • Rated power / Voltage = Fuse size

3000 watts / 13.5V = 222 amperes (or amps)

Now, let’s take class D amp efficiency (90%) into account:

222amps * .1 (class D amp efficiency) = 22 amperes

Let’s add this result to to the original one.

222amps(from the RMS Of class D amplifier divided by 13.5V) + 22amps (the class D efficiency) which gives you 244amps.

So, you class D amplifier will draw approximately around 244amps.

What Size Fuse to Use for 2000 Watt Amp?

Assuming that your car’s voltage (when the engine is running) is around 13.5V, and that you have a class D amplifier rated at 2000 watts RMS, What size fuse should you use for this?

Well, let’s use the formula mentioned above and do the math.

  • Rated power / Voltage = Fuse size

2000 watts / 13.5V = 148 amperes (or amps)

Let’s not forget to factor in class D amplifier’s efficiency of 90%.

148amps * .1 (class D amp efficiency) = 14.8 amperes

Let’s add this result to the original one.

148amps(from the RMS Of class D amplifier divided by 13.5V) + 14.8amps (class D efficiency) which gives you 162.8amps.

So, you class D amplifier will draw around 162.8 amperes.

What Size Fuse to Use for 1000 Watt Amp?

Let’s say your car voltage (when the engine is running) is around 13.5V, and that you have a class D amplifier rated at 1000 watts RMS, What size fuse should you use for this?

Well, let’s use the formula mentioned above and do the math.

  • Rated power / Voltage = Fuse size

1000 watts / 13.5V = 74 amperes (or amps)

Next, let’s factor in class D amplifier’s efficiency of 90%.

74amps * .1 (class D amp efficiency) = 7.4amps

Let’s add this result to to the original one.

74amps(from the RMS Of class D amplifier divided by 13.5V) + 7.4amps (class D efficiency) which gives you 81.4amps.

So, you class D amplifier will draw approximately 81.4 amperes.

What Size Fuse to Use for 500 Watt Amp?

Let’s assume your car voltage (when the engine is running) is around 13.5V, and that you have a class D amplifier rated at 500 watts RMS, What size fuse should you use for this amp?

Well, let’s use the formula mentioned above and do the math.

  • Rated power / Voltage = Fuse size

500 watts / 13.5 = 37 amperes

Let’s factor in class D amplifier’s efficiency of 90%.

37 amperes * .1 (class d amp efficiency) = 3.7 amperes.

Let’s add this result to to the original one.

37amps(from the RMS Of class D amplifier divided by 13.5V) + 3.7amps (class D efficiency) which gives you 40.7amps.

So, at 500 watts RMS, this class D amplifier will draw approximately 40.7 amperes.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

Leave a Reply

Your email address will not be published.

Back to top button