How-to Size Fuses in a DIY Camper Van Electrical System

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Fuses protect your system from catching on fire in the case of mishaps such as a wire rubbing through it’s insulation and grounding itself to the frame of your camper. The fuse is there to protect the WIRE not the device it’s connected to.  Each device SHOULD have some kind of internal overcurrent protection in addition to the fuse protecting the wire.

Quick note before we get started.  This is just one part of an overarching “How to Install a DIY Camper Van Electrical System” series.  If you’ve just stumbled on this article directly without seeing that, there are likely some things we’ve already covered.  If you want to check out that step by step guide, you can do that here: https://www.explorist.life/diy-campervan-solar

Also, we have interactive solar wiring diagrams that are a complete, A to Z solution for teaching you exactly what parts go where, what size wires to use, fuse size recommendations, wire lug sizes, and all kind of other stuff to help save you time and frustration.  You can check that out here: https://www.explorist.life/solarwiringdiagrams/

TYPES OF FUSES

There are 3 types of 12v fuses I recommend.  They are Spade Fuses, ANL fuses, and Re-settable Breakers.

Spade fuses are the fuses that you’ll commonly find in your car’s fuse panel and are typically for items run out of your distribution block and less than 30 amps (in our case.

Spade Fuses

Spade fuses are what you commonly see in your vehicles fuse block. These are typically used for lower amperage devices and the most common size seems to be 15 amps.

ANL FUSES

ANL fuses come in sizes from 35 – 750 amps.  They are typically less expensive than Re-settable Breakers.  They are more reliable than re-settable breakers as they have no moving parts.  If they blow/trip, they must be replaced.  They require tools to connect/disconnect.

RE-SETTABLE BREAKERS

Re-Settable Breakers come in sizes from 25 amps up to 200 amps.  I prefer these on circuits that I know I may have to regularly ‘disconnect’ for maintenance and or troubleshooting.  Honestly, the only time I don’t use these is when I need a fuse/breaker that is bigger than is available.

HOW TO CHOOSE THE SIZE OF YOUR FUSES

Easiest Way

A lot of components will tell you how big of wire and what kind of fuse to use.  If this is the case, follow it.

Easy Way

  1. Find the continuous amperage of the device you are trying to power and multiply that number by 1.5, then round up to the nearest fuse size you can find.
  2. Cross check that fuse size with the maximum fuse size chart below and verify that your fuse size is below the maximum fuse size listed in the chart.

(more info: ABYC E-911)

Fuse & Wire Sizing Example

For this example, we are going to wire the 12v distribution block to the bus bar then wire a string of lights to the 12v distribution block.  All with appropriately fused with properly sized wires.

Step 1: Find the wire size for the 12v fuse block.

In description of the fuse block, it says the block has a 100A minimum.

Next, determine how far away from the power source you plan on mounting the fuse block.  We are going to mount our fuse block 10 feet away from the bus bar.

Next, we use our wire size chart to determine how big of wire we need.

100 amps over 10ft calls for a 1ga wire.

Now that we know how big of wire we are going to use, we need to determine how big of a fuse we need.

Oh, lookie there, Blue Sea tells us in the instructions how big of a fuse to use.

Now, double check that the 125A fuse requested by the fuse block in within the safe threshold for 1ga wire:

The 125 amp fuse requested by the fuse block is WELL within the maximum fuse size tolerance for our wire.

Next, we are going to determine how big of wire and fuse we need to wire a string of lights.  These 12v lights are the lights we are basing our example on.  We are going to install 2 packs of these 12v lights which will be a total of 8 lights.  The product page says these are 3 watts each.

8 x 3 = 24 total watts

24 watts / 12.6 system voltage = 1.9 amps for the whole string (which we will round up to the nearest whole number)

For the “Distance from fuse block to appliance” we are going to go with the furthest light, which, let’s say, is 15 feet from the fuse block.

2 amps at 15 feet is calling for 12ga wire.

Find the size of fuse by multiplying the amps required by the device (2) by 1.5.

2×1.25 = 2.5 then we will round up to the nearest fuse size (in multiples of 5 amps) which would call for a 5 amp fuse.

Cross Reference that fuse size to verify that it’s below the Maximum fuse size called out by this chart.  As you can see, 5 amps is well within the 52.5 maximum fuse size threshold.

And there you go! There are a lot of steps to this and trust me, you’ll get faster at it with practice. As always leave any questions you have in the comments below and subscribe for updates.

Now that you know how to size the fuses in your DIY Camper Van electrical system, it’s time to put everything you’ve learned to work.

Everything that you are learning here is put to use in our FREE Interactive Solar Wiring Diagrams.  If you haven’t yet, check them out as they are a complete solution for a camper van electrical system.  Check them out here: https://www.explorist.life/solarwiringdiagrams/

Remember, this is just one part of a full camper van electrical educational series.  To see all of the individual guides, click here: https://www.explorist.life/diy-campervan-solar

18 thoughts on “How-to Size Fuses in a DIY Camper Van Electrical System”

  1. I’m using three Renology 160 Watt solar panels and four 100 Ah LI batteries. What needs to change on the diagram for me to successfully install this system?

    1. You’ll only need to change the fuse between the solar panels, the charge controller, the wire between the charge controller and busbar, and the fuse between the charge controller and busbar. You can learn how to size all of that here:

      https://www.explorist.life/how-to-choose-a-solar-charge-controller-for-your-camper/

      https://www.explorist.life/what-wire-to-use-for-diy-camper-solar-system/

      https://www.explorist.life/what-size-fuses-to-use-for-a-diy-camper-electrical-setup/

  2. Hi Nate,
    It’s just amazing all the thing you have done in this website. A great great thank’s.
    I have a question, easy one. I want to start with a 330watts solar panel and 2 x 100 Ah lithium batteries. But if one day I want more watts with an other solar panel ,I’m better to choose a 60 amp controller ?
    Let me know if my thinking is good.
    And again thank’s for all !

    1. Thanks!

      I would definitely go ahead and size the charge controller for future expansion if that’s your plan.

  3. Hello,

    Thanks a lot for all the information you provide and for the way to calculate a lot of things.

    The main solar components for my DIY van build project will be: 600W panels (2 X 300W), One 12V 400ah Lifep04 lithium battery, the 2000W Victron inverter charger, the Victron MPPT 100/50.

    I am using the wiring diagram to adjust it for my needs based on your comprehensive e-book.

    I am almost all right to identify nearly all the components I need, but from the wiring diagram, there is the 4 units of ANL 250 Amp fuses and the 50 Amp resettable breaker close to the MMPT, for which I can not find the way to calculate if the values from the wiring diagram will be good for my own setup.

    Can you provide me more detail on the way to calculate the good values, or provide me the right numbers I should use?
    Thanks in advance for your answer

    Philippe

  4. I have 600 watts of panels on my Ford Transit , the MPPT 150/45 and the 12v 3000w 120 amp Victron. I am getting close to starting it up. I have 2 100amp Battle Born lithiums. I went with the 30 amp breaker from your diagram between the panels and the MPPT. Am I good with that?

  5. Loved the post about fuses. I blew one recently using an air compressor on the vans 12v supply and it was a nightmare to fix. You’re post really helped me understand my requirements better. Our installer hadn’t even marked the connections correctly!

    Your site is really inspirational. Three years into the journey already. Mine is only just starting out after quitting work last week to travel full time.

  6. hi! I have 4 100watt renology solar panels and 3 100amp life po4 lithium batteries for my van conversion and don’t want to hook up getting energy from the motor or anything. I’m a bit confused on what fuse to get or if there’s anything I’ll need to change to have my van build work. Also, would a Aims Power PICOGLF20W48V120VR Pure Sine Inverter Charger, 2000 Watt Low Frequency Inverter, 6000 Watt Surge work with my Victron MultiPlus Compact 12/2000/80-50 120V VE.Bus Inverter Charger? I couldn’t find a two in one.. or do I even really need the aims power? I would really appreciate the help thank you!

  7. Hey Nate, Very helpful site! I have one question, why is the resettable breaker in between the solar panel array and the charge controller rated at 15A? I’m planning to wire up 2 x 200W panels in series and for the future, I am counting on a max amperage of 10A coming from my panels. The wires will run for approximately 5-6meters. This means that the fuse size for that wire should be around 6ga with a recommended fuse of 100A, so why the 15A breaker? Thanks in advance.

    1. So, a downfall of that chart is that it doesn’t take into account any voltages over 12V. When you wire your solar panels in series, you’ll be pushing nearly 40 volts. Wire size can decrease as voltage goes up, so…

      I have a wire sizing calculator I use and I just plugged in your parameters and 9 amps at 38 volts (panels wired in series) allowing for a max of 3% voltage drop, 10 awg will be good until you get to 105 feet.

  8. Hi Nate,

    This is all great information as I’m starting my project. I was just curious, I didn’t see you mention how you size the bus bars for the system. Do you have that somewhere in here?

    I am using a Victron 12/3000/120, 3 Battleborn 100ah Lithium Batteries and the Victron 250/100 Solar Controller and Sterling B2B Charger.

  9. Hi Nate. Love all the info on here. Kinda lost right now. I need to wire my inverter to my batteries. From what I can tell on the installation sheet, is that I need 2/0 wire, and it calls for a 240 amp T-fuse no more than 7″ from the battery. Would I be able to use a 250 amp T-fuse, because I don’t see anywhere that has a 240 amp T-fuse. Thanks.

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