Most people get caught up on fuse wire size but once you get the hang of it, it shouldn’t cause too many headaches. This is an in-depth fuse tutorial explaining everything you need to know about fuses and how to size a fuse. We’ll go into all the relevant details and what it all means so you’ll go from novice to pro in no time at all.

Why do you need a fuse?

The main function of a fuse is to protect your wiring, but in order to do so, you’ll have to get the right fuse wire size from the start, too low and it’ll blow, too high and you’ll end up doing damage to the whole circuit!

Things could get really ugly really quickly, so to avoid all that mess you’ll need to ensure that you get the right size fuse for the job every time. For your fuse to do its job correctly and protect your wires, it should be rated about 1.1 to 1.5 times the rated current value. It’s also a great idea to get an ATC fuse holder to protect and mount your fuse.

One common misconception about choosing the correct fuse size is that it’s dependent on the load of the circuit. Actually, the load of the circuit should have nothing to do with choosing a fuse size. The fuse size should be based on the SMALLEST wire (largest gage number) in the circuit.

How to calculate fuse rating

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 calculating fuse size correctly in 3 simple steps:

  • Determine the wire gage you already have by locating it on the package or simply by measuring it.
  • Use the following table to determine the maximum current for whatever wire gage is being used.
  • Take the maximum current value obtained from the table and find the largest fuse you can find that still falls within the limitations. DO NOT EXCEED THE VALUES ON THIS TABLE! Common automotive blade-style fuses exist at 5A-20A in 5A Increments. Ex: 5A,10A,15A,20A

Determining the Total Amperage of your Circuit 

So you just bought your stuff at Oznium and are getting ready to plan your installation while USPS gets it to your door. One of the first questions to ask when planning your installation is what size wire to use, which will later determine what fuse to use. 

Don’t worry if you’re lost, you’re at Oznium, we’re helpful here

Current is measured in Amperes, abbreviated to Amps or just the letter A. Because of the low-current nature of the products at Oznium, most of the products, and the table that I’ve developed, have current listed in milliamperes or mA for short. 

eg. 1A is equal to 1000mA 

To find the total amperage in your specific installation, refer to the table below.

Find the items that you’re installing and their current requirements. Add the values and divide by 1000 to get your total current in Amps. You can use this value in the fuse size chart above to determine the minimum wire size required.

Here’s an example:

Say you bought a cold cathode kit for each side of the dash (2 Transformers), 5 superflux LED’s for your vents, and a 4.7″ Flexible LED strip for your center console. 

If you want to put all of these on a single circuit, you’ll need to know the current. Based on the table above, each transformer draws 700mA, each Superflux LED draws 80mA, and the LED strip draws 80mA 

Add it all up..

(700*2)+(80*5)+(80*1) = 1880mA in total. 


 1880mA / 1000 = 1.88A. 

Put 1.88A into the top table in this post. That table tells you that you should have no smaller than 21 gauge wire for your circuit. 

Personally, I would go with the 20 gauge wire and a 2.5A fuse.

If I’ve missed anything or left anything out, please correct me through PM, and I will correct the tables. 

What is fuse rating?

You’ll usually find the fuse rating on the side of your fuse, which will be given in amps. Fuse rating is the amount of current needed for the fuse to blow or break. When this happens, it stops the electrical power from flowing through the electrical circuit.

Why are fuses rated?

The fuse rating is a valuable piece of information because it helps you to protect your electrical circuit and therefore should never be neglected. Every electrical circuit will need a different amount of electrical current, what is just right for one electrical circuit may be too much or too little for another. Do the right thing and protect your circuit.

Hopefully this guide helps you to install all the products here at Oznium quickly and most importantly, safely. 

Anyone who needs additional information or has specific or more complex installations, feel free to get in touch or post a question below.

Read common questions and answers on ATC Fuse for LEDs