The Ultimate Guide to Safe Electrical Systems , Fuses & more

The Ultimate Guide to 12V Fuse Boxes for Campervans

Knowing how to properly protect your campervan’s electrical system is crucial. Correctly installed fuses safeguard your setup from short circuits, overloads, and potential fires. In this guide, we’ll cover the differences between fuses and circuit breakers for AC and DC systems, how to size your fuses, choose the right type, and install a fuse box or distribution panel in your campervan. By the end, you’ll be ready to confidently dive into your van’s electrical system!

What is a Fuse and Why Are They Important?

A fuse is an electrical safety device designed to protect circuits from overcurrent. Simply put, it’s a metal wire that melts when too much current flows through it, stopping the electricity. The point at which the fuse "blows" is called its breaking capacity.

Fuses are critical for preventing electrical fires and protecting appliances and wiring in your campervan.

What’s the Difference Between a Fuse and a Circuit Breaker?

Both fuses and circuit breakers perform the same essential function—breaking an electrical circuit when a fault occurs. When a fuse blows, its wire melts, and it must be replaced. A circuit breaker, on the other hand, is a switch that can be reset after it trips.

Fuses are cost-effective and easily replaced, whereas circuit breakers are more expensive and trickier to install. However, circuit breakers' reset function makes them an attractive option for campervan conversions.

AC vs. DC Fuses and Circuit Breakers

For a quick overview of AC and DC systems, check out our guide. In short, it’s vital to use AC fuses for AC systems and DC fuses for DC systems. AC fuses typically handle higher voltages and resist electrical arcing better than DC fuses when they blow.

Fuse Performance: Terms and Ratings

• Voltage Rating: The maximum voltage the fuse can handle. Common ratings include 32V, 60V, 125V, 300V, 500V, and more.

• Minimum Fusing Current: The current at which the fuse melts. This is usually 1.25 to 2 times higher than the fuse’s rated current.

• Rated Current: The current listed on the fuse, which it can handle under normal conditions.

• Blow Time: The time it takes for the fuse to blow after the current exceeds the rated limit. Fuses can be ultra-fast, fast, or slow.
  

Circuit Breaker Performance: Terms and Ratings

There are two main types of circuit breakers: thermal and magnetic. Thermal breakers trip when a certain temperature is exceeded, while magnetic breakers trip when the current exceeds a threshold. Magnetic breakers are generally preferred for campervans.

• Voltage Rating: The maximum voltage the breaker can handle.

• Rated Current: The current listed on the breaker’s body.

• Trip Current: The current at which the breaker actually trips, often around 130% of the rated current.

• Trip Time: The time it takes for the breaker to trip once the current exceeds the trip current.

How to Choose the Right Fuse

Common Types of Fuses

• AGC/MDL Fuses (0.25A–30A): Glass tube fuses ideal for small appliances.

• Blade Fuses (1A–80A): Widely used in vehicles, color-coded, and easy to replace.

• Terminal (MRBF) Fuses (30A–300A): Designed for leisure batteries.

• MIDI/MEGA/ANL/Class T Fuses (30A–400A): Handle high currents, often used for inverters and battery chargers.
  

With this guide, you’ll have the knowledge to protect your van’s electrical system effectively and safely.

How to Choose the Right Fuse for a DC Circuit

Step 1: Calculate the Proper Wire Size

Before choosing a fuse, make sure the wire you’re protecting is properly sized. Learn how to size wires in our guide or use our handy wire size calculator.

Step 2: Select a DC Fuse

The general rule for sizing fuses is: "Always choose a fuse size that protects the wire according to its rating." However, campervan builders often oversize their wires for added safety.

To calculate fuse size, determine the total current of the appliances the wire supports and add a 25% buffer.

Example:
Let’s say you have eight 12V puck lights, each consuming 3W. The current for each light is:
3W÷12V=0.25A3W ÷ 12V = 0.25A3W÷12V=0.25A

For eight lights:
0.25A×8=2A0.25A × 8 = 2A0.25A×8=2A

Adding a 25% buffer:
2A×1.25=2.5A2A × 1.25 = 2.5A2A×1.25=2.5A

Choose a 2.5A fuse for this system.

Step 3: Select a Suitable Fuse Holder

Fuse holders come in two types: inline and block.

• Inline Holders: Compact and hold a single low-current fuse.

• Block Holders: Mounted on a fixed surface and can hold one or multiple fuses.

How to Choose a Circuit Breaker

Circuit breakers act as manual switches, allowing you to shut off parts of your electrical system. This is useful for troubleshooting, during the build process, or if you want a setup where each component can be easily isolated.

Select a circuit breaker the same way you would choose a fuse—calculate the appliance’s amperage and add a 25% buffer.

Regulatory Guidelines for Fuse and Circuit Breaker Installation in Campervans (BS 7671 & NEC)

Properly fusing your campervan's electrical system is essential for safety and compliance. Both the BS 7671: IET Wiring Regulations (UK) and the NEC (National Electrical Code) in the USA provide detailed instructions on using fuses and circuit breakers to protect against overcurrent and electrical faults. Below, we summarize the general principles for safe installation, but for a deeper dive, check out our detailed article on regulatory guidelines.

General Guidelines for Fuses and Circuit Breakers in Campervans

Sizing Fuses and Circuit Breakers: Both BS 7671 (533.2.1) and NEC (240.4) emphasize that fuses and circuit breakers must be sized to protect cables and devices from overcurrent. Typically, fuses are rated at 125% of the circuit's normal load. For example, a 10A load would require a 12.5A fuse.

Types of Fuses: Blade fuses are commonly used in 12V DC systems for low-current 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 that the fuse type matches the system’s power consumption and cable capacity.

Battery Overcurrent Protection: Both standards require batteries to be protected by terminal fuses or ANL fuses as close to the battery as possible. For instance, a 200Ah battery would typically require a 200A ANL fuse to safeguard against short circuits.

Breakers for AC and DC Circuits: Circuit breakers can replace fuses 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 designed for DC loads to prevent arcing and ensure circuit protection.

Using Distribution Panels: Install a 12V fuse box to centralize all DC circuits, with each circuit protected by a fuse matching its load (e.g., 5A to 30A blade fuses). For AC systems, use a consumer unit to organize circuit breakers and RCDs for comprehensive circuit protection.

By following these guidelines, you can ensure your campervan’s electrical system is safe, compliant, and protected against overcurrent and electrical faults. Proper sizing and installation of fuses and circuit breakers are key to creating a reliable and efficient setup.

Read our comprehensive guide to campervan electrical regulations (UK, USA, EU) for more detailed information.

Campervan Fuse Box (12V Fuse Box)

Most van converters install a simple 12V fuse box in their campervans. This serves as a central hub for protecting smaller 12V DC appliances like lighting, roof vents, water pumps, diesel or LPG heaters, and possibly your fridge.

12V fuse boxes typically use ATC blade fuses. Purchasing a "variety pack" of blade fuses is a smart idea—it’s crucial to have replacements on hand.

For solar-powered campervans, the fuse box is usually connected directly to the solar charge controller, offering a neat way to monitor the DC system.

For vans without solar power, connect the fuse box directly to the main busbars that link to your leisure batteries.

Most setups also include a switch panel between the campervan's fuse box and the 12V appliances, allowing you to control each appliance individually.

Inline DC Circuit Breakers

Platforms like Amazon, eBay, and AliExpress are flooded with counterfeit inline breakers that are hard to distinguish from genuine ones. These knock-offs offer no real safety value and should be avoided. They might fail to trip at the correct current, trip too early or late, or overheat near their rated trip point. For reliability, stick to trusted brands like BAS, Eaton-Bussmann, and Victron Energy when purchasing fuses and circuit breakers.

Blade Fuse Sizes

When selecting blade fuses for your 12V fuse box, ensure they are correctly sized. Blade fuses come in various types designed for specific applications and amperages.

• Mini Blade Fuses: Rated for 2 to 30 amps.

• Standard Blade Fuses: The most common and versatile, rated for 2 to 40 amps.

• Maxi Blade Fuses: Larger fuses for heavy-duty applications, rated for 20 to 100 amps.

Blade fuses are color-coded for easy identification.

Distribution Panels

Distribution panels (also called breaker panels or electrical panels) are common in homes and offices. In campervans, they replace fuses for AC systems. A distribution panel is a plastic box that splits electrical power into sub-circuits and provides protective breakers for each circuit.

AC Consumer Unit

A consumer unit, or breaker box, is a type of distribution panel. In van conversions, it’s used to manage shore power connections for plugging into campsite or service station mains electricity.

Consumer units house an RCD (Residual Current Device) and multiple double-pole MCBs (Miniature Circuit Breakers). For more details, check out our article on shore power connections.

You may also need a consumer unit between your inverter and wall outlets. Check your inverter’s manufacturer guidelines for requirements.

Combined AC and DC Distribution Panels

For vans with both AC and DC systems, a combined distribution panel is a neat way to house all fuses and breakers. These panels combine a 12V campervan fuse box with an AC consumer unit in a single enclosure.

Note: Exercise caution when installing AC and DC systems in the same cabinet. Never allow wires from the two systems to touch.

Tip: Explorist Life has an excellent video tutorial on wiring a combined distribution panel—check it out here.

Summery

We’ve covered everything you need to know to safely protect your electrical system. If you’re still unsure, take a look at our Electrical Masterclass for a step-by-step course on campervan electronics. Finally, we encourage you to consult a professional electrician for your system. With your fusing sorted, you can now read about complementing your 12V fuse box with a switch panel.

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