To protect you and your car from an electrical disaster, a fuse must be installed on the amp power wire — as close to the car's battery as possible.

A fuse will protect you and your car from a catastrophic electrical disaster

It's dangerous enough driving around with a tank loaded with gasoline that could catch fire or explode in the event of an accident, you certainly don't want to add the threat of an electrical fire occurring under the same circumstances.  An in-line fuse on your amplifier's power wire will protect you and your car from almost any electrical disaster related to the amp's installation.

Fuse as close to the battery as possible

In the event of an accident, you wouldn't want a live power wire flopping around inside your car. The vehicle's chassis and metal body parts are all connected to ground, so when a loose power wire touches metal, a short circuit is created that produces runaway current flow and heat build-up. This is why we recommend installing your fuse as close as you can to the positive battery terminal, so no loose ends can cause damage.

Be sure to route the power wire around other things in the engine compartment so it doesn't get in the way. It's also a good idea to secure the power cable and fuse holder to the vehicle body (typically with wire ties) to keep it from bouncing around over time. (In this image, we sat the fuse holder on top of this fuse box simply to get a better photo.)

What's current and why is it dangerous?

To help visualize the concepts, it's often useful to study an electrical circuit as if it were a closed arrangement of pipes filled with flowing water — because similar rules and limitations apply. You can think of electrical current, using the plumbing analogy, as the amount of water inside a given volume of pipe at a particular moment in time. As we pump more and more water inside that section of pipe in that same amount of time, the pressure inside the pipe increases until it reaches the maximum strain capacity of the pipe's construction material, and then the pipe bursts.

Electrical resistance generates heat

Instead of water-flow resistance raising the pressure inside a pipe, electrical resistance to current flow creates heat in the wire. Too much current flowing through a wire's resistance could overwhelm the conductor material or insulation and melt it or set it on fire. Every kind of wire has a limit to how much current it can safely handle before over-heating. 

When a fuse blows, something is wrong

A fuse works by introducing a small weak metallic segment in the power circuit that's designed to pass a rated amount of current, but melt apart, safely breaking the circuit open, when that current rating is exceeded. The fuse is there to protect you.

When a fuse blows, you should thank it for saving your life, and then find out why it had to sacrifice itself, before you replace it. There's no sense in replacing a fuse that'll just blow again because the loose wire that caused the problem in the first place was never fixed.

Note: Sometimes you can't determine whether or not a fuse is blown by visual inspection, and a multimeter or continuity tester must be used to verify a broken connection or that voltage is not present on both sides of the suspect fuse.

Safety note: Never replace a blown fuse with a higher-rated fuse — that could allow the wires and your car to burn to the ground before the fuse blows.

Circuit breakers

Circuit breakers are like fuses that can be re-set without needing replacement. Besides safety reasons, using a circuit breaker can come in handy if you regularly blast competition-level bass at or above your amp's power capacity, or you want a covert system-off switch so valets and mechanics can't play around with your sound system. Some people don't trust  circuit breakers because they take a little longer to trip open than would an equivalent fuse — but that really shouldn't make any difference in a car audio installation.

Maximum and minimum fuse ratings

The smallest fuse that'll work for your system should provide enough current to support your amplifier's maximum power output. The only penalty for using a fuse too small is the expense of replacing fuses that blow when the amp tries to produce its rated power. The largest fuse size to use will protect the power and ground wires from melting while also allowing maximum current flow to the amplifier, letting it produce its maximum output power.

To avoid danger, obey the limits

For safe installations, your power wire should use a fuse sized equal to or less than the maximum amperage ratings listed in the chart below. For information about what size wire to use for your amp installation, refer to our Wire gauge chart.

Power wire	Max fuse size
00 AWG	400A
0 AWG	325A
2 AWG	200A
4 AWG	125A
8 AWG	50A
10 AWG	35A
12 AWG	20A
14 AWG	15A
16 AWG	7.5A
18 AWG	5A

Chart accuracy: The above chart should be used as a general guideline — many manufacturers spec their wires differently. When discrepancies occur, always use the wire manufacturers' fuse recommendations. If you're using an amplifier wiring kit, use the fuse that came with the kit.

Wire material: The chart is for stranded oxygen-free copper (OFC) wire about 15 feet long. Copper-clad aluminum (CCA) and solid copper household-type wiring have different current-carrying capacities, use different-size fuses, and are generally inappropriate for mobile audio applications.

Marine fuses: Regular fuses and circuit breakers often create a small spark when blown or tripped, so would be dangerous in most marine applications and wherever gasoline fumes are present. Marine-grade ignition-protected fuses and breakers are the safest way to protect your wiring when afloat.

What about the fuses onboard the amplifiers?

When fusing your main power wiring, ignore the onboard fuses your amplifiers and other devices may have. Plan your system fusing as if those fuses didn’t exist and use the fuse rated for the main power wire. Those onboard fuses are there to protect the individual devices themselves when something goes wrong internally — so even if an onboard amplifier fuse blows, the power and ground wires near it will still be electrically active and dangerous. Remember, the fuse on the main power wire protects the wiring and your life. When something goes wrong, you want power to shut off for the whole system, including the wiring.

Some amplifiers don't have onboard fuses — for whatever reasons the manufacturers have decided. In multi-amp setups that use power distribution block wiring, each amplifier without an onboard fuse will require, for safety's sake, an additional in-line fuse, rated for the amp's power wire capacity, mounted near the amp itself or the distribution block.

Which one's right for you?

Give us a call when you're purchasing an amplifier and its installation gear, so you can be sure you get the right power wire and fuse for your amplifier to safely play at its maximum potential.