“What gauge wire is right for my amp?”
“How much wire do I need?”
“What size fuse do I need to use for the inline fuse holder?”
Well, don’t Worry! Below we’ll make things as clear as possible for you so there’s no room for confusion.
First, we can’t stress enough how important it is to use the correct wire connections when you’re building an aftermarket car audio system. You also don’t want to go cheap on your amp wiring kit. Don’t you want to get all the power you paid for?
The right wires ensure that the strongest signal is going to the correct destination, and that a sufficient amount of power is being sent to the receiving audio components.
To put simply, the more power an amplifier needs to operate correctly, the larger its power and ground wiring must be. That’s because a 0 gauge wire can accommodate higher demand for electrical current than an 8 gauge power wire.
What gauge power wire to use for power cabling depends mainly on how much wattage your car audio system requires, and on how long the wiring run will be.
As a general rule of thumb, we follow the guidelines below as a quick reference in determining what gauge wire to use.
|Wire Gauge Size||Total Amplifier RMS Wattage (Watts)|
What gauge wire for amp – detailed formula
In order to determine the appropriate wire gauge, first you have to figure out the current draw (in amperes) of your amplifier (or amplifiers). To do that:
- Find the total RMS power of each amplifier:
- Monoblock Amplifier: In case you have on single mono-channel amplifier, then its RMS power of the single channel will be the wattage you will reference.
- Multi-channel Amplifier: Take the RMS output (in watts) of one channel, and multiply it by the total number of channels that amplifier has. For example, if you have a five channel amp with 50 watts RMS per channel, then 5-Channels x 50 watts = 250 watts RMS.
- Calculate the total RMS power of your entire audio system. If you have multiple amplifiers, add up the total power figures to reach a grand total. If you only have one single amplifier, then the total value you found in the first step is all you need.
- Double your grand total power (multiply by 2).
- Divide the outcome by 13.8 (why 13.8? we’ll get to that down below).
The final figure is your car audio system’s approximate current draw. Now, compare this number to the numbers in the “Amperes” column in the chart below. Also, take into consideration the distance from your car battery to the amplifier mounting location.
The distance is usually longer in larger vehicles – around 20 feet – if you plan on mounting your amp in the trunk. So, after determining the distance from your car battery to the amplifier, you will find the appropriate gauge wire for your car audio system.
Please note that the smaller the gauge number, the larger the wire.
A more detailed explanation
I know that you might have several questions – “Why do we double the grand total power?”, – “Why do we divide the outcome by 13.8?”, – “Why wire size and length matter?”
Here are the answers, in case you want more details.
Why double your grand total power?
Simply put: because no amplifier is 100% efficient. Typical analog amps are about 50% efficient. What this means is that about 50% of the power it generates is lost as heat while only half of that power is turned into audio output.
In other words, if your amp is putting out 300 watts RMS, it’s actually drawing about 600 watts or so of power from its source, that’s the reason why the amp’s wiring must be big enough to handle that current draw.
Here, we assume that your vehicle’s electrical system voltage is at 13.8 instead of 12-volt, because again we’re assuming that your vehicle is running, thereby, its alternator will increase the system voltage to around 13.8 volts.
Why wire size matters?
The reason different cable lengths have different ratings due to the electrical resistance – Resistance is an electrical quantity that measures how the material reduces the electric current flow through it – electrical resistance is inherent in cables.
The longer or the thinner a wire, the higher its electrical resistance. A 5 foot cable should have less electrical resistance than say 20ft cable.
Why wire length matters?
If you’re amp requires a 2-gauge wire and you only use an 8-gauge wire, you’ll get poor performance. This will may result in a significantly shorter service life of the other components (your amp and speakers).
Using a big wire gauge where only a small one is required won’t do any harm, however, that kind of overkill would be a waste of money.
What wire gauge to use for speakers?
Speakers wiring also matters. You don’t want the signal and power coming out of your amplifier to be impeded on their way to your speakers and subs. For speakers, we usually use 18-, 16-, or 14-gauge wires. For subwoofers, we use 16-, 14-, or 12-gauge wires.
Why should you invest in a quality amplifier power wire?
Car amp wiring kits are one product that really does abide by the rule “you get what you pay for”. We’ve took a closer look on both cheap and expensive car amp wiring and we’ve found that cheap amplifier wiring has some aluminum mixed in the strands, and it’s pretty well-known that aluminum isn’t as conductive as copper.
That’s why cheap power wires aren’t capable of carrying as much current as quality, oxygen free copper wires. Additionally, cheap amp wires have way much less shielding and are feather light compared to quality amp copper wire.
Holding both cheap and quality amp kits in hands, the latter should feel significantly heavier. Simply because oxygen free copper is pretty heavier than aluminum. That’s one way to tell which is better.
Bear in mind that if your amp is starving for more power than what cables can sustain, you’ll risk clipping the amp, which can lead to distortion and might even blow your speakers. Refer to the chart we included above to determine the right gauge wire for your amp.
Besides using an appropriate gauge wire and ground wire for your car amplifier, you also need to get the right size fuse for your inline fuse holder.
How to choose the right amp inline fuse holder?
Fuse holders play a major role in keeping your components safe. When the power load exceeds the level that these electronic component can support, any electronic device without an inline fuse of some sort will most likely burn up. If use an inline holder, however, the filament inside the fuse will melt down or burn out cutting the current flow to the electronic device it’s meant to protect – amp(s) in our case.
So, what’s the right size fuse for your inline fuse holder? It’s quite easy to figure out which size fuse is right for you. If you have two 40 amp fuses on your amp side, you’d want to have an 80 amp inline fuse on your power wire.
There are various types of inline fuse holders
|Fuse Holder Type||Description|
|AGU||They're usually available in 40 amp, 60 amp or 80 amp ratings and are designed for fuse holders that can accommodate 4 gauge and 8 gauge wire.|
|MIDI||MIDI style fuse feature two hooks - one at each side - they're usually found in 40 amp, 60 amp, 80 amp, 100 amp, 120 amp, and 150 amp ratings.
They are designed for fuse holders that can accommodate 4 gauge and 8 gauge wire.
|ANL||These are meant for high output car audio systems. They look like MIDI fuses with two hooks, one at each end. They're available in 100 amp, 125 amp, 150 amp, 200 amp, 250 amp and 300 amp ratings.
Fuse holders designed for ANL style fuses can accommodate either 0 gauge, 2 gauge or 4 gauge.