Knowing how to fuse your campervan electrical system is imperative. Correct fusing protects your electrical system from short circuits, blowouts, and fires. In this guide, you will learn about the differences between fuses and circuit breakers for AC and DC systems, how to size your fuses, how to choose the right fuse type, and how to wire up a campervan fuse box or distribution panel. By the end, you will be ready to confidently dive into your campervan electrical system.
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Shane, the founder of The Van Conversion, is a campervan professional dedicated to helping people transform ordinary vans into homes on wheels. He has authored Roaming Home, and teaches The Van Conversion Course, guiding many people through their van builds. Shane also writes The Van Conversion Newsletter, where he shares practical tips and insights. After completing two van builds and living on the road full-time since 2020, he is passionate about sharing his expertise with others.
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Supplies List
 | |
 | For fusing leisure batteries |
 | ANL fuses For fusing high-current circuits |
 | For holding ANL fuses |
 | MEGA fuses For fusing medium-current circuits |
 | MEGA fuse holder For holding MEGA fuses |
 | Protect your campervan electrical system in case of fault |
 | Breakers that can double as a switch |
What is a Fuse and Why are They Important?
A fuse is an electrical safety device that provides overcurrent protection to an electrical circuit. At the most basic level, it is a metal wire that melts when too much current flows through, thus stopping the flow of electricity. The point at which a fuse blows is known as its breaking capacity.
Fuses are critical to electrical systems in order to prevent electrical fires and damage to appliances and wires.
What is the Difference Between a Fuse and a Circuit Breaker?
Fuses and circuit breakers both carry out the same function; breaking electrical circuits in the event of a fault. When a fuse blows, the wire melts and it needs to be thrown away and replaced. In contrast, a circuit breaker is a switch which can be reset after it has been flipped.
Fuses are very cheap and can quickly be replaced by simply pulling them out. Breakers are more expensive and more difficult to remove. However, the ability for a circuit breaker to act like a switch makes them very attractive for van conversions.
What is the Difference Between AC and DC Fuses and Breakers?
For a recap on AC and DC electrics, you can read this guide. In brief, it's very important that you use AC fuses in AC systems, and DC fuses in DC systems. AC fuses can usually handle higher voltages. They are more resistant to electrical arcing when the fuse blows compared to DC fuses.
Fuse Performance: Terminology and Ratings
Rated voltage: This is the maximum voltage the fuse is rated to handle. The typical ratings are 32, 60, 125, 300, 500, 600, and 750 volts.
Minimum fusing current: This is the current (amperage) at which the fuse reaches a temperature where it will melt. The minimum fusing current is significantly higher (1.25 to 2 times more) than the rated amperage of the fuse.
Rated amperage: This is the amperage printed on the body of the fuse. It is less than the minimum fusing current. In other words, fuses can carry 1.25 to 2 times their rated current before blowing.
Melting time: This is the amount of time it takes for a fuse to blow after the current has crossed the minimum fusing current threshold. There are ultra-fast, fast, and slow blow fuses. Fast blow fuses are generally used to protect sensitive electronics.
Circuit Breaker Performance: Terminology and Ratings
There are two categories of circuit breakers: thermal and magnetic. Thermal breakers trip once a certain temperature is exceeded. In contrast, magnetic breakers trip when the magnitude of the current is exceeded. Magnetic breakers are generally preferred for van conversions.
Rated voltage: This is the maximum voltage the breaker is rated to handle.
Rated amperage: This is the amperage printed on the body of the breaker.
Tripping amperage: This is the amperage at which the circuit breaker will actually trip. It is normally about 130% the rated amperage.
Trip time: This is the amount of time it takes for a breaker to trip after the current has crossed the tripping amperage threshold.
How to Choose the Correct Fuse for a DC Circuit
Step 1: Calculate the appropriate wire size
Before choosing a fuse, it is important that you first size the wire you are fusing correctly. Learn how to size wires correctly in this guide, or use our handy wire size calculator.
Step 2: Select a DC fuse
The rule of thumb in fuse sizing is: 'always select a fuse size to protect the wire according to its rating.' However, amateur campervan builders should always size wires larger than they think they need. Most of us are not looking for maximum cost/weight efficiency, we are looking for maximum safety.
To calculate the fuse size, we should calculate the total amp rating of the appliance the wire is feeding and add on a 25% buffer.
Example: Let's say we have eight 12V puck lights which are 3W each. The amperage of each light would be 3W ÷ 12V = 0.25A.
We have eight of these lights: 0.25A × 8 = 2A.
We want to give ourselves a 25% buffer, so we will choose a 2.5A fuse for this system.
Once we know the fuse size we can go ahead and choose an appropriate fuse. Let’s look at some of the most common fuses.
AGC and MDL fuses [0.25A - 30A]: AGC and MDL fuses are slow blow fuses. They are constructed of glass tubing and brass end caps. The glass tubing provides a visible indication when the fuse blows. They are cheap fuses used for small appliances.
Blade fuses [1A - 80A]: Blade fuses are the most common fuses found in vehicles. They are cheap, colour coded, and easy to replace. When the fuse blows, it is visible inside the plastic casing. Van converters will tend to use ATO (ATC) blade fuses in their 12V campervan fuse box. They are used with small to medium sized appliances. ATO fuses are designed to handle 1A to 30A and MAXI fuses are designed to handle 30A to 80A.
Terminal (MRBF) fuses [30A - 300A]: Terminal fuses are almost exclusively used for fusing leisure batteries. They are rated to handle a large current and attach conveniently straight to the leisure battery terminals.
MIDI, MEGA, ANL, and Class T Fuses [30A - 400A]: These fuses are all designed to take a large current. Most of them are inline fuses, meaning they are installed on the wire. In van conversions, we use ANL and MEGA fuses to fuse things like inverters and battery chargers.
MIDI fuses are designed to handle 30A to 200A, MEGA fuses are designed to handle 100A to 300A, ANL fuses are designed to handle 35A to 400A, and Class T fuses are designed to handle 110A to 400A.
Step 3: Select the appropriate fuse holder
After you have chosen the appropriate fuse, you will need a fuse holder for it. The choice of fuse holder really comes down to the purpose of the fuse and where you'll be mounting it.
There are two types of fuse holder: inline and block.
Inline fuse holders are compact and hold a single low-amperage fuse. Block fuse holders mount to a solid surface and may hold a single fuse or multiple fuses. The 12V campervan fuse box we'll discuss later is a block fuse holder, but they also come in smaller sizes.
How to Choose a Circuit Breaker
Circuit breakers act as manual switches, allowing you to turn off parts of your electrical system. This can be useful when troubleshooting or building your system, or if you want a system where each component is easy to isolate.
Choose a circuit breaker the same way you choose a fuse, by calculating the appliance's amperage and adding a 25% buffer.
Amazon, eBay, and Aliexpress seem to be flooded with fake inline breakers that are indistinguishable from genuine ones. These knock offs have no value as safety components and should be avoided. They might not trip at the current they should, tripping early or late, or they might run very hot near their trip current. When buying fuses and breakers, buy them from trusted brands like BlueSea, Eaton-Bussmann, and Victron.
Regulatory Guidelines for Fuse and Circuit Breaker Installations in Campervans (BS 7671 & NEC)
Correctly fusing your campervan's electrical system is essential for safety and compliance. Both the BS 7671: IET Wiring Regulations (UK) and the NEC (USA National Electrical Code) provide detailed guidelines for using fuses and circuit breakers in campervans to protect against overcurrent and electrical faults. We summarise the general principles of safe fusing below, but take a look at our detailed article on regulatory guidelines for a full breakdown.
General Fuse and Circuit Breaker Guidelines for Campervans (Cross-regulation)
Fuse and Circuit Breaker Sizing:
Both BS 7671 (533.2.1) and NEC (240.4) stress that fuses and circuit breakers should be rated to protect the wire and devices from overcurrent. Fuses are typically rated 125% of the circuit’s normal load. For example, a 10A load should have a 12.5A fuse.
Types of Fuses:
Blade fuses are commonly used in 12V DC systems for low-power applications, such as lights or fans. For high-current applications like inverters, use ANL, MIDI, or MEGA fuses, which are rated for currents between 30A and 400A. Ensure the fuse type matches the current draw of the system and the wire capacity.
Overcurrent Protection for Batteries:
Both standards require batteries to be protected by terminal fuses or ANL fuses as close to the battery as possible. For a 200Ah battery, an ANL fuse rated at 200A would provide adequate protection against short circuits.
Circuit Breakers for AC and DC Circuits:
Circuit breakers are an alternative to fuses and can be used to protect both AC and DC circuits. For AC shore power, install double-pole MCBs to isolate both live and neutral wires during a fault. For DC systems, use thermal or magnetic breakers rated for DC loads to prevent arcing and ensure circuit protection.
Use of Distribution Panels:
Install a 12V fuse box to centralize all DC circuits, with each circuit protected by a fuse matched to the current load (e.g., 5A to 30A blade fuses). For AC systems, install a consumer unit or distribution panel to organize circuit breakers and RCDs for comprehensive protection of all AC circuits.
By following these guidelines, you ensure that your campervan’s electrical system is safe, compliant, and protected against overcurrent and electrical faults. Correct fuse and circuit breaker sizing, along with proper installation, are key to a reliable and efficient campervan setup.
The Campervan Fuse Box (12V Fuse Box)
Most van converters will install a simple 12V fuse box in their campervan. This is a central point from which we fuse up our smaller 12V DC appliances. These appliances might include lighting, a roof vent, a water pump, our diesel or LPG heater, and possibly our fridge.
12V fuse boxes typically take ATC blade fuses. Buying an "assortment pack" of blade fuses is probably a good idea - it's important to have them on hand for when you need them.
If we are running solar power in our campervan, we will typically wire the fuse box directly to the solar charge controller, which allows us to get some pretty nifty monitoring of our DC system.
If you do not have solar power in your campervan, wire the fuse box directly to the main busbars which connect to your leisure batteries.
We will typically install a switch panel between the campervan fuse box and the 12v appliances. This allows us to individually switch the appliances on and off.
Blade Fuse Sizes
When choosing blade fuses for your 12V fuse box, you need to make sure they're of the right size. There are several types of blade fuses, each designed for specific applications and rated with different amperages. The most common blade fuse sizes include mini, standard, and maxi. Blade fuses are often color-coded for easy identification.
Mini Blade Fuses: They typically come in amp ratings ranging from 2 to 30 amps.
Standard Blade Fuses: The standard-sized blade fuses are the most widespread and versatile. They are available in amp ratings from 2 to 40 amps.
Maxi Blade Fuses: Maxi blade fuses are larger and designed for heavy-duty applications. They usually have amp ratings from 20 to 100 amps.
Distribution Panels
Distribution panels (also known as panelboards or electric panels) are found in just about every home or office building around the world. They are typically used instead of fuses for AC systems. A distribution panel is a plastic box that divides an electrical power feed into subsidiary circuits, while providing protective circuit breakers for each circuit.
The AC Consumer Unit
A consumer unit or breaker box is a type of distribution panel. In a van conversion, we use a small consumer unit if we are installing shore power for plugging into mains at campsites and service stations.
The consumer units contain an RCD (residual current device) and several double pole MCBs (miniature circuit breakers). We discuss consumer units in much more detail in our article on shore power hook-up.
We may also need to install a consumer unit between our inverter and our plug sockets. The manufacturer of your inverter will specify if there's a need for a separate consumer unit.
While we normally use 12V fuse boxes with our DC system, we can use a DC consumer unit instead. This has the benefit of using switchable circuit breakers rather than fuses. This is rarer, and most people instead opt for a 12V fuse box paired with a switch panel.
Combined AC and DC Distribution Panels
If you are running both an AC and DC system in your campervan, a sleek way to house your fuses and circuit breakers is by using a combined distribution panel. It combines a 12V campervan fuse box with an AC consumer unit, all in one neat container.
Note: You must be extra careful if you are installing the AC and DC systems in the same cabinet. Under no circumstances should the wiring touch.
Explorist Life put together a really excellent video on how to wire up a combined distribution panel which you can check out here:
Conclusion
We've covered everything you need to know to safely fuse your electrical system. If you're still unsure, take a look at our electrical masterclass for a step-by-step course on campervan electrics. Ultimately, we would encourage you to consult a professional electrician about your system. With your fusing planned out, you might like to read about accompanying your 12V fuse box with a switch panel.
Don't forget to subscribe to The Van Conversion Newsletter for everything you need to get started with your own van conversion (we'll send you a free wiring diagram when you join).
If you're looking for some guidance with your van conversion, you might be interested in our book Roaming Home, or in our online course The Van Conversion Mastery Course. You'll learn directly from our founder Shane how to convert a van into your dream home - no prior experience needed.
Until next time.